6:

SOME ASPECTS OF THE BITING FLY PROBLEM

IN CANADIAN SUB ARCTIC REGIONS

Brian Hocking, University of

Department of Entomology. September

Alberta

1948

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in 2018 with funding from
University of Alberta Libraries

https://archive.org/details/someaspectsofbitOOhock

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PREFACE

More accurately known as the bloodsucking rather than
the biting flies, the insects dealt with in this paper include
the mosquitoes, the blackflies or buffalo gnats, and the horse-
flies and deer flies. Collectively these insects cause a
great deal of discomfort to man over very large areas of Canada;
they cause sickness and death in his domestic animals and birds,
and sometimes even the death of human infants, and more rarely
of adults .

The work recorded in this paper was carried out mainly
during the springs and summers of 1947 and 1948, on behalf of
the Defence Research Board of the Canadian Government Department
of National Defence. The primary object was to provide information
which would enable some mitigation of the nuisance of biting flies
to personnel of the armed forces, and to others whose duties lie
in regions heavily infested by these insects.

Both in 1947 and in 1948 a Canadian team of personnel from
the Division of Entomology and from the Defence Research Board,
and aU.S, team from the U.S. Bureau of Entomology and Plant
Quarantine working on behalf of the Surgeon General, Department
of the U.S. Army, were in close cooperation. Generous assistance
was received from a great number of other persons and organisations
at various times. While the present author was primarily
responsible for all the work reported hereafter in detail, for
the sake of coherence and continuity brief reference has been
made to work of other members of the parties. I would like to
record my appreciation of the generosity of Mr. W.C. McDuffie
and Mr. H.F. Cross of the U.S. Bureau of Entomology and Plant
Quarantine in allowing me to refer to the as yet unpublished
results of their work on mosquito larvicides and on repellent
chemicals, and of Dr. C.R.Twinn of the Division of Entomology,
Ottawa in permitting the use of data on the species and succession
of species of mosquitoes and blackflies in 1947. Acknowledgements
are also due to Dr. Alan Stone and Dr. Harold Morrison of the
U.S. Bureau of Entomology and Plant Quarantine, to Mr. G.E.Sh ewe-11
of the Division of Entomology, Ottawa, Professor E. B. Mains of
the University of Michigan, Professor E. A.Steinhaus of the
University of California, and Professor T. Fetch of King's Lynn,
England, to Professor E.H.Stri ckland, Professor B.H.Moss,

Professor J.H. Whyte, Professor R.B. Miller, and Mr. E. Moore for
assistance in the identification of specimens in their respective
fields. Also to Professors L.A.Thorssen and G.WQGovier for
assistance on matters relating to the measurement of stream flow
and the flow of insecticidal fluids, and to Professor M. LI. Cantor
and Mrs P. A. Wight for the analysis of nectar samples; to the
administrative staff of the military camp at Churchill and
Mr. A. C. Jones of the Defence Research Board for countless services
which I had no right to expect. Finally, and perhaps most of
all, to each and every member of the Canadian and U.S. parties
at Churchill in 1947 and 1948 for their unfailing cooperation
at literally all times.

* With the exception of experiment 1 in 5.1.1, q.v.

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CONTESTS

ABSTRACT

1.

2.

3.

4.

5.

6 .

THE CHURCHILL EMVI RONMEMT .

1.1. Climatic Conditions. . .

1.2. Other Ecological Conditions. ........

THE SPECIES AND SUCCESSION OF SPECIES

OF BITING FLIES AT CHURCHILL .

2.1. The Mosquitoes (Culicidae:Diptera> •■....

2.2. The Blackflies (Simuliidae: Dipt era) .

2.3. The Horseflies and Deer Flies* .......

(T abani dae : Di pt er a)

2.4. Other Biting Insects. * . .

OBSERVATIONS ON THE BIOLOGY AND BEHAVIOUR

OF THE BITING FLIES . . . .

3.1. The Mosquitoes .

3.1.1. Immature Stages: .

3.1.2. Emergence and Mating: . . .

3.1.3. Adult Feeding and Activity: .

3.1.4. Flight Range: . . . . .

3.2. The Blackflies. .

Q *2 rpv o T* onjarn rSo.

THE # I NFLU ENCE OF BITING FLIES ON MAN

AND ON HIS ACTIVITIES . . . . .

4.1. Physiological Influences .

4.2. Psychologi cal Influences.. .........

4.3. Indirect Influences . . . . .

EXPERIMENTS ON THE CONTROL OF BITING FLIES

5.1. Chemical means for the Reduction of Numbers.

5.1.1. Experiments with the Hochberg-Lamer

aerosol generator against mosquito
larvae* .......... .

5.1.2. A test of the Besseler generator

against adult Mosquitoes: .

5.1.3. Immature Stages of Blackflies: . . .

5.2. Protection of the Person from Biting Fly

Attack. . . . .

5.2.1. Repellents: . . .

5.2.2. Clothing and Shelters: .......

5.2.3. Other Aspects of Protection and

Control: ...... .

SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS . .

6.1. Summary of Control Conclusions. ......

6.2. Recommendations for Further Work .

2

2

7

12

12

19

24

27

28
28
28
30
32
45

.51

55

60

60

64

68

.70

72

94

103

145

146
148

152

155

155

156

REFERENCES

SELECTED BIBLIOGRAPHY

APPEN DI CES

ILLUSTRATIONS

1. The frequency of Wind. from each Direction ...... 4

2. The mean Wind Speed from each Direction . 4

3. The total Mileage of Wind from each Direction .... 5

4. Wind Mileage during Mosquito. Activity . 5

5. Average biting Rale of Mosquitoes . . . .15

6. The SucceSvSion and relative Abundance of tabanid
species at Churchill. ............... .25

7. A. punctor preparing to feed on H ab en ari a hvPerb o r e a . .35

8. A. nearcti cus feeding on man (1) . 38

2. A. nearcti cus feeding on man (2) . 38

10. The tundra 24 hour collecting site . 40

11. The wooded 24 hour collecting site . .40

12. A general view of the 24 hour collecting area . . . .41

13. Mosquito Activity and weather - Tundra . . . 43

14. Mosquito Activity and weather - Forest . . 44

15. Mosquito Flight Range . 50

16. A mature egg of Simulium venustum . 53

17. Ovi position site of S. venustum . 53

18. Tabanids in flight around a stationary vehicle . . .58

19. A typical reaction to the Puncture of a Mosquito

in a susceptible individual . 65

20. A typical reaction to Blackfly Punctures . 65

21. The 'Removal Reaction' (1) . (white wrhale in foreground) 67

22. The 'Removal Reaction' (2) . . . . . . 67

23. Map showing the location of plots treated with DDT

aerosols . . . .73

24. Layout of aerosol larvicide plots . 76

25. Snowmobile with amphibious trailer carrying Aerosol

equipment . 77

26. A general View of the area of Experiment 1 . 77

27. Oil film on surface of Pool 50 yards from base line

in experiment 1 . 80

28. A general view of the Grassy area in Experiment 2 . .80

29. A general view of the Shrub covered area . 86

30. Station 11, a Typical dipping Station . 86

31. Mortality graphs from aerosol larvicide tests . . . . 90

32. A general view of the Terrain used in the Besseler

generator test. . . 97

33. The Besseler generator in an amphibious trailer , . . 97

34. Layout of plot used with Besseler generator .... .98

35. Map showing the location of Blackfly breeding

streams treated with insecticides . 109

36. Goose River, treated in experiment 8, 1947 .... 122

37. Herriot Creek, treated in 1948 122

38. Mortality per cent of Blackfly pupae . 136

39. Insecticide dispenser for Stream Treatment (1). . . 171

40. Insecticide dispenser for Stream Treatment (2). . . 171

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ABSTRACT

The species of blood-sucking flies of the families
Culicidae, Simuliidae, and Tabanidae occurring in the vicinity
of Churchill, Manitoba are listed. Some notes on the
succession of species, larval habitats, and life histories
of these species at Churchill are given, and some investigations
into adult feeding habits, behaviour, and a new approach to
the study of flight range are reported on. The influence of
these insects on other organisms, and especially on man and
his activities are considered in some detail. Experiments
are described on the toxicity of some of the newer insecticides
to all stages of mosquitoes in the field, and to the immature
stages of blackflies under laboratory and field conditions.

The possibility of utilising these materials for practical
control measures is considered. Methods of personal protection
from all three groups of insects are discussed and suggestions
are made for improvements in these. 40 line drawings and
photographs illustrate the text, and data are presented in
8 tables and 7 graphs. The paper concludes with 85 references,
a selected bibliography, and appendices listing the birds
of the area and describing equipment for the routine
application of insecticides to streams.

T ::i A .. V? bo. ix

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1. THE CHURCHILL ENVIRONMENT

1.1. Climatic Conditions.

Churchill is situated at approximately latitude 59°

N. and longitude 94° W. , on the western shore of Hudson Bay,
at the mouth of the Churchill River. It lies inside the
Sub-arctic area, about 170 miles from its northern boundary.

In winter Churchill is one of the coldest spots in

northern Canada. The snowfall is light, and high winds off

snow cover

Hudson Bay prevent this forming much persisteny, but cause
drifting which may bury buildings. Very high wind chill figures
are recorded, winds of 40 m.p.h. with temperatures down to
-7Q°F being not uncommon. The summer weather however, may be
unpleasantly hot and humid.

During the periods of entomological work at Churchill,
daily weather summaries consisting of six-hourly readings of
relative humidity, temperature, wind direction and speed,
barometric pressure, and extent of cloudiness, and daily records
of precipitation, were kindly provided by the Department of
Transport meteorological officer. Supplementary records of
special and local conditions in connection with specific items
of investigation are given with the items to which they refer.

An analysis of the general weather records shows that
the average temperature for the 87 day period from May 16 to
August 10, 1947 was 47°F, the averages for May (part), June,
July, and August (part) being 24.5, 44.8, 58.3, and 54.5°F

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respectively. The range of temperature was 73 Fahrenheit
degrees, from a low of 9°F on May 17 to a high of 84°F on June
20 and July 12. The relative humidity was high throughout the
period, but particularly so before the thaw. The average figure
for the whole period is 85.5 per cent; that for May (part) is
91.5 per cent and that for the remaining period separately 84
per cent. Relative humidity figures had a range of 57 per cent
from a low of 43 on June 18 to 100 per cent on several days;
daily averages ranged from 63 on June 19 to 100 per cent. No
definite trends appear in the figures for barometric pressure.

Wind speed showed a slight general decrease from May
to June and July, followed by an increase early in August. The
average wind speed for the whole period was 12.6 m.p.h. ;
averages for each of the months separately were 14.3, 11.8,

11.9, and 14.7 m.p.h. respectively. The range of wind speed
was from calm on May 18, July 13 and 16, and on August 3, to
45 m.p.h. on May 24 and 36 m.p.h. on August 6. The question of
wind direction and the combination of this with wind speed has
been treated in greater detail in view of the possible impact
of these factors on the shift of insect populations, especially
those of mosquitoes. Figure 1 shows the frequency with which
the wind blew from each direction; apart from the scarcity of
E and SE winds, there is no well marked trend although NE, and
W to NW winds were somewhat more common. Figure 2 shows the
mean wind speed for each direction; the scarcity of E and SE
winds is to some extent compensated by their greater mean speeds.
Figure 3 represents the product of mean speed and frequency,

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FREQUENCY OF WIND D I R ECT I ON

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MEAN WIND SPEED FR0M EACH

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TOTAL MILEAGE OF WIND ^ *** DIRECTION

WIND MILEAGE — MOSQUITO ACTIVITY

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and gives a picture of the general trend in the movement of
air at Churchill throughout the whole period; the vector sum,
representing a mean speed of 2.0 m.p.h. on a bearing of 311°
(approximately NW ) , is indicated by the solid column. Figure
4 gives the same data as figure 3, but covers the period of
significant adult mosquito activity only; from dune 20 to July
20. There was a much clearer preponderance of HE wind during
this period, but the vector sum represents a mean speed of only
0.15 m.p.h. on a bearing of 39° (approximately NE ).

The total precipitation during the period was 5.18
inches water equivalent, of which 0.08 inches was in the form
of snow. This precipitation was distributed between the four
months as follows: 0.18, 0.91, 0.95, and 2.90 inches, the
maximum rainfall on any one day being 1.63 inches on August 5.
There was measurable precipitation on 36 of the 87 days; on seven
of the 16 days in May, ten days in June, 12 days in July, and
seven of the ten days in August.

Observations of cloud conditions during the hours of
daylight may be summarised as follows: 53 per cent overcast,

40 per cent partly cloudy, 7 per cent clear.

The ice went out of the Churchill River on June 20
1947; the expected date for this occurrence being that of the
spring tides closest to June 15 (5), the season at this stage
was nearly a week later than normal. A comparison of average
temperatures for June and July of this year with similar
averages obtained over a number of years (6) supports the
impression obtained from residents that by the end of July the

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season was normally advanced.

Weather data for 1948 are still accumulating so that
a complete analysis is not yet possible. The season was very
much earlier to start with, but cold weather early in June
retarded development until by early ^Fuly conditions were
comparable with those obtaining at this time in 1947 although
very much drier.

1.2. Other Ecological Conditions.

Within a radius of a few miles of Churchill is to be
found a great variety of terrain, including spruce-larch forest,
muskeg, tundra, tundra-meadow, birch-willow scrub, low limestone-
gravel and granite ridges, tidal flats, and sand dunes. It is
a zone of transition from forest to tundra and supports a varied
insect fauna including species of biting flies typical of the
forest and of the plain and of the sub-arctic and the arctic.

The northern fringe of the sub-arctic forest extends
to within a short distance of Churchill. In this region it is
rather open and swampy and consists chiefly of stunted trees
rarely exceeding 50 feet. The forest floor is for the most
part soft and spongy underfoot, very tiring to walk on and often
treacherous to the unwary.

The tundra and tundra-meadow in the area extends from
the scattered tree growth along the uneven margins of the forest

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to the shore of Hudson Bay. The predominant vegetation consists
of lichens, coarse grasses and mosses, hut other flowering
plants also abound, their successive blooming adding a touch
of colour and beauty to the otherwise rather bleak landscape.
Where soil conditions are favourable, dwarf spruce grow singly
or in small clumps. In exposed situations overlooking Hudson
Bay the branches of these trees grow out only on the south side
of the trunk; or the whole tree may have a prostrate form,
spreading out in a mat a few inches above the surface of the
rock as if to take full advantage of the meagre heat reflected
from this. In protected situations such as along the borders
of streams, dwarf birch and willow grow, in places forming
dense thickets.

Large numbers of aquatic and wading birds nest and
raise their young in the marshes and swamps of the Churchill
region. Common among them are ducks, geese, gulls, terns,
sandpipers, plovers, curlews, and ptarmigan. Among them, too,
is that familiar habitue of suburban gardens, the American robin.
Mammals are much less in evidence. A few caribou were seen
near the Churchill River and along the shore; also two porcupine
in the forest and a number of larch trees stripped of bark by
their feeding. Burrows and trails of small rodents are numerous,
but their numbers were at a low ebb in 1947 (14,52), the animals
themselves were rarely seen and, in spite of several attempts to
trap them, only three lemming were captured. From these, 2 males
and 6 females of the flea Megabothris groenlandicus Wahlgren
were taken (det. G. P. Holland) . In 1948 mice and lemming were
more numerous, and rabbits and the fresh tracks of wolves were

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seen. Schools of white whales enter the mouth of the Churchill
River after the ice goes out, and numbers of these are killed
for their meat and oil by local Indians and trappers. Of fish,
pike, grayling, and suckers abound in the larger streams and
serve as a major part of the diet of sled dogs during their
enforced summer idleness, as well as being preserved for
winter use. Sticklebacks were much more numerous in 1948
than in 1947. No reptiles were seen, but frogs were common
in the marshes, and specimens collected were identified by
C.L. Patch, of the National Museum, Ottawa, as the northern
wood frog, Rana sylvatica cantabrigensis.

Drainage is generally poor in the Churchill region
because much of the terrain is low-lying and the ground is
permanently frozen a short distance beneath the surface. As a
result, innumerable shallow pools form on the tundra and in the
forest during the spring thaw and serve as breeding places for
the countless hordes of mosquitoes that appear on the wing in
late June and July. What drainage there is occurs largely
through numerous streams that flow into the Churchill River
or into Hudson Bay. From these streams and from the rapids of
the river, vast numbers of blackflies emerge and, with the
mosquitoes, and the bloodsucking tabanids that develop in the
forest, plague man and beast throughout the short summer.

The biological violence of this short summer is a most
striking feature, to one accustomed to the living continuum of
the tropics, and can perhaps be conveyed best by a rapid survey
of the sequence of events as observed in 1947.

The conspicuous insect life at the end of May

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consisted of springtails on the melting snow and ice, sometimes
in such abundance on trails that they are reported to impede
the passage of sleds, and various small flies, mainly
dolichopodids and mycetophilids on the surface and at the
margins of pools.

By June 5 the smaller streams were beginning to flow,
although ice remained at the bottom. Stonefly nymphs, previously
solidly frozen, were active inside pockets of water formed
inside blocks of ice presumably by radiation absorbed by their
own dark bodies. Pools at this time contained many chironomid
and dytiscid larvae and gerrid nymphs, and birds were courting
on the marshes. Flowers of the mountain saxifrage, Baxifraga
oppositifolia , the first plant to be found in bloom were
collected on June 15, and by this time dung flies and bumble
bees were flying, and most birds were sitting on eggs.

By June 22, larch, willows and birch were coming into
leaf, and many ericaceous plants, especially species of Ledum,
Rhododendron, and Andromeda were flowering. Chironomid adults
were locally numerous, and well grown caddis larvae abundant in

pools and streams.

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The first week of July brought out the first families
of ducklings and ptarmigan, many more plants were newly in
flower* the sweet coltsfoot, Petasites sp. conspicuous amongst
them, and arctic heather, Dryas integrifolia , several times as
abundant as any other flower. Among insects adult dragonflies
and caddis flies were on the w ing.

The replacement of arctic heather by cotton grass,
Arlophorum sp., as the most abundant flower marked the middle

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11

of July; by this time the eggs of plovers and terns had
hatched, and half grown tadpoles were to be found in many of
the pools. Most groups of insects were represented by the
adult stage, those recently emerged including several species
of mayflies, weevils, and some syrphid and trypetid flies.

By the third week of July the peak of adult insect
activity was over, and the eggs of a great many species were
to be found in, and at the verges of, the now much diminished
pools and streams. The ox-eye daisy, Ch ry s an th emum arcticus,
and the conspicuous fireweeds, Spilobium spp. , were coming into
flower, the latter becoming extremely abundant.

An excellent account of the invertebrate ecology
of Churchill is given by McClure (38).

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12

2. THE SPECIES AMD SUCCESSIOM OF SPECIES
OF BITING FLIES AT CHURCHILL

2.1. The Mosquitoes (Culicidae: Diptera) .

Eight species of Aedes and two species of Culiseta
have been identified among the specimens collected or reared
in the Churchill area during 1947. No other genus of the
sub-family Culicinae was represented, but the predaceous
larvae of three genera of non-biting mosquitoes of the sub¬
family Chaoborinae, namely, Eucorethra. Mo chlonvx and Chaoboras.
were fairly common in the Culicine breeding pools. Unfortunately,
none were reared to the adult stage, but a male and a female
collected from a mating swarm at 4 p.m. on July 24 belonged to
the species Chaoborus nyblaei Zett.

The two species of ‘Culiseta represented are C. alas-
kaensi s Ludl., and C. impatiens Wlk. They are not abundant in
the area, only small numbers of overwintered females being
seen or captured during the month of June. No males or
aquatic stages of the species were found.

The species of Aedes definitely determined include
A. ni gripes Zett., A. punctor &by., A. nearticus Cyan., and
A. communi s Deg., occurring probably in that order of abundance;

A. campestris D.&K., and A. excrucians Wlk., less abundant, but
numerous and widespread; A. flavescens Mtlll . , and A. cinereus
Mgn., relatively few and localised in occurrence.

In 1948 several further species of Chaoborinae were
taken. Males and females of Mo chlonyx culi cl f ormi s DeG . were

t 3

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13

reared from pupae collected in the forest on July 17. Other
material has yet to be identified and may contain new species.
The larvae of Culi seta alaskaensis were collected and reared
to maturity in a field insect ary.

In the genus Aedes two species were recorded for the
first time in 1948. These were Aedes fitchii Felt & Young,
and A. spencerii Theo., neither of them common, but the latter
taken in most interesting circumstances. Only three specimens
were taken, all of them inside army vehicles at the beginning
of June, well before any other species of the genus had emerged
at Churchill either in 1947 or 1948. The weather at this time
was unusually warm, and winds had been continuously SSE at
speeds up to 22 m.p.h.; immature stages of A. spencerii have
never been taken at Churchill. It is most probable that these
specimens came in from further south, either wind borne, or on
aircraft or trains. The fact that the vehicles in which they
were taken were all within easy access of both the airport
and the railway station, suggests the latter explanation.

A. specerii is known to be a migratory species, and data on
the northern limits of its breeding would be very interesting.

Immature stages of A. cinereus were taken for the
first time in 1948, collected in the forest 12 miles south
of Churchill. Matheson identified A. nigromaculis Ludl. among
the mosquitoes collected here by McClure in 1936-7, but no
specimens of this species have been obtained.

All the species of Aedes found in the Churchill area
overwinter in the egg stage. In 1947 larvae began to hatch out
in small numbers in snow pools in sheltered places on the

v/; • - aio rs - jl ,1<~c s.oq^-

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14

tundra at the beginning of June, when snow and ice were still
prevalent in the area. By the middle of June, when the snow
was largely gone from the open country, the larval population
of several abundant species was nearing its peak in pools in
the open and among the sparse tree growth along the margins
of the forest. These species were A. ni gripes, A. punctor.
and A. nearcticus. Early stage larvae of A. excrucians had
also begun to appear. In the forest the first larvae of
A. communis were found hatching in favoured snow pools on June
9, when nearly two-thirds of the forest floor was still covered
with fast -melting snow.

Pupation of A. ni gripes began on June 16, and A.
punctor on June 17, the first adults emerging on June 20, and
June 21, respectively. Emergence of A. nearcticus started on
June 22, and that of A. communis in the forest on June 24.
Periodical collections indicate that these four dark-legged
species are the dominant ones in the Churchill region.

Towards the end of June emergence was general. During
the early part of July pupae were still common, but larvae
were becoming increasingly hard to find. By July 3, tremendous
numbers of mosquitoes were on the wing, and they continued to
increase until a peak of abundance was reached during the second
week of July (Fig. 5) . The pest species were augmented by adults
of A. campestris on July 5, A. excrucians on July 9, A. cinereus
on July 13, and A. flavescens on July 20. By the third week of
July, however, a definite falling off in abundance and aggress¬
iveness of the mosquito population was apparent, and by early
August, their numbers had reached relatively small proportions.

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AVERAGE BITING RATE OF MOSQUITOES

15

Figure

5.

.

16

The adult females of the four common species A.
ni gripes. A, nearcticus, A. punctor, and A, communist are
difficult to separate without associated males or last larval
exuviae, which makes specific biological observations difficult,
especially late in the season when much of the vestiture of
scales has been lost. The first two species are rather hairier
and are characteristic of the tundra; the last two smoother
and typical forest species. A. punctor, however, is more
mobile, and hence more often found in the open than is A.
communis, which at least when newly emerged tends to remain
very close to its larval habitat (62).

Typical specimens of A. ni gripes are much larger than
those of A. nearcticus and have a relatively longer proboscis,
the ratio of proboscis length to wing length being about 0.84
in the former and only 0.73 in the latter. The occasional
specimens of A. nearcticus which have small sub- lateral patches
of white scales on the mesonotum can be identified at once in
the field. The ratio of proboscis length to wing length in
A. punctor is 0.7 and in A. communis 0.64; typically, the former
can be recognised by the lateral expansions of the basal bands
of white scales on the abdominal terga, and by the tendency of
the black scales on the venter to form a median stripe instead
of transverse bands as in typical A. communis specimens. A.
communis sometimes develops in incredible numbers in quite
small woodland pools. Adults emerging from these pools are
much smaller than normal, presumably as a result of severe
overcrowding in the immature stage. It is interesting to
note that Mellanby (40) reports A. punctor as overwintering

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17

in the larval stage at latitude 69°N in Finnish Lapland.

A. cinereus is a small, dark mosquito of the forest,
the smallest in the Churchill fauna, and the only distinctive
black-legged species. It is late emerging, non-mi gratory,
and has a rather short proboscis.

A. campestris, the commonest of the species with the
tarsal segments ringed with white scales, is a most attractively
marked mosquito with its mixed black and white scales on the
wings, bottle green eyes, and well marked pattern of almost
silver and gold scales on the roesonotum. Late in the season
in 1947 this species was more troublesome than any other in
the military camp itself.

A. excrucians is next in abundance to A. camoestris.

It is a large dark distinctive mosquito, late emerging, and
according to Hearle (26) does not travel far from its breeding
grounds .

A. flavescens, a large yellow species, with white
banded tarsi, is a late appearing mosquito, individually
conspicuous, but of comparatively minor importance. Its life
history is fully dealt with by Hearle (27). In 1948 this
species put in a rather unexpected early appearance before the
end of June, after which there was an interval of nearly two
weeks during which no specimens were taken, before it reappeared
about the middle of July. This would suggest that under
certain conditions of rainfall the larvae may hatch out in
two broods.

Culiseta alaskaensis and C. impatiens are large
mosquitoes with white banded tarsi and black spots on the

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18

wings; alaskaensis having the more distinct wing spots, and
being the largest mosquito in the Churchill fauna. These
species both overwinter as adults -and are consequently the
first mosquitoes to appear in the spring, flying and biting
some two weeks before the earliest species of Aedes emerge.
Dr. Douglas Leechman of the National Museum, Ottawa, quotes
an entry in Peter Fidler's Journal for April 4, 1792, which

may be taken to refer to a species of Culiseta. This entry,

which reads as follows, was made near Fort Fitzgerald,
northwest of Lake Athabaska, just south of the northern
boundary of Alberta:

"Put up about •§- mile above the head of the rapids amongst

a deal of old Large Poplars we made a good fire & soon

after we were all very much surprised to see numbers of
muskettoes flying about altho the Snow was more than 10
inches deep on the ground every where on examination we
found that betwixt the Bark of the Poplars and the tree,
of the old Dry wood there was a large open space which
was full of muskettoes that have been in that situation
all vdnter in some places they was in large cakes of 2
Inches thick the heat of the fire had invigorated them
so as to be able to fly about in the manner before
mentioned”

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19

2.2. The Blackflies (Simuliidae: Diptera) .

Previous to 1947, blackflies had been collected at
Churchill in 1934, by A.M.Heydweiller, and in 1936 by H.E. McClure.
These collections were examined and identified by Twinn.

Heydweiller* s collection, all females except where
otherwise indicated, included six species which are listed as
follows, together with a statement of the numbers of specimens
and the period during which they were collected:

Simulium venustum Say, 121, July 11 - Aug. 30

S . vi ttatum Zett. , 34 (plus 4 males) July 8 - Aug. 15

S. ottawaense Twinn, 26, July 10 - Aug. 15

S . arcti cum Mall. 4, July 30

S. peris sum D.&S., 4, July 30 and Aug. 11

Eu simulium baffinense palens Twinn, 2, July 30.

McClure's collection was made up of many hundreds of
female specimens, mostly S. venustum and S . vi ttatum , but also
including four specimens each of S. arcti cum (July 11 - 23) and
B. subexcisum Edw. (July 11) .

Thus these two collections were comprised of seven
species. Among the specimens collected or reared during 1947,
eight species are represented, five of them being additional to
those collected by Heydweiller and McClure. The eight species
taken in 1947 are as follows:

Simulium venustum Say
Simulium vi ttatum Zett.

Simulium sp.

Eusimulium aureum Fri es

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Busimulium latipes Mgn
Busimulium species A,

Busimulium species B.

Busimulium species C.

Daring 1948, at the time of writing all species taken
previously had been collected as adults or reared from collected
pupae except 5. arcticum, and E. baffinense palens. In addition
several specimens resembling S, boreale Mall., specimens of
what appears to be another new species, close to S. venus turn,
and the first male specimens of E. aureum were taken, making
a total of 14 species collected in this region.

The fact that no pupae or male specimens of S. arcticum
have been taken suggests that this species, like Aedes spencerii,
is unable to overwinter at Churchill, but migrates in from
breeding areas to the south and west. This species is noted
for appearing sporadically in very large numbers at almost
incredible distances from its breeding grounds (46).

Si mu li urn venus turn is the most abundant of the black-
flies in the Churchill area and the most important pest of man.
The immature stages were found in all bodies of running water
examined wherever blackfiies were developing, including drainage
ditches, rills, larger streams, and rivers.

The first pupae were discovered in 1947 on July 3, in
a small stream in the camp area and adults commenced emerging
on July 5. Observations on several other streams indicated
that emergence was general in the area on this and subsequent
days. Females were first captured attacking humans on July 8,
by which date mosquitoes were reaching their peak. By mid July,

.

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21

the numbers of blackflies of this species were tremendous,
especially in wooded areas, and the streams contained heavy
infestations of eggs, larvae, and pupae, a condition that
persisted until early August, when observations ceased.

Further south, S. venus turn passes the winter in the
larval stage (60) but in the Churchill region it is believed
to overwinter in the egg stage, except possibly in the Churchill
River, which continues to flow all winter beneath the ice.

The smaller streams were frozen solid in the winter of 1946-7
and thawed out during the first week of June. At this time
small numbers of dead pupae and cocoons of S. venus turn from
the previous season were found attached to stones and to
vegetation in several of the streams, but no living pupae or
larvae were seen, and young larvae did not begin to appear
until after the middle of June, two to three weeks before
the first adults of this species were on the wing.

There appear to be at least two generations of
S. venus turn at Churchill and probably three or a partial third,
the generations overlapping, so that after the first adults
emerge all stages may be found together throughout the short
summer season. Apparently development continues until the
streams freeze up. According to an official of the Churchill
grain elevator, adult blackflies are present until the snow
flies.

Female specimens of S . vi ttatum were collected
east of the Churchill River, in the open, and in the woods
south of Churchill on June 21, 1947. These were the first
blackflies on the wing, and presumably developed from larvae

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22

that had overwintered in the rapids beneath the ice in the
Churchill River. The ice went out on June 20. Pupal skins
of this species were found on submerged rocks in the rapids
close to the shore line, at Mosquito Point, on July 9. The
pupae were not found in any of the numerous smaller streams
examined.

Edwards identified material reported by Longs taff (72)
as attracted to, and apparently biting man in enormous numbers
at latitude 64° 40* N on the west coast of Greenland, as this
species. There was no evidence of this species attacking man
at Churchill.

The material referred to as Si mu li urn sp. consisted of
two pupal cases in cocoons collected on a stone taken from the
Churchill River rapids at Mosquito Point on July 9. The cocoons
are boot-shaped, and the respiratory tufts of the pupae are
short and comprised of 16 filaments. The material may represent
an undescribed form.

Eusimulium lati pes was found in 1947 in a shallow,
stony, rather swift little stream that has its source in a
pool in the camp area and flows through open woods and marshy
meadows towards the Churchill River. Numerous well-grown
larvae and small numbers of pupae were found on* stones and
grasses in the stream on July 3, and were the first blackfly
pupae seen in the area. In 1948 specimens were obtained from
a variety of smaller streams. This species, which is widespread
in Europe was first recorded in North America near Hull, Que.,
by Twinn (60). It apparently has only one generation a year.

Six females of Eusimulium aureum were collected on

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23

July 24 and 25, and August 2, 1947, but no pupae were found.

In 1948 specimens were taken throughout the later part of the
season and in various localities. This attractive species is
widely distributed in North America.

Both sexes of Eusimulium species A were obtained
from pupae taken from three streams, two draining into Hudson
Bay and one into the Churchill River. Emergence of adults was
actively proceeding from one of these streams on July 6, and
may have commenced a day or two earlier, as on this date empty
pupal skins greatly outnumbered pupae. Newly emerged specimens
were crawling up the vegetation in large numbers and many of
the flies were also on the wing. Emergence of this species
from the other two streams was still in progress about a week
later, and females were taken on the wing on July 25. This
is apparently an undescribed species; the pupa has short, bushy
respiratory tufts, each consisting of 25 - 30 filaments,
arranged mostly in pairs on short stalks arising from a common
base. The cocoon is of indefinite shape.

Pupae and pupal cases of both sexes of Eusimulium
species B were taken from Goose River on July 8 and from stones
in the Churchill River rapids at Mosquito point, on July 9.
one pupa was found in collections from Eastern Creek on July 12.

Eusimulium species C is represented by one female
which emerged by July 12 from a pupa collected on July 6. The
respiratory tufts of this pupa each consist of numerous filaments
(30 - 40) branching out on short stalks from the dorsal surface
of a stout elongate main trunk. Further material of these
species was obtained in 1948.

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24

2.3. The Horseflies and Deer flies (Tabanidae: Diptera).

Only a relatively casual survey of this group of
insects was possible, the study taking second place to that on
mosquitoes and blackflies and to control experiments on these
two groups. The material obtained in 1947 consists of specimens
collected during the course of that work, and is comprised
entirely of adult females, no males or immature stages being
taken.

These specimens represent five or six species of the
genus Hybomi tra and four species of Chrysops. These species,
arranged within the genera in order of abundance are: Hybomi tra
affinis Kby., H. septentrionalis Loew, H. metabola McD. ,

H. zonalis Kby., H. hearlei Philip, and H. gracilipalpis Hine;
and Chrysops carbonaria Wlk., C. fur cat a Wlk., C. ni gripes Zett.,
and C . f ri gi da O.S.

The succession and relative abundance of these species
as indicated by the material available are shown in figure 6.

The first specimens taken were H. metabola, collected on July 5.
Three independent reports were received of men being bitten
prior to this (July 3) by flies which, from their descriptions,
could have been tabanids. The first specimens of H. affinis
were taken on July 6. This rapidly became the dominant species,
and remained so until the middle of August (when observations
were terminated) although in close competition with H. septen¬
trionalis from the third week of July onwards.

The earliest species of Chrysops to appear was

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25

THE SUCCESSION AND RELATIVE ABUNDANCE
OF TABANID SPECIES at CHURCHILL

SPECIES

JULY

AUGUST

HYBOMITRA

5

10

15

20

25

30-

5

10

METABOLA

AFFINIS

ZONALIS

SEPTENTRIONALIS

HEARLEI

CHRYSOPS

CARBONARIA

FR1GIDA

NIGR1PES

Figure 6.

26

G. carbonari a which was first taken on July 12. This was
the most abundant species of the genus until towards the end
of July, when it gradually gave place to a predominance of
C. fur cat a., which, with C. frigida and C. ni gripes, made its
first appearance a few days after G. carbonari a.

Hybomi tra zonalis with its striking yellow and black
abdomen was remarkable in that it put in an early appearance
on July 10, but was not taken again thereafter. All the specimens
of this species were collected in the camp area.

In 1948, all the species taken in 1947 were again
recorded, and in addition the tabanine species H. sexfasciata
Hine, and a species close to H. hinei Johnson; and the
pangonine species C . mi ti s O.S. Only two or three specimens
of the first two species were taken, but C. mitis was found
to be quite abundant late in the season in the forest 25 miles
south of Churchill. Many males were collected, including
those of H.gracili palpi s, taken in copula, and one specimen
believed to be H . s ept entri onali s ; the male of this species
has not yet been adequately described. A number of larvae
were also collected and are being reared. II. zonalis was
much more abundant in 1948, and several specimens were taken
as late as July 24, in the forest 25 miles south of Churchill.

Dr. H.H.Schwardt identified H. illota O.S. and H.
rhombic a O.S. among the material collected at Churchill by
McClure in 1936 and 1937. No specimens of either of these
species have been taken in this work.

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27

2.4. Other Biting Insects.

Apart from the three families already dealt with,
the only group of blood-sucking flies of any potential
significance at Churchill is the family Heliidae (Ceratopogonidae ) .
These insects are commonly known as the biting midges, or
no-see-ums, and present a somewhat different problem to the
previous groups, since their extremely small size permits
them to penetrate the ordinary protective nets and screens.

In 1947 no-see-ums were very scarce and only three
or four specimens were secured. In 1948 they were much more
numerous, and in a really favourable year, they might well be
quite troublesome. Several species of the genus Culicoides
were taken, but have not yet been identified; the taxonomy
of the group is difficult, and has received very little attention.

No species of the family Ehagionidae, the snipe flies,
has been recorded biting man at Churchill. One member of the
1948 party however received a significant bite from a spider
while in a forested area.

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28

3. OBSERVATIONS ON THE BIOLOGY AND BEHAVIOUR
OF THE BITING FLIES

This is a subject on which, at first sight, very
little progress seems to have been made; the difficulty however,
is a very natural one. As soon as the observer enters the
habitat of biting flies which use man as a host, the whole
attention of all of these flies is directed towards obtaining
the much sought after meal of human blood. The activities
on which observations are required cease abruptly, and the
would be observer becomes himself the object of observation.

No progress can be made with eliminating this difficulty
until more is known of the factors which attract these insects
to their hosts. As a result, most of the data obtained will
have to be based on circumstantial evidence, except for that
relating to blood meals from man.

3.1. The Mosquitoes.

3.1.1. Immature Stages:

The eggs of most species of Aedes will withstand
dessi cation and extreme cold, and as a general rule will not
hatch until they are flooded with water after having been
subjected to these conditions. Roubaud (78) and Gjullin et al
(67) have demonstrated the importance of chemical stimuli in
the hatching of the eggs of species of Aedes. More recently

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29

Abdel-Malek (1) has shown that eggs of A, trivittatus require
the presence of certain plant hormones in critical concen¬
tration for optimum percentage hatch. Eggs of Churchill
species of Aedes have been observed to hatch in the laboratory
when flooded with water from tundra pools, but no work with
specific plant hormones has yet been done on these.

Only few isolated observations on the behaviour of
larvae and pupae have been made, the period of larval abundance
being largely occupied with work on chemical control measures.
In addition to the normal wriggling method of locomotion
characteristic of mosquito larvae, the larvae of A. excrucians
have been observed in water flowing very slowly through a
drainage ditch, to maintain their positions in this ditch
with no apparent locomotory movements. Observations on the
intervals between submergence and surfacing for this species
have been made as follows: at the surface, 2, 2, 26, 3, 6,

2, and 4 seconds; submerged, 10, 123, 343, 8, 24, and 32
seconds. In general a long period of submergence was followed
by a long period at the surface.

In muskeg areas, where ground movements may spread
out many yards from every step taken, it was found impossible to
approach pools without sending all larvae to the bottom, and
the least movement while observing larvae from the margin of
a pool would interrupt their activities. A conspicuous feeding
habit, especially among tundra species, consists of grazing
along the edges of decaying grasses in the pools. The micro-

flora and fauna of these grasses are being studied.

It is of some interest to record that larvae

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30

isolated in the insectary for individual rearing to associate
last larval exuvium with adult, were invariably slower to
mature than comparable larvae which were reared together under
otherwise identical conditions.

The larvae of the chaoborine species appear to be
the most important predators on Aedes larvae, consuming large
numbers of these in the insectary. These predators also feed
on fairy shrimps, and are in turn fed upon by the larvae of
dytiscid beetles. A fairy shrimp has been taken from the
prehensile antennae of a Chaoborus larva which was itself held
in the mandibles of a larval dytiscid.

3.1.2. Emergence and Mating:

In insectary rearing, mortality at emergence is
considerable, and is higher among females than among males.

The reasons for this are unknown, but contributary factors
may be the unnatural amount of illumination from the sides
and below; perhaps the abnormal stimulation of the pupa to
activity which is difficult to avoid during collection and
transportation, has a devitalizing effect.

The first interest of the newly emerged adult of
all Churchill species of Aedes appears to be mating. This
takes place shortly after emergence, and no species has been
known to take a blood meal before mating. The typical mosquito
mating swarm has been observed for most species, and these
observations follow:

A. nigripes at 1.15 p.m. on July 3, 1947, over the

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31

tundra between a narrow belt of scrubby spruce, and the camp
buildings. The mosquitoes occurred in dancing clouds around
the perimeter of a small shallow lake, the swarms extending
about 3 - 9 feet above the ground.

A. punctor a few feet above the Hudson Bay Railway
tracks, in the forest near Warkworth Creek, after sunset (10.30
p.m.) on July 13, 1947. Also over the tundra near woods east
of Churchill, at 4.0 a.m. (ten minutes after sunrise) on
July 25, and also in 1948, together with -

A. communis forming one enormous swarm stretching as
far as the eye could see as a dark cloud over the Hudson Bay
Railway track at Warworth Creek, and following round the bend
in the track. This swarm persisted from 8.30 until 9.0 p.m. on
the evening of July 16, all individuals heading in the same
direction at any one time, sometimes north and sometimes south,
but always along the railway track, and extending from a height
of 3 - 10 feet. There was no wind at this time; the air temp¬
erature over the track was 62°F, that over the vegetation on
either side 58°F; saturation deficiency decreased from 4.3 to
3.7 mms. of mercury, and light intensity remained at about
650 lumens per square foot. Cloud was 4/lOths, and the sun
set at 9.45 p.m.

A. excrucians over open tundra at 9.30 p.m- on July
12, temperature 61°F, saturation deficiency 2.5 mms., wind speed
5 m.p.h., light intensity 90 lumens p. sq.ft.

A. campestris in rather small swarms over a forest
clearing at Warkworth Creek, at a height of 6 - 12 feet at 8.30
p.m. on July 16, 1948. Weather data as in note on A. communis.

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32

Further evidence of the remarkable temperature
sensitivity shown in these notes was obtained 2 hours after
sunrise on July 17, when both mosquitoes and blackflies were
seen to select the charred vertical surfaces of tree stumps in
a burnt off area as resting sites. The greater absorption by
these surfaces had raised their temperature 2 Fahrenheit degrees
above the normal tree trunk.

3.1.3. Adult Feeding and Activity:

Mosquitoes having mated, man has no longer any
practical interest in the male mosquito, but becomes increas¬
ingly interested in the female. It is well established that
many mosquito species can lay viable eggs without a blood
meal (9,30,50), although the number may be reduced, and this
is probably true for most of the Churchill species. Certainly,
as the season progresses, the majority of the mosquitoes which
are attracted to man are carrying eggs of some description,
although it is unlikely that many of them have fed on blood.
Attempts were made in 1943 to obtain mosquitoes freshly fed on
the blood of animals other than man for precipitin tests; no
such specimens were secured up to the end of July. A list of
birds and mammals seen in the area is given as appendix A;
except for the white whale, the mammals are all exceedingly rare
during the fly season, the commonest being mice and lemmings
which spend most of fly time either under ground, or in water.
There is no evidence that the cycle of lemming abundance is
reflected in mosquito abundance. Nestling birds, and the few
amphibia have been watched, but mosquitoes have not been seen to

■ i :*f oiiJ lo eoasbive

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‘

33

feed on these; again, possibly because the observer is
preferred. Longstaff (72) reports A. nigriues feeding on
the redpoll and perhaps the arctic hare in Greenland, and
Thienemann (33) records A. punctor and A. communis apparently
feeding on Microtus and lemmings.

In most individuals of all mosquito species collected
on July 17, 1948, development of the eggs had scarcely begun;
in one specimen of A. campestris eggs could be detected, and in
one of A. communis about 50 developing eggs could be counted
in each ovary. Further dissections on July 26 revealed
considerable progress in development, although eggs were still
far from ready to be laid. A total of 170 eggs could be
counted in specimens of A. punctor, and 300 in A. excrucians.
Captive specimens of A campestris, given a blood meal in the
insectary a few days previously, laid eggs on wet cotton on
July 25 and 26.

Nectar feeding appears to be a universal habit in
Churchill mosquitoes, and here, circumstantial evidence has
been kind. The very common woodland orchid Habenaria obtusata
Pursh., as previously reported by Raup (45), is apparently
normally pollinated by mosquitoes, which pick up one or both
of the poliinia adhering to the ventral margins of the eyas,
when visiting mature flowers, presumably for nectar. On
July 24 and 25, 1947, 6 per cent of mosquitoes were found to
be carrying the poliinia of this orchid. A larger sample
collected on July 12,13,16 and 17, 1948, gave the following
figures: total mosquitoes, 1364; number carrying a single

pollinium, 55; number carrying two poliinia, 3. It seems

bl

: . . . i ..

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ooc. • <z ■ ■ xciococ, ‘it •t3*rev;olri enxcica • .1 .1 oo i,

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" ; l

34

reasonable to assume that the probability of a mosquito in
feeding on Habenaria picking up the left pollinium is the same
as the probability of picking up the right pollinium. If
this is so, the probability of a mosquito picking up both
pollinia is the square of the probability of it picking up
a single pollinium, and the ratio .of the number with two
pollinia to the number with one is the same as the ratio of
the number with one to the number which have visited the
orchid. Working on this assumption, it may be stated that
no less than 74 per cent of the Churchill mosquitoes attracted
to man at the middle of July had fed on Habenaria obtusata.

This is a remarkably high figure when it is considered that
there are numerous other flowers secreting nectar accessible
to mosquitoes at this time. Among these may be mentioned
Rhododendron laoponi cum L., Ledum palustre L. and Dry as
integri folia Vahl., all of which are extremely abundant, and
on all of which, in spite of the difficulty of so doing,
mosquitoes have been observed resting, and apparently feeding.

Pollinia of H. obtusata have been found on all the
species of Aedes except A. cinereus, the proboscis of which
is less than 2 mm. long. They have not been found however
on the small individuals of A. communis.

On two occasions mosquitoes have been observed feeding
on Habenaria hy oerborea L., and figure 7, paid for with no
small amount of blood, shows A. punctor preparing to feed on
this species. Neither the pollinia of this, nor those of
other common species of orchid, however, have been found
attached to mosquitoes.

; t vj .v..- o j ' J ■ a .(j' ■, a i . ■ - r< a: \ '

■

'

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a': a: .a' aa; a. a' aain . L a: : aa

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- :: * \afloc r a; a . ■: a: ■ b ■ . a

. e&cSl,: . ■ . a. 1 J' a ••

■■ v ‘ ■:

35

Figure 7: A. punctor preparing to feed
on Habenaria hyperbore. a.

36

Captive mosquitoes of various species feci readily
on sugar solutions of a wide range of concentration in the
laboratory. The process of feeding, however, was much slower
than feeding on blood, and the quantity consumed at a single
feed was never comparable to the size of the normal blood
meal.

Observations on mosquitoes feeding on blood are
manifold, and need not be prolonged here. Some figure obtained
for weights of blood meals are, however, given in Table 1,
since these figures are used in flight range calculations
in section 3.1.4. The figures for A. stimulans were obtained
at Edmonton, using a chemical balance; the remainder at Churchill,
using a mi cro -dynamometer improvised from glass capillary
tubing, and calibrated by subdividing sheets of bond paper.

Many of the preceding observations and data were
secured during the course of 24 hour collections, in which
2 or 3 observers recorded local weather conditions, collected
biting flies and made notes on their activities at hourly
intervals throughout a 24 hour period. Further data from
these collections are given here, since most of them pertain
to mosquitoes.

In 1947 a preliminary 24 hour collection was made
in order to investigate the possibilities of this method of
working. Equipment and personnel were inadequate, but in
spite of this, useful data were obtained. Two sites were
selected about seven miles east of Churchill camp and a mile
from the shore of Hudson Bay. The first of these (military
map reference 024047, figure 23) was in open tundra meadow,

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37

TABLE 1. The body weights and weights of blood meals consumed
in milligrams, for various species of mosquitoes.

— 1

i

A. stimulans

r 1

A. communis

—j

A. punctor

| Weights of
unf ed

! individuals

1.4, 1.2, 1.5,
x. 3, 1.4,

1.7, 2. 0,1. 6,
1.8, 1.7,

4. 4, 5.1, 4. 7,

4. 4, 3.1,b. 7 ,

Mean unfed
wei ght

1.4

1.8

4.6 !

i Weights of
fully fed

I individuals

3.3, 3.0, 3.0, .
2. 2, 3. 6,

4. 8, 4. 6, 4. 9,
4. 5, 4. 7,

7. 8, 8. 2, 7.1,

6. 9, 7. 3,

1 Mean fed
weight

3.1

4.7

7.5

! Mean weight
of

blood meal

1.7

2.9

2.9

Meal weight

body wei ght

1.2

1.6

p . . — —* ■ — ■ — “ — —j

0.63

1

- bode Mo bm aJri l:e\v vbeef eoj; .1 atiUAT

■ ■ ■■■ ■ •• . ' v 01 t j ; /

. T ~

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O - t ,

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'

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o J u:- IV kh ui \

,

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■

, . . .

'

Figure 8: A. neareticus feeding on man;
stage one, minutes.

Figure 9: A. nearcticus feeding on man;
stage 2, 2j minutes.

39

just to the lee side of a small clump of spruce, and is
illustrated in figure 10. The second (025045) was in a wooded
area about 200 yards south of this, illustrated in figure 11.
Figure 12 shows the nature of the surrounding country.

The first collection was made at 4*00 p.m. on July
24, and the last at 3.00 p.m. on July 25th. Insects were
collected at each station math a tube off the person of the
observer so long as the light was sufficient, and by sweeping
with a net through the cloud of insects on the wing around
the observer. Temperature and humidity readings were taken
every hour, and periodical observations of cloud conditions,
light values, and wind were made.

The observations appeared to indicate that the
outstandingly important weather factor in relation to general
biting fly activity is wind, writh temperature second in
importance, but only below a definite limit, which for
mosquitoes is certainly appreciably below 50°F. Mosquitoes
appear to be indifferent to light intensity. These conclusions
are in agreement with the generally accepted idea of relief
from biting flies obtained along the sea shore, where the
overall wind is fully effective, and where it is supplemented
twice daily by local ‘land and sea breezes'. Mosquitoes
appeared to exhibit some tendency to collect into groups
of trees and patches of wooded country after sunset.

In 1S48 two 24 hour collections were made, one on

the tundra at the site used in 1947 on July 12 - 13, and one
in the forest at Warlcworth Creek on July 16 - 17. Some of
the data from these are presented in graphical form in figures

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■ . . I d I v.

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40

Figure 11. The wooded collectiug site

41

Figure 12: A general view of the 24 hour
collecting area.

42

13 and 14. In these graphs the black columns represent a
measure of the mosquito interest in man, and are computed
arbitrarily from the biting rate and alighting rate figures.
Biting rate figures represent the number of mosquitoes
engaged in feeding during the second minute in which a forearm
is exposed on the lee side of the body. Alighting rate is a
count of the number of mosquitoes alighting on the front of
the trousers between side seams from waist to knee, in the
second minute of standing still, facing downwind. Open columns
represent the proportion of the sky covered by cloud, and the
broken and solid lines represent temperature and saturation
deficiency respectively. The heavy line at the top of each
graph represents the hours of darkness; records commenced
between 10 and 11 a.m.

The tundra graph shows remarkably good correlation
between cloudiness and mosquito interest in man, a fact which
has been previously observed by Hunter (71) . There is a rough
peak of activity shortly after nightfall, when both temperature
and saturation deficiency were falling rapidly. In the forest
graph, as would be expected, the correlation with cloudiness
is less well marked, and there are two quite well defined
peaks of mosquito interest, one shortly before sundown, and
a second shortly after sunrise. Again, no inverse correlation
with saturation deficiency is shown, biting rates often remain¬
ing surprisingly high at high saturation deficiencies. It is
interesting to note that quite high biting rates were recorded
at temperatures below 7°C; Mellanby (40) records the flight
threshold of A. pun c tor, a dominant species in this collection,

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-

Figure 13: explanation on p. 42

43

MOSQUITO ACTIVITY
AND WEATHER

Figure 14: explanation on p. 42

44

45

as about 10°G in Lapland. Wind speed throughout both of these
24 hour periods was low, so that no confirmation of 1947
observations w as obtained, except as regards the absence of
any direct effect of light intensity. These data do not
support the statement of Matheson (37) that all our far northern
Aedes species are primarily diurnal. Further data are required
before much specific variation in activity will show up, but
an examination of the material taken at these collections
reveals that A. cinereus is restricted in its biting activity
to a few hours before sunset, and again after sunrise.

3.1.4. Flight Range:

The difficulties of measuring the flight range of an
insect by the normal method of releasing marked individuals and
recording the distance to the point of recapture, increase in
proportion to the square of the flight range, and are immeasur¬
ably further increased over terrain such as that at Churchill,
where the observer's own power of movement is very restricted.

It is generally accepted that the more northern mosquito
species have a very considerable range of flight, so that a
new approach to this problem had to be found.

The flight range of mosquitoes determines the area
over which it is necessary to kill larvae to ensure protection
from adults for a given locality. This is its primary practical
application. Population pressure is a major stimulus to
movement; this cancels out under normal conditions, but is
at its maximum in infiltration into an area cleared by insecticide

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46

spraying. It follows that the maximum possible flight range
has greater practical significance than flight range under
normal conditions.

The normal method of determining flight range
measures actual distances flown, and concludes that the
maximum flight range is not less than the greatest of these
distances. The method used here has the advantage of approaching
the answer from the opposite direction; the maximum flight
range which is theoretically possible being determined, it
may then be stated that the flight range is not greater than
this figure. Unfortunately it can only be applied to
uninterrupted flights. Flight range data based on distances
from known breeding grounds at which adults are captured are
always open to suspicion in that there may be unknown breeding
grounds, or that adults may have been carried by their hosts or
by man’s vehicles.

The method used is to determine experimentally the
stomach capacity of the insect, the composition of its normal
food and hence the energy obtainable from this by respiratory
processes, the mass of the insect and hence the energy required
to keep it airborne for a given time, and finally the wind
resistance at various speeds and hence the energy required to
travel unit distance. From these data a simple equation can
be obtained for any air speed, solution of which will give the
range at such a speed. The solution of a series of such
equations enables range to be plotted against air speed, the
resulting curve showing a single maximum range. No account
has been taken of the energy stored in the fat body , and

&

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47

elsewhere in the newly emerged adult. This is small in
mosquitoes and is probably largely exhausted in mating and
preliminary feeding activities. It has necessarily been
assumed that the wind resistance of the stationary wings is
the same as that of the wings in motion.

Only a preliminary exploratory application of this
method, using A, ounctor has been made so far, but the results
are sufficiently promising to justify further work, and are
reproduced here:

A. Stomach capacity: It is true that mosquitoes do not normally
engorge on nectar, the food presumably used for migratory
flights, to the extent that they do on blood. On the other
hand there is no evidence that migratory species before setting
out on a long flight do not do so, and, since a maximum figure
is required, stomach capacity has been taken as the space
occupied by a blood meal of mean weight. Taking the specific
gravity of human blood to be 1.06 (53), the figures in Table 1.
show this to be 0.00274 ccs.

B. Food composition and energy per meal: Samples of nectar

from Rhododendron lapponi cum which is believed to be utilised
by mosquitoes were collected at Churchill at 3.0 p.m. on July 1
by means of glass capillary tubes, and sealed into these. The
amount obtained from a single flower was very variable, ranging
from 0.00011 ccs. to 0.00088 ccs., but the 0.00274 ccs. required
by A. punctor wrould-be readily available from a single plant.
Subsequent analysis showed this nectar to have the following
composition: reducing sugars, 48 per cent; non- reducing

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■ : io| .

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48

sugars, 41%; other matter not estimated, including water,

11 per cent.

Assuming the reducing sugars to be mainly glucose,
with a heat of combustion of 673 kgm. cals, per gm. molecular
weight, and the non-reducing sugars mainly sucrose, for which
the figure is 1349.6 kgm. cals., the energy available in
0.00274 ccs. of this material would be 12.7 calories or

O

5.30 x 10 ergs. Unfortunately little is known of the efficiency
with which the insect can transform this chemical energy into
mechanical energy, but it may be assumed that this is not
much less than that of a mammal such as man (6 3), for which
an average maximum is 25 per cent (54). This would give
1.325 x 10 ergs available for flight. Still less is known of
the efficiency with which insect wings can translate this
muscular energy into f onward aerial motion, but since the main
loss here is in the form of kinetic energy of the slipstream,

O

this is probably not more than 10 per cent, leaving 1.193 x 10
ergs of useful energy available.

C . Insect mass and energy required to remain airborne : Since
the rate of loss of mass depends on the rate of consumption of
energy, which in turn depends on the mass at any particular
instant, the solution of a differential equation should be
used here, but in a necessarily approximate preliminary
investigation, sufficient accuracy is obtained by assuming
that the mass remains constant at its mean value, which from
the figures in Table 1. is 0.00605 gms. The energy required
to remain airborne is equal to the rate at which gravity would

'

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.

.

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■ •- ■ : • . S ; . r :,r; x o " ' ’

49

p

do work on the insect; this is 0.00605 x 981 or 2910

2

ergs per second. That is, A. pun c tor on a. meal of this
nature could remain airborne, without forward motion for

o

1.193 x 10° minutes, or 11 hours 20 minutes.

2910 x 60

D. Wind resistance at various speeds; This was measured with
the aid of the micro -dynamometer referred to insection 3.1.3.

The instrument was set up with the glass capillary vertical,
with the free end below dipping into a cell built on to the
side of the scale and containing a glycerol-water mixture
of suitable viscosity to damp out vibrations. Adjacent to it
was a portable anemometer, and at a variable distance from the
two instruments, a 110 volt 1 ampere table fan with 16”
diameten rotor, and a three stage resistance speed control.

The apparatus was first calibrated by taking a series of
corresponding readings of wind speed on the anemometer and
deflection of the dynamometer, and plotting these against each
other. A specimen of A. ounctor half fed on blood, recently
killed and set in flying attitude, was then mounted with the
load position of the glass capillary at the side of the
mesothorax, and the readings were repeated. The curves
obtained after converting the dynamometer deflections to dynes
and the anemometer readings to metres per second, are given
in figure 15, and enable the wind resistance at any desired
speed to be read off.

At an air speed of 0.5 metres per second (1.12 m.p.h.)
the wind resistance is 1.0 dynes. Supposing the range to be
R metres, the time in flight will be 2R seconds. The wTork

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Figure 15

50

~i r

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S £ 2 t

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SPEED IN METRES PER SECOND

51

done in remaining airborne will be 2910 x 2R ergs, and the
energy used in forward motion will be 1.0 x R x 1000 ergs.

The sum of these two must, equal the total energy available, i.e.
1.193 x 10' ergs, and the solution of this equation gives R

o

the value 1.193 x 10 metres. This is 17,500 metres or about
6820

11 miles- Similarly the following figures may be obtained:

At 1.0 metres per second: 23,400 metres.

At 1.5 metres per second: 22,300 metres.

At 2.0 metres per second: 17,700 metres.

At 2.5 metres per second: 9,400 metres.

(5.6 m.p.h.J

By plotting these figures on a graph (Fig. 15) it
is seen that the maximum possible uninterrupted flight range in
still air for A. punctor is not greater than 24 kilometres.

A. punctor is not regarded as a migratory species.

3.2. On the Biology and Behaviour of Blackflies.

Studies on the immature stages of blackflies have
been impeded by the difficulty of laboratory rearing, except
for pupa to adult, and by the impossibility at present of
identifying any stages earlier than the late last larval
instar.

Observations have been made on the hatching of eggs,
which from the subsequent abundance of S. venus turn in the
stream from which they were collected, presumably belonged
to this species. Like many insect eggs, these darken as they
mature; this is brought about partly by pigmentation in the

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52

chorion and embryonic integument, and partly by the development

of a prominent blue-black hatching spine on the vertex, and

two dark eyespots on either side of the head. The front of

the

the embryonic head fits closely into/ apex or smallest angle
of the egg, which in dorsal view has an unusual rounded
triangular shape. The thorax and abdomen are coiled into
an S-shape and fill the remainder of the egg. Contractile
waves in the abdomen, movements of the mouthparts, and partial
rotations of the head, which apparently scratch the chorion
with the hatching spine can all be observed prior to eelosion.
The chorion eventually ruptures in such a manner as to allow
the small angle of the triangle to hinge open, and the active
young larva to emerge head first; the whole process, from the
first appearance of the split, occupying about 20 minutes in
the laboratory.

These eggs are nearly always found in a very
characteristic situation. Where sedges are bent by the current
so that the top portion of the leaf lies parallel to and just
below the surface of the stream, the eggs of this species
will be found cemented to the upper side of the leaf within
an inch or so of its tip. The mechanics of oviposition in
such a situation are readily comprehensible. The egg just
prior to hatching, and a typical oviposition site are shown in
figures 16 and 17 respectively .

Fish feed readily on blackfly larvae. As many as
71 larvae of all ages have been taken from the stomach of a
sucker (Gatostomus sp.) from a sparsely infested creek, and
73 very young larvae from the stomach of a stickleback (Pungi tius

.

> r\; '■ ,* HO 'IS V H X J ■ H O' ; S'X+'.JL.

. , ' " .. , ■

.

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o j

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.

; rr.;.

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53

Figure 16: A mature
egg of S, venus turn

54

uungitius) from a stream which observers bad reported to be
free from infestation. Larvae have also been found in the stom¬
ach of the northern wood frog, and of jackfish; in the latter
animal they were apparently ingested incidentally along with
a mat of filamentous algae to which they had been attached.

Very little is known of the mating and feeding habits
of adult blackfiies. Bn si mu li urn species A resembles E. lascivum
in that it mates freely on vegetation at the sides of the
stream from which it emerged, on the clothing and person, and
even in the collectors vials. The only other Churchill species
of which the mating habits have been observed is B. au reurn, of
which a pair was taken off the clothing, in copula, at 11.0 a.m.
on July 17 in the woods adjoining the creek in which the
species develops.

S. venustum is the only species which is a serious
pest of man at Churchill; this species takes rather longer to
feed than do mosquitoes, but in spite of its smaller size it
takes almost as large a meal, weights of 2.4 and 1.7 mgms.
having been recorded.

There are some indications that with the exception
of S. arcticum, the blackfiies do not travel far in search of
a blood meal. Of 265 blackfiies taken during the 1947 24 hour
collection, only 2 or 0.7 per cent were S. vittatum , the
breeding of which is believed to be confined to the Churchill
Paver, nine miles west of the collection site. Critical light
values for blackfly flight and feeding recorded during the
1948 24 hour collections were as follows: cessation of biting,
tundra 900 lumens per sq. ft., forest 500; cessation of flying,

: a:0 i. a :aa

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55

tundra 900, forest 500; resumption of flying, tundra 1800?
forest 1250; resumption of biting, tundra 1800, forest 1750
lumens per sq. ft.

3.3. Biology and Behaviour of Tabanids.

The abundance of certain tabanid species leads to
speculation as to the larval food material, line (29) success-
fully reared a number of species of Hybomi tra on small Crustacea
and on earthworms, both living and dead. Stone (56) was able
to repeat this but found mosquito larvae to be the best food
for the young tabanid larvae. It would seem possible, therefore,
that the enormous numbers of mosquito larvae stranded from
drying pools may form a material element in the diet of one
or more species of Hybomi tra.

Larvae in the insectary in 1948, species as yet
unknown, fed avidly on small gastropods, and the presence of
empty shells of this snail in the field provided a guide to
the whereabouts of larvae. The cannibalistic habits of these
larvae probably explain their very scattered distribution,
which makes them very much harder to collect than the abundance
of adults would lead one to suppose. The chemical treatment
recommended by Bailey (7), but with Triton X-100 replacing
sodium lanryl sulphate, and a trade preparation sold to anglers
for bringing worms to the surface, were used extensively in
1948 without revealing anything but extremely sparse larval
populations, Cameron (13) states that Chrysops larvae will
not feed on living animal material, but Waterston (84) reports

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56

them as preying on mosquito larvae, under laboratory
conditions .

The few instances of mating observed took place
at various times of day. H . gr aci li p a.1 pi s seemingly mates
as a rule about the middle of the morning. Females at least,
apparently feed on flowers soon after emerging; most of the
earlier specimens taken of nearly all species, were liberally
dusted with pollen. Specimens of Chrysops mitis were collected
off flowers. Specimens of H. affinis fed readily on various
concentrations of sugar solution in the laboratory, but
would not take expressed human blood; the piercing procedure
is presumably necessary to condition the insect for blood
feeding.

The effect of a meal of human blood on egg
development in H. affinis is astounding. Specimens collected
in the field on July 20 had very rudimentary ovaries, the
abdomen being very largely filled with air sacs, and no eggs
discernible. One of these given a full blood meal, and killed
three days later y/as found, to have the abdomen swollen, and
filled almost to bursting with well developed eggs. The
number of these was estimated at 600.

With the exception of H. affinis and H. seotentrionali s
the adults of no species of either genus were found in numbers
more than a few hundred yards from woodland; this was especially
true of the Chrysops species which were seldom taken outside
of the woods.

The adults of several species of Hybomitra, H. affinis
conspicuous amongst them, are attracted in large numbers to

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57

vehicles, including trucks, trains, and aircraft. Large
numbers of flies would collect around a vehicle (Fig. 18) while
an observer standing a few yards away might pass practically
unmolested. Stone (56) suggests that they are attracted by
the movement, but adds that they will collect around a
standing automobile. This fact was also observed, but in every
instance it was around a standing vehicle which had been in
motion, and was warm in consequence. Warmth appears to be an
attractive factor, while movement stimulates pursuit. Certainly
it is of no use attempting to run, or even to drive, away from
tabanids over the terrain around Churchill. Specimens which
appeared to be H. af finis were observed to lose ground only
slowly when in pursuit of a train travelling at approximately
30 m.p.h. On the morning of July 12, 1947, and a few days
subsequent to this, several observers reported a caribou calf,
apparently separated from the herd, careering madly around the
Churchill locality, pursued by a small cloud of tabanids. The
animal appeared in very poor condition, presumably as a result
of the attentions of the flies. Chained dogs, however, were not
seen to be attacked by large numbers of tabanids, possibly on
account of their inability to run away.

Activity, and especially biting activity, of tabanids
is far more influenced by weather conditions than is that of
mosquitoes. In cool, damp, overcast and windy weather few, if
any tabanids are seen on the wing. The weather factors of greatest
importance seem to be temperature and sunlight; high relative
humidity appears to be associated with absence of biting only
secondarily, by virtue of its association with low temperature.

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5

Biting was rare at temperatures below 55°F, and even above this
temperature would not normally occur unless there had previously
been an appreciable period of sunshine on the same day. The
well established preference "of tabanids for biting through
wet skin (57) was. confirmed by the observations of personnel
working in biackfly streams, and by bathers. When up to the
neck in water, H. septentrionaLis especially, will circle the
head continuously at a distance of about a metre, coming in to
bite as soon as the rest of the body is exposed.

During the 1947 24 hour collection, tabanids were no
longer on the wing about half an hour after sunset. The
temperature at that time fell below 65°F. and the light value
below 500 lumens per sq.ft. Activity was not resumed until
two hours after sunrise, when the temperature was 55 °F. and the
light value 2000 lumens p. sq.ft, A . af f i ni s was the most
persistent species in each instance, but possibly only apparently
so, on account of its greater abundance. These observations
were confirmed during the 24 hour collections in 1948.

4, THE INFLUENCE OF BITING FLIES ON MAN
AND ON HIS ACTIVITIES

/

There are many reports, some authentic, some otherwise,
of individual men and animals being killed by biting flies, either
directly by loss of blood, or indirectly through the reaction
to toxic materials injected. There is no doubt whatever but
that current methods of protection - protective, or even normal
•sensible1 clothing, and a modern repellent - can entirely
eliminate such occurrences without undue expenditure of time,
effort, or materials. There remain, however, very considerable
discomforts and delays, risks of secondary infections, and in
susceptible or sensitized persons reactions to toxic materials
which not infrequently require hospital treatment. In a really
intense blackfly and mosquito population, even conversation
becomes difficult unless one is prepared to swallow many of the
insects. Finally, there is another effect of biting fly attack
which has not been fully considered in the past, a psycho-
physiologi cal effect. This was clearly demonstrated on several
occasions at Churchill, in particular during the camp at Warkworth
Creek in 1947, and during the 24 hour collecting camps.

4.1. Physiological Influences.

As opportunity offered, observations wrere made on the
reactions to bites of both mosquitoes and bla.ckflies, with the

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61

object of confirming for the species encountered here, the
accepted opinions that: repeated bites result in a degree of
immunity, and that the reaction is less if the insect is allowed
to feed to completion (47). Observations were not sufficiently
numerous for definite conclusions to be drawn, but what evidence
there is tends to support these views, and this evidence is
recorded here:

Mosquitoes: Culiseta alaskaensi s Ludl. June 18, just above elbow,
fed to completion in 2% minutes. Feeding was
preceded by a preliminary probe from final puncture.
Irritation was possibly slightly greater at the trial
puncture. Symptoms just detectable after 30 hours.

Aedes excrucians. July 17, partial feeding inside
right knee. Considerable irritation directly after
biting. After 9 hours a small reddish weal, very
slight irritation. 24 hours, no symptoms detectable.

A. ni gripes. July. 17, complete feeding 2” above right
knee. Some irritation during feeding and for a few
minutes afterwards. After 8 hours slight hardness,
small reddish weal and very slight irritation. 24
hours very slight irritation, faint reddish mark.

A. ni gripes. July 17, complete feeding 1M below elbow.
Slight irritation during feeding. After 6 hours no
detectable symptoms.

A. ni gripes. July 17, partial feeding upper left
forearm. Slight irritation during feeding; after

4 hours slight reddish weal and slight irritation.

After 18 hours no symptoms detectable.

Blackflies: Four bites of S. venus turn were observed on July 17.

At the first two of these, the insect was allowed to
feed to sateity, at the other two the insect was
removed shortly after starting feeding.

1. Below and inside right knee. Feeding time 5 minutes.
After 4 hours slight swelling and moderate irritation.
After 14 hours no swelling, slight irritation. After

3 days slight irritation but no other symptoms. After

5 days, no symptoms.

2. Outside left leg, 4U above ankle. Very slight
irritation immediately after bite. Swelling appeared
after 4 hours, l-|n across, irritation considerable.

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62

After 14 hours no swelling, but still some irritation.
Slight irritation after 3 days, none after 5 days.

3. Outside left leg, 12" above ankle. Irritation
considerable and continuous from1', time of bite onwards;
a hard lump around puncture. After 5 hours swelling
about 3" across and irritation severe. After 14 hours
swelling slight and moderate irritation. After 3 days,
no swelling but moderate irritation. Appreciable
irritation remained after 5 days.

4. Outside right leg, 4" below knee. Symptoms as for
No. 3 but somewhat more severe.

There was no sensation of pain during piercing; in
each instance the insect crawled down through the
hairs and held itself practically perpendicular to
the skin surface. There was a slight flow of blood
from all four bites for a few minutes after feeding
ceased.

Concerning the direct effect of loss of blood, a simple
calculation on this is of interest. The highest mosquito biting
rate recorded at Churchill during 1947-8 was 160 bites per
minute. The total skin surface is about 33 times that of the
forearm, so that a completely unprotected man (materials often
used for summer clothing give very little protection against
northern species) could receive a maximum of 5290 bites per
minute. At 2.5 mgms. per bite (see Table 1.), the blood lost
per minute would be 13.2 gms. The symptoms resulting from a
loss of 50 per cent of the blood are certainly severe enough (64)
to prevent the victim from progressing any distance across the
Churchill terrain. Assuming that the blood composes 7.7 per
cent of the body weight, and has a specific -gravity of 1.06 ( 54),
this situation could be reached in about three hours on account
of mosquitoes alone. Although the biting rates for blackflies
and tabanids are both much lower, the loss of blood from their
larger punctures, in which an anticoagulin is present, would
contribute materially to exhaustion from this cause.

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63

In so far as the irritation caused by mosquito bites
is concerned, Macloskie (35) regarded the middle lobe of the
salivary gland as the source of the poison concerned, Hi ley and
Johannsen (47) refer to the work of Schaudinn (49) and of Roy (48).
Results appear to be based on Anopheline species only, and to
demonstrate somewhat inconclusively that irritation is due to
an enzyme produced by constant commensal fungi (yeasts ?) living
in the oesophageal diverticula. The results of Cornwall and
Patton (16) seem to support this view, and Imms (31) quotes
Kindle, also in support of it. Bruck (12) however, extracted
a toxin which he named culicin from the bodies of mosquitoes
and assumed this came from the salivary glands, and McKinley (39)
has demonstrated convincingly the presence of a poison in the
salivary glands of Aedes aegyoti . hone of this work relates to
northern species of Aedes; I have not had access to the work of
Hecht (28) who is reported to have summarised the information
available in 1928.

With regard to the situation in blackflies, Patton and
Evans (41) figure the alimentary system of S. ornatum with a
single oesophageal diverticulum, and suggest a toxic enzyme in
the saliva of some species as the irritant. Both in 1947 and in
1948 the reaction to blackfly bites diminished markedly as the
season progressed; this has been regarded as the development of
a temporary immunity as a result of bites received. In view of
the very different environmental conditions under which the later
generations of blackflies develop, however, this could equally
well be attributed to a physiological difference in these
generations of blackflies. This appears to be all that is known

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64

on the subject, although, at least to the susceptible newcomer,
the toxic effect of the blackfly bite is undoubtedly the most
potent weapon in the whole biting fly armoury. It is believed
to be this toxic material which is the cause of numerous deaths
of cattle in Saskatchewan when attacked by S. arcticum (46).

Typical reactions to the bites of mosquitoes and of
blackflies are shown in figures 19 and 20 respectively.

Observations on the bites of tabanids are few; these
insects are so clumsy over piercing the skin that they rarely
get away with a complete meal from man. As a group, they do
not appear to have ’learnt1 yet that man has hands, and it is
usually a biological error for a tabanid to attempt to secure
a meal from man. Considerable personal variation in liability
to attack has been noticed. The species of Chrysops appear
to bite man more freely than do Hybomi tra, but none is a serious
biter of man when he is protected by suitable clothing and a
good repellent.

Tabanids gain access to buildings in considerable
numbers, but cause annoyance there more by their efforts to
get out again than by any attempts to bite. In fact , no instance
of a tabanid biting indoors has been recorded at Churchill.

4.2. Psychological Influences.

The psychological effects of biting fly attack seem
to result partly from the immediate stinging sensation of the
insect mouthparts, partly from the manual ’removal reaction’
to this, and partly from the continual impact of insects on
the face and person. Given equal numbers, tabanids are regarded

Figure 19: A typical reaction to the

puncture of a mosquito in a
susceptible individual.

Figure 20: A typical reaction to
blackfly punctures.

66

as the most important group in relation to each of these
three factors, followed by mosquitoes and finally blackflies.

The two genera of tabanids however, are very different in their
effects. 'The Chrysops species contribute to the psychological
menace mainly by virtue of their rather silent approach and
furtive alighting, Hybomi tra species on account of their
swift and noisy flight, and the momentum of their impacts
on the person.

The typical 'removal reaction' is illustrated in
figures 21 and 22. It might be supposed that this, along with
the first factor, could be eliminated by protective clothing
and repellents, but such is not the case; the reaction may
be evoked by insects alighting, but not biting, or even in
certain circumstances by non-existent insects.

The combined influence of these three factors presents
a more serious problem in our present state of knowledge than
the problem of direct physiological effects. This combined
influence would, it is believed, also prove far more serious
in military operations, causing as it does, a serious reduction
in individual efficiency, and an even more serious lowering
of group morale. Carried to the extreme, it is considered
that the susceptible individual would become a liability
rather than an asset from these causes sooner than from direct
physiological effects; the rapidity with which such a person
can become worked up into an emotional state bordering on
dementia as a result of the continually accelerated and
increasingly ineffective removal reactions, has to be seen
to be believed.

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(white whale in foreground).

Figure 22:

The removal reaction (2).

68

More knowledge of this problem is required before
definite solutions can be proposed; it is possible, for instance,
that the effects may be very different in a large body of men.
Tentaive proposals for combating these factors are given in
section 5, and improvements in these methods of personal
protection will certainly play their part.

4.3. Indirect Influences of Biting Flies.

None of the Churchill species of biting flies is
known to serve as a true vector for any disease or parasite
of man in the Churchill area. The possibility of mechanical
transmission of disease by biting flies is also remote at
present, in view of the very sparse human population, and the
resulting extreme Improbability of any individual insect taking
blood meals from two humans.

S. venustum however transmits an important disease
of wild and domestic ducks, caused by a proto zoon parasite
Leucocyte zoon anatis Wickware, which is closely related to the
malaria plasmodia (75). The cycle of events in this disease
is comparable with that in malaria, and it may cause heavy
mortality; it has recently been shown, however, that it will
not respond to treatment with anti-malarial drugs (21).

Scott (82) has shown that H. septentrionalis is
capable of transmitting swamp fever or infectious anaemia of
horses, and various ?/orkers (7 9,85) have demonstrated the ability
of the filarial parasite of dogs Dirofilari a immitis Leidy to
develop in A. cixiereus , A. pun c tor, and possibly A. flavescens
and A-. excrucians. Tularaemia and Plasmodium gallinaceum have

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also been transmitted experimentally by H . s ep t ent ri onali s
(76) and A. cinereus (74), and by A. campestris (65) respect¬
ively.

Although horses have been maintained at the extreme
point of the Churchill peninsula. , where the full benefit of
sea. breezes is obtained, in general the larger domestic
animals are excluded from the area on account of biting flies.
Most caribou move out northwards along the shore line, before
the flies emerge; the Churchill butcher reports that animals
from the forest can be distinguished at once by the presence
of bites all over the body, the bites on those from the tundra
being concentrated near the feet, presumably on account of
wind. Husky dogs endure a miserable existence in fly time,
and attempt to emulate the lemming, burrowing into the ground
to secure a measure of protection.

Further south, mosquitoes are blamed for reduction
in land values, for crop losses through impeding harvesting
operations at the best time, for general loss of working time
on outdoor employment, and for impairment of health through
preventing outdoor recreational activities. Only the last
two of these factors are applicable in northern regions.

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5. EXPERIMENTS ON THE CONTROL OP BITING FLIES

Tnree approaches to the problem of biting fly control
are possible. The first and most obvious method is the
application of chemical insecticides, mainly against the larval
stages. This is the simplest method, cheapest at the start
perhaps, since less fundamental work is required, but probably
most expensive in the long run, since once started it may
bring about conditions which demand its continuation. It involves
a risk of unforeseen consequences. The second is to so alter their
habitat that they will never develop in troublesome numbers;
this may not be practicable, and complete control by this method
would certainly require vastly more knowledge than we have at
present. The third, the safest and perhaps the most civilized
method, is to let them live, but to arrange matters so that
they are kept at a comfortable distance from man, and from
animals on which he is dependent. What particular combination
of these methods is employed will be decided by circumstances.

5.1. Chemical means for the Reduction of Numbers.

Chemical methods for the control of malaria carrying

species are well established. The principle objects of this
work were firstly, to discover what modifications would be

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required in these methods for the control of northern species
of Aedes; secondly, to adapt the technique of preflooding
treatments developed against salt marsh mosquitoes at Orlando,
Florida, for use in the north; and finally to explore the
possibilities of the chemical control of blackflies.

Results of experiments involving the application of
a variety of recently discovered insecticides against mosquito
larvae from ground equipment, give no suggestion that any of
these can compete with DDT, although some of them are no less
toxic.

The preflooding application of DDT on the frozen
ground, or on ice and snow cover offers the following advan¬
tages over normal methods of treatment: movement over the
ground is much easier at this time; DDT has a lower LD 50
for newly hatched mosquito larvae, and DDT has a negative
temperature coefficient of toxicity. In practice however,
much material may be lost from snow drifting and heavy run-off
at thawing, and the enormous areas which require to be treated
dictate application from the air, so that these advantages
are largely discounted.

Results of several experiments on the aerial appli¬
cation of DDT in oil solutions indicate that the dosage
required for the control of Aedes larvae is about 0.5 lbs
DDT per acre, or nearly five times that required for Anopheles
control, and also that very large areas would have to be treated
to secure freedom from mosquitoes for the season at the centre
of the area. This agrees with data on the flight range of
these species.

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Several tests of ground applications of DDT in
aerosol form against mosquito larvae and adults, and tests
of a number of materials against blackfly larvae were made.
Detailed accounts of these experiments follow.

5.1.1. Experiments with the Hochberg-Lamer
Aerosol Generator against Mosquito
Larvae:

Two experiments were carried out in the second half of
June 1947 to investigate the effectiveness of DDT aerosols
against mosquito larvae in the open under the conditions found
at Churchill. Material was dispensed from 500 yard base lines,
and entomological observations were carried out to a depth of
about 600 yards from these. The plot for the earlier experiment
was on tundra meadow, and for the later, on terrain with a heavy
covering of birch and willow shrubs, adjoining a tidal flat.

These areas are marked (1) and (2) on figure 23. The material
was dispensed with an early model of the Hochberg-Lamer aerosol
generator (inventor’s model no. 4) (32) which was mounted on a
tracked amphibious trailer containing the tanks of insecticide
and the fuel for the .generator , and towed behind a snowmobile
(Fig. 25).

DDT was supplied to the generator in the form of an
emulsion of the following composition:

Lubricating oil (equivalent SAE 10) 5 imperial gallons

Xylene 1 ■ r i mp .gals.

DDT 4 | lbs .

Triton X-1Q0 emulsifier 2-J- lbs.

Water 5 "imp. gals.

and this mixture was dispensed at the rate of about 1/3 of a

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Figure 23:

Map shorn ng the location of plots treated with
DDT aerosols.

74

gallon per minute.

Prior to the liberation of the insecticide, dipper
counts of the mosquito larval population at selected locations
were made; these were repeated at intervals after the treatment
and a comparison of the figures obtained was used for estimating
the mortality at varying distances from, §nd to the leeward
side of the line of release of the insecticide. Uo chemical
or physical estimates of the DDT deposited at varying distances,
nor of the droplet size spectrum of the aerosol were made, but
the nozzle temperature was kept at 300 - 325°F. to minimize
the charring which occurred at the recommended temperature of
450°F., and to give a rather coarse droplet size in view of the
prevailing high wind speeds.

Experiment 1, *

The base line for the plot used in this experiment
was set out with ends determined by the map references 917066
and 922065. The sides of the plot ran north and south, and
east and west, as the prevailing winds for a few days prior
to the marking out had been approximately southerly in direction.
The terrain was level tundra meadow, with a large proportion
of the area taken up by shallow and for the most part rather
indefinite pools in which the mosquitoes A. punctor, A. ni gripes,
and A. nearcticus were breeding. The population, although well
distributed was nowhere very heavy. This distribution of water
bodies, -while it greatly facilitated the selection of dipping
sites, proved ultimately, in this particular instance, to render

* This experiment was conducted by Mr. W.C. McDuffie to
whom I am indebted for permission to interpret and
use these results.

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75

the effects of evaporation very serious. A general view of
the area is shown in figure 26.

The plot was being used for breeding purposes by
various birds, chiefly plovers and curlews. These suffered
no direct adversity from the experiment.

Dipping stations were marked out in three equally
spaced lines running north from the base line, and at intervals
of 50 yards from this, the stations furthest from the base
line being at a distance of 550 yards from it. Lines were
numbered 1, 2, and 3, from east to west. The layout of the
plot and the dipping stations is shown in figure 24. 400 cc.

dippers were used, and ten dips were taken at each station at
each population estimate. The average number of larvae
obtained per dip in the pretreatment estimate made on June 16
was 1.06; these were all in the third or fourth instar; the
results are set out in detail in the first group in table 2.

The insecticide was dispensed from 10.0 to 11.30 a.m.
on June 18. The weather was fine, with light cloud; wind BSE,
the recorded speed by anemometer on top of an adjoining ridge
to the east of the plot was 15 m.p.h. ; wind speed at the plot
was appreciably less than this and was estimated at 10 - 12 m.p.h.
The shade temperature during the treatment rose from 58 ~ 63°F.,
and it appeared from the behaviour of the insecticide cloud,
which moved close to the ground and remained visible for a
distance of some 150 - 200 yards, that inversion conditions
xorevailed. The generator was actually in operation for 75
minutes, one stoppage being necessary to change a choked filter,
but for only 48 minutes was the emission actually over the

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Figure 25; Snowmobile with amphibious
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Figure 26; A general view of the area
of experiment 1.

78

observed plot, the remaining time being spent in turning at
either end of the base line. During these 48 minutes, 14 gallons
of emulsion were consumed; this represents a total application
of 5.4 lbs. DDT or 1.08 lbs. per hundred yards of base line.

If it is assumed that virtually all of this DDT' is deposited
within the observed area, the calculated dosage then becomes
0.087 lbs per acre.

During the emission period the generator was towed
at a little over 2 m.p.h.; beginning at the east end of the
base line, three complete round trips to the west end and back
to the east end were made. Walking down wind from the generator,
the smell of xylene could be detected wherever there was visible
cloud. At the end of the emission a distinct oil film was
detectable on the surface of pools up to at least 200 yards
from the emission line; at 50 yards this was so pronounced that
a photograph was secured and is reproduced as figure 27.

A short distance from the baseline, dolichopodid flies ware seen
to be in difficulties on the surface of the water quite early
in the treatment, but towards the conclusion of this, dancing
clouds of newly emerged midges at 400 yards from the base line
seemed quite unaffected.

The first population estimate after treatment was
made approximately 24 hours later on June 19. Weather conditions
remained much the same as at the previous count, except that the
barometer was now falling rather rapidly. The counts obtained
at this estimate appear in the second group in table 2. A
superficial examination of the area showed no conspicuous
reduction in larval population beyond 50 to 100 yards down wind

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TABLE 2. Population estimates and percentage mortalities at
varying distances from the base line.

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Figure 28: A general view of the grassy
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81

from the base line; many living larvae were seen considerably
closer than this, although here there were also dead and
moribund mosquito larvae and dead water beetles and caddis
larvae. At stations 7 in lines 2 and 3, the pools had dried
up to such an extent that it was not possible to take the full
ten dips, and a similar drying up may account for, the capricious
figures at other stations. As expected from the direction of
the wind, mortality in line 1 did not extend appreciably
beyond 100 yards from the base line. There were many pupae in
the counts at this estimate.

A final population estimate was made on the morning
of June 21, 72 hours after the treatment. Weather conditions
were very different; 0.08 inches of rain fell on the morning
of the observations, humidity was much higher, the sky was
overcast, and the barometric pressure still lower than at the
24 hour count. The figures obtained are recorded in the third
group in table 2. and are no less capricious, than those obtained
at the previous count; figures for line 1 were unfortunately
lost in transit. By this time further pools had so dried, up
as to prevent ten full dips being tshen, notably at stations 8
and 9 in line 3; clearly this drying up had not been offset by
the small amount of rain which had fallen. There was a much
greater proportion of pupae appearing in these counts.

The first mosquito pupae taken in the Churchill
area during this season were found on June 16, the date of the
first population estimate. In view of the two day interval
between this estimate and the treatment, the assumption has
been made that some of the pupae appearing in the second and third

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82

estimates had already pupated before the application of the

insecticide. Considering also that the whole experiment took
place during the very beginnings of the pupation period for the
species concerned, it has been further assumed that the
pupation rate throughout the experiment was uniform. Working
on tnese two assumptions, in calculating percentage mortalities
the pupal figures obtained in the post treatment counts were
weighted, each pupa counting as 1/3 of one larva in the 24 hour
count, and as 3/5 of one larva in the 72 hour count. This was
done in order to give a picture of the effect of the insecticide
on the larvae, uncomplicated by the known greater resistance of
pupal mosquitoes. The apparent percentage mortalities given in
table 2 were obtained by this method.

Discussion; It is clear that the dosage employed was too low
to give effective larval control over a useful area, although
the results obtained, in spite of their capricious nature,
definitely represent a serious under- estimate of the actual
mortality.

During the period between the first and second
population estimates, temperatures were high and humidities
low , while wind speeds were moderate to high, and precipitation
was nil. During the day of treatment, the humidity actually
reached the lowest figure recorded during the period of work
at Churchill, and the saturation deficiency reached a maximum
for this same period at 8.S7 mms. of mercury, and was continually
high throughout the period. These extremely drying conditions
would naturally be expected with continual southerly or land
breezes, and operating as they did, for an undesirably long

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interval on highly dispersed water bodies, they clearly
brought about a remarkable concentration of larvae from wide
areas into smaller and smaller pools. Such a concentration
naturally shows itself as an increased apparent population, when
this is sampled by the dipping method. This apparent increase
offset, and in some instances more than offset, the reduction
brought about by the treatment. No other explanation for these
figures can be adduced; first and second instar larvae were
not found.

The very great variation in apparent mortality
recorded at different stations is directly attributable to the
variation in mean depth of the separate pools and water areas.
The fact that apparent percentage mortalities of 54 per cent at
200 yards and 45 per cent at 250 yards were recorded, can only
be explained on the assumption that the insecticide did cause
significant kills; the possible action of predators can be
discounted by virtue of their small numbers here, and the
general absence of any conspicuous reductions in population
due to them in this locality.

The lapse of a further two days between the 24 hour
and 72 hour population estimates allowed further evaporation
to occur, although conditions were not then so severe. That
this is the correct explanation is supported by the following
facts: that there is good correlation between the 24 hour .and
the 72 hour figures, the latter being the more extreme; that
those stations which were nearly dry gave the conspicuously
higher counts; and finally, that some stations had dried up
completely at the 24 hour count, and still more after 72 hours.

.

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84

If the 24 hour count population figures are adjusted
for evaporation on the basis of station 10 line 2, which shows
the highest per cent increase of stations where insecticide
mortality would be expected to be small, the mortalities
shown in the graph, figure 31, are obtained. These are
considered to represent a reasonably close approximation to the
true figures.

On the basis of the results obtained in this
experiment, it was decided to run a second experiment at a
higher dosage, allowing a smaller time interval between
population estimates, and particularly between the pretreatment
estimate and the treatment.

experiment 2.

This experiment was run from a base line between
the map references: 891083 and 896081. As it was proposed to
release the insecticide on this occasion in the evening, and
the wind on the three previous evenings had been SE and SSE,
the base line was marked out on a bearing of 5 5°, and 600 yard
side lines were marked out from either end of this. The
terrain here was flat, with numerous discrete pools, which
were rather scarcer towards the higher, shoreward, or eastern
boundary. The central portion of the area selected vms densely
covered with willow and birch shrubs to a height of 2 to 3 feet.
Figures 28 and 29 show typical parts of the open and shrub
covered areas. Drainage was towards the west, into the Churchill
River. There were scattered spruce and larch trees on the
higher ground, a small copse of these towards the northern

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85

end, and many rocks. Although somewhat scanty in the higher
area, the mosquito larval population here was considerably
higher than in experiment 1, and its extent was more clearly
circumscribed by the well defined pools. The most important
species were A. punctor, A. campestris , and A* flaveseens,
and these were present in second third and fourth instars. A
species of Chaoborus was also present in considerable numbers
at stations 2 and 5. There were many fish and frogs in the
pools; none of these were observed to suffer any direct harm as
a result of the insecticide.

Thirty dipping stations were marked out within this
area. These were selected with different degrees of exposure;
number 11, a typical station is shown in figure 30. The larval
population at each of these stations was estimated by dipping
with 600 cc. capacity dippers. Five dips were taken at each
station by each of two independent observers. When more than
12 larvae were obtained in a single dip, this was recorded as
T12 plusT. The pretreatment count at the first 19 stations was
taken on the ev-ning of June 19, and at the remaining 11 stations
mostly in the higher area, on the morning of June 20. The
detailed counts are shown in the first group in table 3; the
average number of larvae per dip was 3.14.

The insecticide was dispensed from 10.50 a.m. until
3.30 p.m. on June 21, using the same equipment and material as
in experiment 1, but during the second half of the run it was
found necessary to tow the generator once along the base line,
stopping for a calculated period at 25 yard intervals. This
change was made on account of the very rough nature of the ground

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figure 29: A general view of the shrub
covered area, experiment 2.

figure 30 : Station
dipping

11, a typical
station.

87

TABLE 3. Population estimates and percentage mortalities at
varying distances from the base line. Experiment 2,

- - or—

P

CO

Count

Count 24 hrs.

Count

48

~ 1

hrs.

Characteri sti cs

before

after

after

of pool

P

treatment

treatment

treatment

•H

.20. VI. 47

22. VI

.47

23.

VI.

47

<D

p

•H

Larvae .

i — i

!>-,

0

•H

-P

•H

00

(H

i — 1

Cd

cd

Ctf

,P

p

-P

P

0 E

£ O

p

U

o

B

B

B P

P Oh

0

©

a

bO

bC

0

cd

cd

P o

p

p

o p

©

P

0

P

•h cd

cd

0

0

cd

0

©

-p -p

K5

cd

O

►>

cd

o

cd to

P

P,

p

p

P.

P

P .H

cd

2

0

cd

2

0

ca o

p|

Ph

Ph

fP

P-.

1. 30

26

23

»

20

Open, grassy

2. 60

5o+

2

1

95 +

-

-

100

Open, grassy

3.100

27

-

-

100

-

6

85

Open, some shrubs

4.140

35

21

-

33

5

-

86

Slightly screened

5 . 220

49+

1

1

96 +

1

1

97 +

Slightly screened

6.230

40

2

-

94

5

-

87

Slightly screened

7.290

29

12

1

51

-

4

91

slightly screened

8.320

51

lo

4

62

-

6

92

Open, grassy

9.380

"17

7

4

40

2

2

81

Open, grassy

10.430

34

14

2

50

14

5

51

Slightly screened

11.470

59

20

-

62

9

-

85

Heavily screened

12.420

32

7

-

75

3

5

80

Slightly screened

13.400

62+

48

-

13+

10

-

84+

Slightly screened

14.300

23

1

-

95

„

-

100

Slightly screened

15 . 240

26

7

-

70

3

-

88

Heavily screened

16 . 190

23

3

-

85

3

-

87

Heavily screened

17 . 180

27

■ 13

45

9

-

67

Heavily screened

18 . 130

33

: 12

1

57

13

1

58

Heavily screened

19.100

20

! 2

2

83

»

-

100

Heavily screened

20.270

28

; 7 ■

-

72

8

-

71

1 Slightly screened

21.270

21

i 10

-

46

-

-

100

: Slightly screened

22.300

6

1. 3

-

43

1

1

72

| Heavily screened

23.580

23

! 14

-

30

2

8

68 .

| Open, grassy

24.530

51

7

38

43

6

24

57

I Open, grassy

25.540

32

22

-»

22

15

1

51

1 Heavily screened

26 . 550

27

6

4

67

4

3

78

Open

27 . 280

22

2

95

2

7

70

i slightly screened

28 . 250

16

3

4

65

T

7

71

Slightly screened

29.180

31

12

_

56

2

-

94

Heavily screened

30.180

18

2

1 - — .

-

87

1

-

94

Heavily screened

■ 1

88

and was found to be far more satisfactory, reducing wear and
tear on machines and personnel to a minimum, and virtually
eliminating end effects due to time taken in turning. A reduction
of the distance between stops to 10 yards would be preferable,
at least in experimental work, as the lateral spread is not very
great, when meteorological conditions are suitable for aerosol
application. The effect of an appreciable wind shift during
operation in this manner would, of course, be far more serious,
but such an eventuality did not arise. The greater time taken
to dispense the material in this experiment was partly due to the
greater amount of material, and partly to mechanical difficulties
with the generator. There were numerous stoppages; three on
account of choked filters, and one on account of engine trouble,
appeared to have been unavoidable with the equipment as used.

The longest continuous operation obtained was 25 minutes. These
difficulties may have been accentuated by the rather violent
movement of the vehicles.

The wind in the early morning was NW which would have
been very suitable for spraying from the north end of the plot.

By the time the equipment was assembled at site, ho?/ever, this
had changed to SW, and a new base line was set out at 45° to the
original line passing through the two 100 yard marks N and E
respectively of the SW corner of the original plot, and with its
centre mid way between these. The new plot included all the
dipping stations except no.l. which fell south of the centre of
the base line, and no. 10 which fell just outside the western
side line at about the 500 yard mark. The layout of the initial
and the ultimate plots, and of the dipping stations is shown
in figure 24.

89

The sky was overcast almost throughout the treatment;
the wind was blowing from a direction slightly west of that of
the plot during the first half of the treatment, but veered to
slightly east of this direction during the second half. There
was thus a tendency for the dosage on marginal dipping stations
to be low, and for that on the central stations to be high.

Wind speed recorded on the ridge by the airstrip was 10 m.p.h. ,
that at the site was considerably less and was estimated at
about 4 m.p.h. , strengthening somewhat later to about 6 m.p.h.

From the behaviour of the cloud which clung closely to the ground,
rather poor inversion conditions prevailed. Air temperature
rose from 58 to 65°F. during the treatment; humidity was moderate,
and barometric pressure rather low, and falling.

The generator was in operation over the plot for a
total time of 125 minutes, during which time 47 imperial gallons
of emulsion were dispensed; this figure corresponds to 18 lbs.
of DDT or 3.6 lbs. per hundred yards of base line. Assuming
that virtually all this material was deposited within the test
plot, this means an average deposition of 0.29 lbs. DDT per acre.

The cloud of insecticide could be seen clearly for
200 to 250 yards, and appeared to be settling down nicely; after
two runs a definite film ?<ras visible on pools at 100 yards, but
there were still quite a number of adult mosquitoes on the wing
in the cloud. Walking in the aerosol cloud down wind from the
generator, xylene could be smelled distinctly for a distance
of 150 yards; from 100 yards onwards, the odour of DDT became
noticeable as well, and this persisted up to a total distance
from the machine of at least 400 yards. Before the end of the

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MORTALITY PER CENT MORTALITY PER CENT

MORTALITY - GRAPHS

EXPERIMENT 1

X

20

Too 200 300 * 400 500

DISTANCE FROM BASE LINE IN YARDS

Figure 51

91

treatment, many adult insects, mainly mosquitoes and other
diptera (Tipulidae, Dolichopodidae , Scatomyzidae) , had been
knocked down on to the pool surfaces, and some mortality of
mosquito larvae could be detected.

The first population estimate after treatment was
made 24 hours later, on June 22. The weather conditions were
very much the same as during the treatment, but nearly 0.1 inches
of rain had fallen since the initial estimate. The dilution
resulting from this is reflected in the reduced population in
the untreated check station (no.l) , and in calculating apparent
percentage mortalities the counts at this estimate have accord¬
ingly been increased in this proportion, viz; 26/23. While
carrying out this estimate the smell of DDT was clearly noticeable
when walking through thick shrubs, presumably from a deposit
brushed off the leaves. Partial elutriation of this deposit
into the pools by rain may have influenced the results obtained.
Many dead sawflies, craneflies, midges and dolichopodid flies
were seen on the pool surfaces during this count.

As there were virtually no pupae in the majority of
pools at the initial estimate, pupal figures obtained in the
24 hour count were, on the assumption of a uniform pupation rate,
weighted as one half larvae in calculating mortalities. Detailed
figures are set out in the second group in table 3. The mean
percentage mortality for the whole area after 24 hours was not
less than 63 per cent.

A final population estimate was made 48 hours after the
"treatment, on June 23. The temperature was then much lower and
the humidity much higher than at the previous two estimates, but

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92

the barometer was rising rapidly, the wind speed had increased,
and there had been no appreciable rain since the 24 hour estimate.
The amount of water in the pools appeared to be approximately
the same as that found at the beginning of the experiment; this
is unfortunately not shown in the count on station 1, as this
had been upset by contamination with oil from a passing vehicle.
Larval counts in this estimate were accordingly taken at their
face value, while pupae were valued at 2/3 larvae. Detailed
figures are given in the third group in table 3, and a graphical
interpretation of these in figure 31. The mean percentage
mortality for the whole area after 48 hours was not less than
81 per cent.

Discussion: At the dosage used in this second experiment a

useful mortality was obtained over the whole of the plot observed.
It would have been of considerable experimental advantage, however,
to have extended entomological observations to a greater depth
from the base line, so that 50 per cent mortality at least were
included within the observed area. 1000 yards would have been
a more suitable figure. It appears from a consideration of the
graph (Fig. 31) that at this dosage, 50 per cent mortality could
be expected at a distance of about 700 yards from the emission
point, and that to obtain better than 90 per cent mortality over
an area of country under these conditions, it would be necessary
to traverse this at right angle to the wind direction at
intervals of about 500 yards.

Only one living specimen of Chaoborus sp. was taken
in the 24 hour count (station 5), and none at all in the 48 hour

93

estimate. This would suggest 100 per cent mortality for this
species at 220 yards, and consequently, that DDT is no less
toxic to these larvae than it is to the larvae of Aedes .

The low mortality figure for station 10 is attributable
to the fact that this station was outside the plot boundary.

The absence of any marked difference in mortality between the
open and the heavily screened dipping stations would seem to
indicate that in spite of the relatively large droplet size,
the material was showing true aerosol characteristics.

Weather conditions, as in the first trial were
remarkably favourable: there ?/ere only about six days during
this season- Y/hen both the mosquito larval population and the
meteorological conditions were suitable for this method of
dispersing insecticides. The most important adverse meteoro¬
logical factor is high wind speed. This coupled with the slowness
in action v/ould be the main obstacles to the successful operation
of this equipment here. A single machine in 1947, working 16 hour
days whenever conditions were suitable, would have treated only
a little over three square miles. With the existing mechanical
shortcomings, even this figure could not have been approached,
and in any event, the area would have to be selected for its
traversable nature. A generator of greater capacity as used by
Brescia and Wilson (11) or a battery of such generators, to
permit continuous movement at about 4 m.p.h. would be a necessary
development.

The results obtained in both experiments are not in
disagreement with those obtained in, or predictable from similar
work elsewhere (25,33,58), so that there would not appear to be

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94

any other special problems with regard to this method of
insecticide application at high latitudes. Rather the general
absence of very broken country would tend to favour the predict¬
able deposition of an aerosol.

There is some evidence that high wind difficulty is
partly a local effect only, resulting from sea breezes. Further
inland, at least south of the tree line, more moderate wind
speeds are to be expected, and in such areas, aerosol application
should prove easier. It is relevant to note that both the adult
mosquito and the aerosol, operate more satisfactorily at the
lower wind speeds.

5.1.2. A test of the Besseler Aerosol Generator
against Adult Mosquitoes:

An experiment was performed during the period July 1
to July 3, 1947, to test the usefulness of the Besseler aerosol
generator against adult mosquitoes in wooded country. Although
the experiment was not a successful one, in that no very real
test of the equipment resulted, nevertheless it proved of some
value in demonstrating some of the difficulties which would
face routine control measures equally with experimental work,
in employing this generator in country such as that around
Churchill .

Two provisional plots for this experiment were selected
on July 1. The first of these was in the vicinity of Farnworth
Lake, to the south of Churchill, and could be treated from a
vehicle on the Radio Range road, given a suitable southwest wind.
The second was a strip of wooded country running north and south

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95

about a half a mile beyond the eastern end of the east-west
runway of the Churchill aerodrome. The wind on the morning
of July 2 being from the south, it was decided to use the
second of these plots for a test the same evening. Meteorological
reports indicated that the wind might be expected to remain in
the south, and that the wind speed should moderate. Detailed
meteorological data were recorded.

The locality was visited during the afternoon, and a
400 yard base line was set out on a bearing of 100° from the
point 951074. This gave a plot depth of nearly 1500 yards, the
first 150 yards being open country, and the remainder woodland,
mostly rather stunted spruce. The general appearance of the
terrain is shown in figure 32. A wooded area some 500 yards west
of the test plot was selected as the control area, and an
alighting rate figure of 31 was obtained here, as compared with
33 for the wooded area of the test plot. Each, figure is the mean
of eight readings. All observers throughout the experiment wore
one of four standard and comparable mosquito repellents on the
face and hands.

At 6.00 p.m. the wind was reported to be moderating,
and from the same bearing, but the temperature had dropped
considerably. It was decided to run the test, although conditions
were far from ideal, truly ideal conditions being very rarely
obtained at Churchill. By the time the equipment had been assembled
the wind bearing had dropped 50° to 140u, the speed, though rather
high, was satisfactory, but the temperature had fallen to 56°F.
and rain threatened. To compensate for the wind shift, the base
line was reset to a bearing of 50° from the point 952075. This
change resulted in the first 400 yards only of the plot depth

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96

being in wooded country. At about 400 yards, a rocky cliff,
some 30 feet in height, led up on to flat, higher, rocky open
country, where the wind speed was considerably greater, extending
back to the shore of Hudson Bay,

Observers were stationed at 100 yard intervals from
the base line to a depth of 900 yards. Hach observer took five
readings, the individual readings at intervals of 25 yards
along the central 100 yard portion of the plot at the distance
at which the observer was stationed (Fig. 34). These five
observations were taken immediately before the discharge of the
aerosol commenced, and were repeated immediately after this was
completed. Nil readings were obtained both before and after
the release of the aerosol at all stations more than 400 yards
from the base line; i.e., at all stations on the open and
higher rocky area. Readings obtained at other stations are
recorded in table 4. The mosquito species involved were A.
nigripes , with some A. nea ret ions .

The Besseler generator was mounted in a tracked
amphibious trailer and towed by an amphibious weasel (Fig. 33).
The insecticidal material employed in the generator was a 10
per cent W/V solution of DDT in fuel oil with added Williams’

Red dye. The coil temperature employed was 300°F. , equivalent
to a mass mean droplet diameter of 20 microns and a discharge

rate of 35 imperial gallons per hour. The equipment was moved
along the base line, stopping at each 25 yards distance until
the expiry of a three minute period from the time of leaving the
previous stop. The total emission time was thus 48 minutes,
during which period 21.5 gallons of insecticide were used. Since

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Figure 32: A general view of the terrain
with amphibious weasel in the
foreground.

Figure 53: The Besseler generator in an
amphibious trailer.

LAYOUT OF PLOT

IOO YARD SQUARES

orig

Figure 34

TABLE 4. Mosquito alighting rates at various distances from
the base line at different times after treatment.

Distance from
base line in
yards

.

6 hrs.
before
treat-

s ment
!

.

Immedi ately
before
treatment

Immediately

after

treatment

24 hours
after
treatment

100

0,1,6,5,10

0 5 0 j 0,0,1

48,59

200

-

0,1,0, 1,1

0,0,1, 0,0

39,54

300

33

2, 3, 0,1,1

0,0, 0,0,0 .

- -

350

-

-

-

6,12

400

-

0,0, 2,0,1

0, 0,0,0, 0

41,45

Check site
(untreated)

31

-

-

35 , 37

Average

alighting

rate

32

1.75

L

0.1

37.6

All counts beyond 400 yards were nil.

* JHf. i u, ■, „ "t •j 'JO

■ • ' .; i . ( v . : i.; i ,

■

100

this was expended over an actual front of 375 yards, this gives
a figure of 5.73 gallons of solution, or 5.73 lbs. of DDT
per 100 yards of front. Assuming practically all of this
material to be deposited on the observed area, this would give
a mean figure of 0.31 lbs. DDT per acre.

The wind bearing during the emission period fluctuated
between 150 and 170°, with a speed between 14 and 20 m.p.h. in
the open, and 9-10 m.p.h. in the wooded area. No readings
were taken on top of the rocky flat. The barometer was
falling rapidly, and the air temperature dropped from 56 to 51°F.
during the experiment, the relative humidity rising from 81 to
94 per cent. The temperature gradient between one and two
metres ranged from 0 to 0.12°C, giving a parameter R (8) value
of 1.14 to 1.13. The sky was very heavily overcast almost
throughout the test, and there was some very light rain.

Emission started at 7.22 p.m. , and this, together
with the conclusion of the emission at 8.10 p.m., was signalled
to the observers in the plot by Yerey pistol. The aerosol was
emitted from all four nozzles of the generator, the cloud
drifting satisfactorily, though rather rapidly, into the woods.
The observer at the 100 yard point reported the cloud visible
after three minutes from the start of the emission, and the
observer at 200 yards after 15 minutes. No observer on top
of the rocky flat reported the cloud visible at any time, but
the smell of the aerosol was noticed independently by observers
at 800 yards and 900 yards, about 4 minutes after the start of
the emission. No mechanical difficulties were encountered with
the generator. This experiment clearly demonstrated the

101

disadvantage in experimental work of covering the area by

f

intermittent stops on s single run; wind shift during the
emission was such that from the last two or three stops at the
NE end of the line, none of the aerosol covered the plot at all.

A final survey of the adult mosquito population was
made at 5.0 p.m. on July 3, the figures obatined are recorded in
table 4. Mosquitoes were active throughout the area, including
the top of the rocky flat, and were very intent on feeding. The
barometric pressure had fallen still further, but the wind speed
was less and the humidity higher; other meteorological conditions
were unchanged from the time of treatment.

Discussion: It is not possible to say at all definitely how much

of the reduction in immediate biting rate during the experiment
was due to the action of the insecticide, and how much to adverse
meteorological conditions. The fact that later in the season
high alighting and biting rate figures were obtained with air
temperatures down to 50°F. and even below this, with strong
winds in addition, supports the view that the insecticide was
the main cause of the reduced alighting rates. Observations in
other experiments on plots up to one mile square sprayed from
the air (McDuffie et al, Goldsmith et al) and also general
observations on the habits of the species of mosquitoes involved
here, indicate that complete repopulation of a plot this size,
could readily occur within 24 hours.

On the other hand, although the figures indicate a
mean reduction in alighting rate of 94 per cent over the first
400 yards of the plot, the percentage mortality obtained in the
total population was probably very much less than this. David

102

and Bracey (17) have shown for droplets of 10 microns and less,
that impact on the insect is brought about by movements of the
insect rather than of the droplet. This probably remains in
large measure true for droplets of the size used in this exper¬
iment, so that mortality among the resting mosquitoes, which at
the time of treatment constituted a very large proportion of the
total population, would have been very small. These resting
mosquitoes were in fact probably very largely responsible for the
rapid build up of a large active population after the treatment.

The momentary and local smell of the aerosol which was
detected on top of the rocky flat may be taken to indicate either
that the high wind speed was inimical to uniform distribution,
or that the wind direction being normal to the rocky cliff
resulted in up currents being set up above this, which carried
the bulk of the aerosol well clear of ground level. Probably
a combination of these factors was operating.

The absence of mechanical difficulties, and the greater
discharge rate make the Besseler generator more satisfactory
equipment for use in this area than the model of the Hochberg-
Lamer generator employed in the earlier tests against mosquito
larvae. The discharge rate of the Besseler generator, however,
is still too low to permit the necessarily large area to be
treated during the very short time when meteorological conditions
may be expected to be suitable.

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5*1.3. An Evaluation of some Insecticides against
the immature stages of Blackflies:

Introductory:

Apart from work with miscible oils and pyre thrum
preparations (24,80,81) which gave consistently uneconomic
control, very little previous work has been done with insecticides
against immature blackflies. In 1945 Fairchild (19) and
Fairchild and Barreda (20) demonstrated that a number of species
of Simulium occurring in Gautemala could be effectively
controlled by the application of a DDT emulsion to give a
concentration of 0.1 parts of DDT per million parts of water
for a period of one hour, and that both a solution of DDT in a
turpentine-kerosene mixture, and a suspension of DDT in water
with a wetting agent were equally effective. Garnham and McMahon
(22) have reported the local eradication of S. neavei Roubaud in
Kenya colony in 1946, using the much higher concentrations of
2 to more than 5 parts of DDT per million parts of water for
exposure periods of 30 minutes. At these dosages mortality
among fish and other animals was considerable. Steward (55)
found that in the laboratory, 0*25 p.p.m. DDT for one hour
caused almost complete mortality of Simulium larvae, while
Gammexane gave similar results at 0.125 p.p.m.

For purposes of comparison of these various exposure
times and concentrations, it may be assumed that the time- conc¬
entration curve for any given mortality approximates to an
hyperbola over the small range considered (15), and hence that:

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Dosages in these experiments may then be expressed as products
of concentrations in parts per million and exposure time in

104

minutes as follows:

Fairchild and Barreda - DDT 6 p.p.m./mins.

Garnham and McMahon - DDT 60-more than 150 p.p.p./mins.

Steward - DDT 15 p.p.m./mins.

Gammexan© 7.5 p.p.m./mins.

It was decided to attempt to confirm these results
under the conditions at Churchill, to compare the effect obtain¬
able with some other insecticides, and finally to explore the
possibility of reducing the time of exposure required. In view
of the great number of streams which would have to be treated
for effective control in an area such as that around Churchill,
the ability to do this would be of very great advantage. In
addition it was hoped to obtain further data on possible toxic
effects on eggs and pupae.

The work may conveniently be reported in the form of
seventeen experiments grouped into three main categories; two
experiments involving aerial application of insecticides, fourteen
involving direct application of insecticides to streams, and one
experiment in which the pupal stage was treated with insecticides
in the laboratory. Accounts of these experiments numbered
serially throughout, from one to seventeen, are given below.

The first two experiments in the second group are reported in
somewhat greater detail than the remainder, since an attempt was
made in these to secure quant i^-^yQ estimates of populations
and mortalities; this was found to be impracticable, and
qualitative estimates only, were attempted thereafter. The
predominating species of blackfly in all experiments was

105

Simulium venus turn; where other species were important, these are
mentioned in the account of the experiment concerned.

The following insecticidal preparations were employed
in this work:

1 - trichloro -2,2- bis (p-chlorophenyl ) - ethane (DDT) :

5 and 10 per cent W/V solutions in fuel oil with
0.5 per cent Williams’ Red dye added, the latter with
Velsicol A.R.50 as auxiliary solvent.

25 per cent emulsion concentrate with 65 per cent
Xylene and 10 per cent Triton X-100.

50 per cent wettable powder (Deenate 50?/).

1, 2,5,4, 5,6 - hexachlorocyclohexane (Benzene hexachloride j :

An emulsion concentrate supplied by Canadian Industries
Limited, containing 5 per cent gamma isomer.

Chlorinated Camphene (Toxaphene, 5956) :

25 per cent emulsion concentrate with 65 per cent
xylene and 10 per cent Triton X-100.

Chlordane (1068) :

25 per cent emulsion concentrate with 65 per cent
xylene and 10 per cent Triton X-100.

10 per cent solution in Velsicol A.R.50 and fuel oil.

Pyre thrum - piperonyl butoxide (FPB) :

Dodge and Olcott’s Pyrenone emulsion concentrate
(T.143) containing lOmgms. pyrethrins and lOOmgms.
piperonyl butoxide per cc.

Aerial spraying Experiments: ( 1 )

Two streams infested with blackfly larvae flowed in
part through three plots marked out for aerial spraying trials
against mosquito larvae and adults. A blackfly survey of these
streams was made before the spraying to ascertain its effect on
the blackfly larvae. The first of the streams flored through
the first aerial spray plot only, for a distance of about 900
yards.

'The first half mile of the second stream was in the
second aerial spray plot, described under experiment 2, the

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second half mile in the third aerial spray plot, and only the
last half mile in the first aerial spray plot. Sight observation
stations were marked out in the first stream, and five in the
last half mile of the second; at each of these stations there
was a moderate to heavy population on the afternoon of June 27.

No pupae were present at this time. The mean depth of each
stream, and the rate of flow were estimated at the same time, the
latter by timing a surface float over a measured distance to
get the maximum speed, and calculating the total flow from the
formulae :

V* - 2/3. V (approximately)

m

and: Flow - V_.A

a.

where V is the measured maximum speed, Va the average speed, and
A the cross sectional area of the water channel. This method
was found to be sufficiently accurate for these small streams,
providing suitably uniform sections of the stream were selected
for measurement, and a sufficient number of timings taken.

Spraying was carried out on the evening of June 27,
the temperature of the water at this time was 58°F. Details of
the spraying procedure are given elsewhere (McDuffie et al); it
is sufficient to mention here that the material used was 5 per
cent solution of DDT in fuel oil, and that this was put down at
a mean concentration of 0.26 lbs. DDT per acre. The population
of blackfly larvae was re-checked on the afternoon of June 28,
and on July 21, and August 7. No living eggs, larvae, or pupae
of any species of blackfly were found anywhere in the treated
length of the first stream at any of these examinations.

Untreated portions of the stream, and similar untreated streams
in the same vicinity, continued to harbour immature stages until

107

at least August 7. In the treated length of the second stream,
the only larvae found at the examination on June 28 were at
station 5, where there were two or three half grown larvae per
plant, on grasses rooted in the centre of the stream. This
station was very near to the upstream limit of the treated length,
so that the exposure time was very short indeed, and the insect¬
icide probably not well distributed. At the later examinations,
which were made after the upper reaches of the stream had also
been treated, no living eggs, larvae or pupae were found.

The results of these observations, together with those
on all streams treated in 1947 are summarised in table 5, and
the locations of all treated streams, including those treated
in 1948, are shown on the map in figure 55. DDT concentration
in streams treated from the air was estimated on the assumption
that all the material falling on the surface of the stream was
carried along in it, as follows:

Concentration in parts per million =

0

Deposit in lbs, per acre x 10

4840 x 9 x Mean depth in feet x 62.5

In the range of exposure time given, the minimum time
represents the theoretical time for the water which received the
spray to flow past the highest upstream observation station; the
maximum time relates likewise to the furthest downstream station.
In stream 1 the highest station was about half way between the
limits of the sprayed length, so that here the minimum exposure
time was quite high.

Aerial spraying experiment ( 2 ) :

The second aerial spray plot covered half a mile of
stream no. 2 from the source downwards. This was checked over

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for blackfly larval population on the morning of June 30,
immediately before the spraying, when 4 stations, each with a
heavy to very heavy larval population were marked out. The
temperature of the stream water was 55°F. The same insecticidal
material was used in spraying this plot, but the deposit was
0.48 lbs. DDT per acre; details of the spraying are given else¬
where (McDuffie et al ) . The stream was re-examined on the same
afternoon about three hours after the end of the spraying, when
the water temperature was 63°F. Only a very few sick looking
larvae were found, less than 1 per cent of the previous population,
all of them near the origin of the stream in a poorly defined
area largely under water. Many of these were hanging on silk.

A further examination on the morning of July 1, water temperature
54°F. , disclosed no living larvae at all, either in the treated
stretch or below this. Subsequent examinations were made on the
same dates as for stream no.l, and with the same results.

Scum, consisting of insects, spray material, and debris,
which had accumulated on vegetation at the margins of the stream,
was collected in water on the afternoon of the spraying, and
preserved in alcohol for later examination. Detailed examination
was carried out at Edmonton from August 20, to 30, 1947, when
the condition of the material was found to be such that
identification of most insects beyond the family was not practicable
The groups of insects and other arthropods represented
in this material, with the number of specimens of each obtained
are as follows:

Other Arthropods:

Araneae 23

Acarina

Hydracaridae 13

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Figure 35: Map showing the location of Blackfly
breeding streams treated with
insecticides. Double circles, 1948
treatments. (No. 2, 1948 = no. 3 1947).

Insects:

Apterygota

Collembola

Arthropleona (3 spp.) 223

Symphypleona 448

Exopterygota
Plecoptera
Nemouridae

Nemoura spp. nymphs 37

adults 91

Thysanoptera

Ihripidae 8

Homoptera

Aphidae 1

Chermidae nymphs 5

adults 2

Goecidae

Steingelia sp.nov. 10

Endopterygota
Coleoptera

Carabidae 3

Elateridae 3

Dytiscidae larvae 2

adults 4

Ghrysomelidae 2

Hydroseaphiidae 6

Trichoptera

Limnophilidae 1

Dipt era
Nematocera

Culicidae Aedes spp. males 2

females 8
Chironomidae pupae 7

adults 1504

Heliidae 16

Simuliidae larvae 43

adults 3

Hycetophilidae 53

Cecidomyidae 9

Seatopsidae 5

Brachycera

Dolichopodidae 6

Empidae 13

Cyclorrhapha

Lonchopteridae 2

Cordyluridae 2

Syrphidae 1

Phoridae 8

Chloropidae 5

Anthomyidae 4

Hymenoptera
Ghalastogastra

Tenthredinidae 3

Cimbicidae 1

Ill

Clistogastra

Ichneumonidae

Mymaridae

Proetotrupidae

2

6

4

6

2

Chaleidae

Gynipida©

This represents a total of some 2600 specimens
belonging to 37 different families, of which only 56 specimens
(representing 2 families) belong to species it was desired to
control. Of the remainder, many are parasites and predators,
some of them, in the families which are to be controlled; others
are competitors with these. Although this was clearly not a
strictly random sample, it serves to indicate how insignificant
the objective result of such an operation may be in comparison
with its total effect on the biocoenotic equilibrium.

The third aerial spraying operation, on the morning
of July 3, put down a deposit of 0.26 lbs. DDT per acre on the
half mile stretch of stream no. 2, in between the portions
treated in the first and second operations. As this stretch had
been found to be without larvae two days previously, no further
entomological observations were made on it at this time. In
later surveys made on the other stretches of this stream, this
stretch was found to be equally free of infestation.

Direct Application of Insecticides to Streams :

It had been intended to conduct these experiments
primarily with emulsion formulations, as these appeared to be
the logical preparations for this purpose. In view of the
results obtained in the aerial spraying experiments with the
cheaper and more readily obtained oil solutions, however, it was
decided to concentrate on these, and to employ emulsions only

112

for the purpose of comparison.

The first step in the procedure adopted was the select¬
ion of a suitable stream for experimental treatment; the require¬
ments are a high population of blackfly larvae, a well defined
channel presenting a reasonable length without undue tributaries
or distributaries, and suitable localities for flow measurement
and insecticide application. Streams were surveyed in some
detail, the amount of material needed to give the required
concentration and time of exposure calculated approximately, and
this amount applied if possible at the same time. Usually an
observer would be present in the stream during the treatment, to
watch the progress of the insecticide down the stream, and
observe any immediate reactions of the blackfly larvae. In general
the insecticide was applied a short distance from the upstream
end of the surveyed length, in order to leave a portion of the
stream undisturbed for check observations. The stream was then
resurveyed as nearly as possible 24 hours after the treatment,
and in most experiments, again when opportunity offered after
another interval of about a week or more.

Fourteen streams were treated in all, using various
concentrations and exposure periods with each of the insecticides
listed in the introductory section. The results are summarised
in table 5. In special instances, samples of animal life
presumably killed by the treatment were collected on screens
fixed in the stream below the treated stretch. Water samples
were also taken from these streams for pH and salinity deter¬
minations. Detailed accounts of each stream treated follow:

Experiment 5: A substantial stream draining into Hudson Bay five

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miles east of Churchill camp, shown on maps as Eastern Creek.

It is a permanent stream, draining from an extensive area of
lakes some three miles inland, and has a well defined bed of
gravel and boulders. Throughout its length it flows through
open tundra meadow, but there are patches of birch and willow
near the mouth. The point selected for the application of
insecticide was at the junction of two small tributaries from the
west side, about a mile and a half stream length from the shore.
The p re- treatment survey of this stream was made on July 10.

Flow measurements were made at either end of the surveyed stretch
as a check on the accuracy of the method, and good agreement
between readings was obtained. The water was somewhat alkaline,
with a pH of 8.46, the salinity much lower than that in other
streams sampled, at 56 p.p.m. chlorides, measured as sodium
chloride. Six observation stations were marked out as follows:

1. 80 yards downstream from treatment point. Fine gravel
bottom; deeper; slower current. Patches of larvae in lines
at about 8 to the linear inch on stones.

2. 380 yards downstream. Coarse gravel bottom; dimensions
and flow similar to treatment point. Very heavy larval
population on stones at the bottom and on vegetation at
stream margins.

3. 630 yards downstream. Island at eastern bank. Medium
gravel bottom. 10 to 20 one-third grown larvae per linear
inch on grasses.

4. 880 yards downstream. Mixed clay and gravel bottom;
stream breaks up round several islands. Very heavy
population, all stages from newly hatched larvae to pupae.

5. 1020 yards downstream. Boulders and very coarse gravel.
Moderate population of half grown larvae on vegetation on
the east side. Patchy heavy population on stones in centre

6. 1410 yards downstream. Rapids; many very large boulders
Patches of larvae on vegetation at sides and rocks in
centre. One-third to two-thirds grown.

Three species of Eusimulium, probably new species
were present here in addition to S. venus turn. Two 3 foot by 4
foot sampling screens with 16 meshes to the inch were fixed in

114

the stream, ten yards below station 6.

Treatment was with 10 per cent DDT in oil solution
by means of a gravity dispenser contrived by C.N.Husman. This
consisted of a 4 gallon drum fitted with a wheel valve laterally
near the bottom, leading through five feet of 3/8" bore rubber
tubing to a four foot length of 5/8" bore copper pipe, and
was calibrated for discharge rate at various valve settings
beforehand. This was arranged with the container on the bank
of the stream, and the outlet of the copper pipe held in a
wooden support 2 - 3" above the water surface. Treatment was
done on the afternoon of July 11, and the oil spread, mixed in,
and carried well, although a strong SE breeze resulted in some
piling up of insecticide in bays on the west bank. The concen¬
tration was one part DDT in ten million parts of water for an
application time of 50 minutes. After 25 minutes treatment,
larvae were beginning to release from the vegetation about 50
yards downstream. Good turbulence immediately below the ’site
of application was a primary factor in the good distribution
obtained.

The stream was examined again 24 hours after the treat¬
ment; no attached or living larvae were found at any of the
observation points or elsewhere in the treated stretch. Specimens
of pupae were collected from the treated and untreated portions
of the stream for rearing. The screens from the downstream end
were collected and the material from them preserved in conjunction
with that from experiment 4 for later examination. 58 per cent
emergence was obtained from pupae from the treated portion, so
that there was no definite evidence of toxicity to pupae. A final
examination of the stream was made on July 24, 15 days after the

115

treatment, by which time some reinfestation had taken place.

No pupae were found, but there was a very general light
infestation composed of all stages up to two-third grown
larvae, with a preponderance of very young larvae. Unlike the
streams draining into the Churchill River, there had been no
great reduction in flow.

Experiment 4: This was done in a smaller stream than the last,

draining from a small lake into Hudson Bay about 2~k miles east

of Churchill camp. There was more variation in the character of

this stream, which ran in some places between high banks, and

had some stretches of clay, and some of sandy bottom. There was

rather more vegetation along the banks than at Eastern Creek, the

pH of the water was similar at 8.55, but the salinity was much

higher at 143 p.p.m. Surveys and treatment were made on the

same days as for experiment 3, the following 5 observation

stations being marked out over a length of half a mile:

l.S-bend, 160 yards below point of treatment: many pupae on
vegetation and a few half grown larvae on stones. Coarse
gravel bottom.

2. 260 yards downstream. Island in centre of stream. Some
pupae on stones very few larvae. Boulders.

3. 560 yards downstream. Group of grassy islands in centre,
fine gravel and sandy bottom. Few larvae and pupae on
vegetation.

4. 610 yards downstream. Rapids below small bay. Medium
gravelly bottom. Many larvae on stones.

5. 820 yards downstream. Small rapids; medium gravel with
boulders. Yery few half grown larvae on vegetation, none
on stones.

The larval population in this stream had decreased
greatly from that observed on previous visits on June 25 and
July 7. Two new species of Eu si mu Hum were taken here. Flow
measurements were taken at either end of the treated stretch,
and a sampling screen was fixed 20 yards below station 5.

116

The same 10 per cent DDT in oil solution was used
for treating this stream, but it was applied with an ordinary
hand spray pump. Dosage and application time were the. same at
0.1 p.p.m. for 30 minutes.

During the first half of the treatment the material was
sprayed onto the surface of the stream, with the jet held a few
inches above the surface. It was found that some of the finer
mist was carried away by the high wind, so that the procedure
was changed to spraying with the jet held under water. This
method seemed to be entirely satisfactory.

No attached or living larvae were found on examination
24 hours after the treatment. Pupae and eggs from the treated
and untreated parts of the stream, and material from the gauze
screens were collected. Adult emergence from the untreated
pupal material was 71 per cent, and from the treated material
47 per cent, giving a possible treatment mortality of 34 per
cent. Eggs from the treated and untreated portions of the stream
hatched uniformly with no detectable differences. The stream
was examined again on July 25, when in spite of a greatly
reduced flow, it was found to be liberally reinfested with all
stages from egg to pupa. A final examination on August 11 shov/ed
the stream very swollen by recent rain, with only a few larvae,
very few pupae, all within the upper 100 yards, and no eggs.

The material collected from the screens in experiments
3 and 4 was examined as follows :

The quantity of vegetable and inorganic debris mixed
in with the specimens was such that it was necessary to remove
all the larger fragments by hand for separate examination, and
then to elutriate off the smaller particles, also for separate

117

examination. The quantity of material obtained was so great
that complete counts were not practicable; a sample was taken
by dispersing the specimens in alcohol in petri dishes, and
making random complete counts on a number of fields of view
under a binocular microscope. These counts were then added, and
the material as a whole was scrutinized for the occurrence of
organisms which did not show up in the sample counts. The results
obtained by this method were as follows:

Totals in sample counts:

CRUSTACEA

Branch i op oda
Anostraca

Branchinecta spp. 11

Cladocera

* Eurycercus (glacialis?) 9

Daphnia spp. 15

Conchostraca

Limnetis spp. 75

Copepoda

* Heteroeope septentrionalis 9
Malaeostraca

Amphipoda

Gamma r us spp. 3

ARACHNIDA

Araneae 1

Hydracaridae 2

INSEC TA

Exopterygota

Plecoptera

Nemouridae

Nemoura spp. nymphs 31

adults 7

Ephemerida nymphs 10

Homoptera

Chermidae 2

Endopterygota
Coleoptera

Dytiscidae larvae 4

adults 3

Tri chop t era larvae
Hydropsychidae )

Ryacophilidae ) 10

Other families 16

118

Dipt era

Nematocera

Chironomidae larvae 11

pupae 9

adults 35

Simuliidae larvae 903

pupae 4

adults 35

Mycetophilidae 3

Brachycera

Empidae 2

(* It is reported that only one previous record of
each of these species exists.)

Representatives of the following groups were also
encountered in the general scrutiny: Collembola, Trichoptera
adults, Elateridae, Tenthredinidae, Tipulidae, Anthomyidae ,
and Mollusca - Pulmonata. With the possible exception of the
beetles the material was not in good condition, and closer
identifications could not be made.

Experiment 5: An appreciable proportion of the blackflies at
Churchill breed in artificial drainage ditches of the type used
in this and some of the succeeding trials. The turbulence in
these channels is at all times rather less than in the streams,
and late in the season is virtually absent. This channel was
flowing very slowly indeed, but had a very heavy larval and
pupal population for a surveyed length of 350 yards, the
population decreasing thereafter. This length included a right
angle bend under a railway culvert which provided ideal conditions
for flow measurement, at a distance of 200 yards from the point
of treatment. A sampling screen was fitted a further 200 yards
downstream. This, and the streams in experiments 6 to 9 were all
treated with insecticide on July 14. Treatment was again with
10 per cent DDT in fuel oil, applied to give a concentration of

119

TARIiE Summary of Data from Insecticidal Treatment of Streams

Exp.

Date

Observed Treated

Average

Insecticide

Method of

Concen¬

Application

Dosage

L A R V

AL POPULATION

No.

of

Treatment

Length of Stream
(Yards)

Flow in
Cusecs

Formulation

Application

tration

p.p.m.

Time

(Minutes)

(p.p.m. /min. )

Before

Treatment

24 Hours Al ter
Treatment

Subsequently

1.

June 27

900

12.20

5% DDT in
fuel oil

Aerial spray

0.095

15 to 30

1.425 to 2.85

Heavy

Nil

Nil for at least

41 days

2.

June 30

2500

10.00

5% DDT in
fuel oil

Aerial spray

0.150

0 to 60

0 to 9.00

Heavy

Nil

Nil for at least

41 days

3.

July 11

1400

88.00

10% DDT in
fuel oil

Gravity dis¬
penser

0.100

30

3.00

Heavy all
stages

Nil

Re infested with
young larvae in

14 days

4.

July 11

850

6.70

10? DDT in
fuel oil

Hand sprayer

0.100

30

3.00

Moderate

Nil

Reinfested with
all stages in 14

5.

July 14

250

0.57

10% DDT in
fuel oil

Medicine

dropper

0.590

15

8.85

Heavy and
mature

Nil after
first 100
yd.

6.

July 14

85

1.98

Fuel oil

Medicine

dropper

1.680

15

25.20

Heavy all
stages

Almost un¬
changed

—

7.

July 14

300

6.30

10% chlor-
dane in
fuel oil

Medicine

dropper

0.079

15

1.185

Heavy all
stages

Some con¬
trol for

100 yd.

Remained infested

8.

July 14

600

120.00

50% DDT
nettable
ponder

Portable

press.

sprayer

0.075

20

1.50

Very

heavy

Few first

350 yd. ,
nil beyond

9.

July 14

400

1.97

10% DDT in
fuel oil

Medicine

dropper

0.126

5

0.63

Heavy all
stages

Slight re¬
duction

Remained infested

10.

July 15

4400

270.00

10% DDT in
fuel oil

2 pressure
sprayers

0.176

15

2.64

Very

heavy

Nil after
first 100
yd.

11.

July 18

250

0.57

25% DDT
emulsion

Medicine

dropper

0.490

15

7.35

Heavy

One living
larva found

12.

July 20

80

0.87

5% gamma-
BHC emul¬
sion

Graduate

paddle

0.100

15

1.50

Very

heavy and
mature

About 50%
reduction

Remained infested

13.

July 21

650

0.54

P.P.B.U^-
renone )
emulsion

T. 143

Graduate

and

paddle

0.500

15

7.50

Moderate

and

mature

Reduced for

150 yd.

Remained infested

14.

July 21

1500

1.62

25% DDT
emulsion

Graduate

and

paddle

0.100

15

1.50

Moderate

all

stages

Nil

Nil for at least

10 days

15.

July 24

20

120

8.20

17.50

5% gamma-
BHC emul-

Graduate

And

paddle

0.190

0.089

15

2.85

1.335

Heavy

Heavy

Fen living
About half

Remained infested
Remained infested

16.

July 24

100

13.60

25% chlor¬
inated
camphene
emulsion

Graduate

0.164

15

2.46

Very

heavy

No change

Remained infested

* See explanation in Introduction .

120

about one part DDT in two million parts of water for a period of
15 minutes only. As the dosage required for this was only three
ounces, this was applied by medicine dropper, and timed by
stop watch. Pupae were collected from various situations in
the stream before and after the treatment. The oil spread well,
and moved slowly through the first part of the stream, more
rapidly, and with better mixing further downstream.

A preliminary examination at six hours after treatment,
and the regular 24 hour examination both indicated that the kill
of larvae was incomplete for the first hundred yards below the
point of treatment, but complete thereafter throughout the
surveyed length. Adult emergences were 21 per cent from the
untreated pupae, and 48 per cent from the treated pupae, so that
there was no evidence of pupal mortality due to the treatment.

The screen was removed at the 24 hour survey, and the material
collected from it was examined collectively vdth that from screens
out of other drainage channels, the results are given under
experiment 9.

Experiment 6; This was done in a drainage channel very similar
to the previous one, and with a very similar blackfly population,
but for a distance of less than 100 yards only. There was a
very heavy growth of shrubs along the banks, and the flow was
rather greater than in no. 5.

‘The treatment of this channel was with fuel oil alone,
for purposes of comparison with the results with insecticide
solutions in fuel oil. This was applied by medicine dropper
immediately after the survey was made, to give a concentration
of one part of fuel oil to about 600,000 parts of water, for a

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period of 15 minutes. - The behaviour of the material in the
channel was similar to that of the insecticide in the previous
trial. Pupae were collected before and after the treatment.

A very slight and local release of larvae occurred
just below the point of application, during the actual treatment;
the situation after 24 hours was unchanged from this. Pupal
emergence from the untreated sample was 51 per cent, and from
the treated sample 54 per cent.

Experiment 7: This was done in a small tributary stream, flowing
from Warkworth Creek into Goose River. There was great variation
in width, the stream flowing through a small pool, and fanning
out into a number of separate beds at its efflux into Goose
River. The bed consisted of gravel, stones, and boulders, and
the banks were rather open and grassy, but 'with spruce, larch,
and dwarf willow growing a little back from them. There was a
brisk flow, which was conveniently measured at the railway
culvert, from which the insecticide was applied.

For about 100 yards downstream from the culvert, the
blackfly larval and pupal population was heavy, though somewhat
localized; beyond this the population was sparser.

This stream was treated by medicine dropper with
10 per cent solution of Chlordane in fuel oil. The concentration
used was about one part Chlordane in ten million parts of water
for an application time of 15 minutes. Samples of pupae were
collected before treatment and 24 hours after this. Good
turbulence at the railway culvert aided distribution of the
insecticide, which seemed to pass satisfactorily through the
pool, and could be seen in the stream on the other side of this.

122

Figure 36: Goose River, treated in
experiment 8, 1947.

Figure. 37: Herriot Greek, treated in 1948

123

Some larvae could be seen to be releasing their hold on
vegetation at the conclusion of the treatment for a distance of
50 yards below the culvert. The stream was resurveyed 24 hours
after treatment, when there was a noticeable reduction in the
larval population near the point of treatment, although this
did not extend very far, and even above the pool it was no
longer perceptible. Percentage figures for pupal emergences
were not obtained from this stream, but a high proportion of
emergences was obtained from both treated and untreated batches.

Experiment 8: This involved the treatment of Goose River itself
(Fig. 36) at a point a little below the bridge on which the
Churchill Railway crosses it. This is a substantial river, with
a flow at the time of treatment of some 120 cusecs; unfortunately
it was not possible to survey this to any great distance below
the point of treatment, partly on account of inaccessibility,
and partly because it breaks up into a maze of secondary streams,
some of which were, however, encountered in the survey after
experiment 10. There are small rapids immediately below the
treatment point, and throughout the observed distance, the
bottom is of large stones and boulders, with patches of moderate
growth of filamentous algae and some higher plants.

Stones and vegetation bore a heavy population of
larvae, mostly nearing maturity, together with many pupae and
some eggs. Samples of pupae were taken from just below the
application point, and from 600 yards downstream.

Treatment was with a 'water suspension of a 50 per cent
DDT wettable powder, applied by a Dobbins portable pressure
sprayer, the operator wading bank and forth in tne stream.

124

The concentration used was about one part DDT in thirteen
million parts of water, applied for 20 minutes. During this
time there was an interval of 5 minutes for pumping up the
sprayer. The insecticide was applied on the morning of July 14,
the operator making four double crossings of the river.

The 24 hour survey of this river revealed a very
considerable reduction in the larval population, only a few
scattered living larvae were found, from the line of application
to a distance of 350 yards downstream. Beyond this distance,
pupae only were found to a total distance of at least 500 yards.
Substantial emergence of adults was obtained from both treated
and untreated pupae.

Experiment 9: This ’was done in a drainage channel, similar
to those used in experiments 5 and 6, with very little flow,
and practically no turbulence. Flow estimates were made at
the railway culvert, where the insecticide was applied also.

There was a heavy population of all stages of larvae
and of pupae for a surveyed distance of 400 yards below the
treatment point. Simulium venus turn was the dominant species
here, but Eu simulium iatipes was also present. A sampling
screen was used here.

A still further reduced dosage was applied here in
an attempt to discover what the marginal dosage would be.
Three-quarters of an ounce of 10 per cent DDT solution was
applied over a period of five minutes, giving a concen oration
of about one part DDT in eight million parts of water.

On resurveying after 24 hours there- was found to be
only a slight reduction in the numbers of larvae near the

125

point of application. The reduction increased further downstream

to a maximum of about 50 per cent from 75 yards onwards* Most
of the treated pupae which were taken from this stream gave
rise to adults.

The material collected from the sampling screen in
this experiment was examined collectively with that from
experiments 5 and 6. The procedure adopted in examining this
material was the same as that described under experiment 4,
except that the number of animal specimens obtained was so small
that there was no difficulty in removing and counting every
specimen. This was probably partly because of the much slower
current and the greater proportion of vegetable matter suspended
in the water, screens becoming choked with this material, and
hence inoperative, before many specimens had been caught* The
much smaller variety of species obtained is interesting:

CRUSTACEA

Malacostraca

Gammarus sp. 1

Concho strac a

Limnetis spp. 3

2

INSECTA

Exopterygota

Plecoptera 1

Bphemerida nymphs 17

adults 5

Endopterygota

Trichoptera larvae 1

adults 2

Dip ter a
Nematocera

Chironomidae larvae 3

pupae 2

adults 2

Simuliidae larvae 10

pupae 6

adults 3

Tipulidae 1

Br achy c era

Empi dae 3

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MOLLUSCA

Gastropoda

Pulmonata 8

Experiment 10: This experiment was carried out on Warkworth
Greek, which, with a flow of about 270 cusecs, was the largest
river treated. Flow measurements and treatment were both made
from the only convenient location, the Churchill Railway bridge.
In view of the size of the river, a somewhat more accurate
method was employed for measuring flow, applying Simpson* s
Rule, and using the bridge piers as ordinates. The bottom of
Warkworth Creek is covered with large boulders, and there is
moderate vegetation. The Creek breaks up into a number of
streams, unites with Goose River, flows through a fair sized
lake, and again breaks up into streams, before finally emptying
into the Churchill River some five miles below the bridge
from which it was treated.

A full survey of the population of blackflies was
not made before the treatment; some two hundred yards of the
river, above and below the bridge ,had been under observation
for some days. There was an abundant population of pupae and
larvae, the latter mostly between maturity and half growth,
on rocks and vegetation wherever the flow/ was adequate.

The flow/ estimate w/as made and treatment was carried
out between eight and nine o'clock on the evening of July 15.

2§ imperial gallons of a 10 per cent DDT solution were applied
over a period of 15 minutes. Application was made by two
operators with portable pressure sprayers, walking back and forth
along the railway bridge, and directing the spray down at the
water surface. Each operator worked from one half of the bridge.

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There was a slight loss of material, carried by wind, and
deposited on the bridge structure. The calculated concentration
was about one part DDT in six million parts of water.

24 hours after treatment a few larvae were still found
on rocks to a distance of about 100 yards from the bridge.

Beyond this, the main channels of the river were examined
thoroughly to a distance of 2£- miles. For part of this distance
the water is mixed with that from Goose River (experiment 8).

No larvae of any description were found beyond 100 yards from
the bridge. Pupae were collected from 1^ and 2 miles downstream,
and gave adult emergences of 55 and 80 per cent respectively.

Many fish, including suckers up to 18 11 in length were seen, a
good catch of jackfish was made at the bridge by a fishing
expedition two days later, and no complaints of dead fish or
reduced yield were made by the trapper who keeps his dogs on
the fish from fish traps about 200 yards upstream from the bridge.

Experiment 11: This experiment involved a second treatment on
the drainage channel which was treated, but not disinfested, on
July 14 (experiment 9) . There was a heavy population before the
treatment, consisting mainly of larvae.

Treatment was with a 25 per cent DDT emulsion
concentrate, applied by medicine dropper to give a concentration
of about one part DDT in two million parts of water for a period
of 15 minutes. Treatment was done at nine o’ clock on the morning
of July 18; examination at five o’clock on the evening of July
19 disclosed a single living larva below the treatment site, a
heavy population remaining above.

128

Experiment 12: The stream used in this experiment drains from
the Isabelle Lake system in a southwesterly direction, and is
controlled by a sluice gate and weir. The bed of the stream
is well defined for a length of about 80 yards only, thereafter
the water fans out into a grassy marsh. The stream was shallow
at the time of treatment, with a coarse gravel bottom, the
margins and the bed itself becoming more grassy proceeding
downstream. Earlier in the season, this stream harboured as
large a population of blackfly larvae as was to be found
anywhere close to the camp, but this population was well past
its peak at the time of treatment. Flow was measured at the
sluice gate. Pupae for rearing were taken before and after
treatment, and the pupae used in experiment 17 were collected
later, from the top of this stream.

A benzene hexachloride emulsion concentrate containing
5 per cent gamma isomer was applied at a point 20 yards below
the sluice gate on the afternoon of July 20. The emulsion was
diluted to four times its volume with stream water, and was
applied by dribbling it in from a graduate at the rate half and
ounce per minute for 15 minutes. The calculated concentration
was one part gamma BHC in ten million parts of water. In view
of the small length of stream available for observations, the
insecticide was mixed in just below the point of application
with a paddle.

Towards the end of the treatment larvae could be

seen beginning to let go, and a few minutes later, large numbers
of them were trailing on silks from their points of attachment.
Examination after 24 hours, however, revealed at least 50 per

129

cent of the larvae of all ages still present, alive and active;
water temperature was 62°F. The percentage adult emergences
from the treated and untreated pupal samples were 12 and 82
per cent respecti vely , so that there is evidence of considerable
pupal mortality due to this treatment. Further examinations of
this stream on July 28 and August 6, showed that the population
developed normally.

Experiment 13: This stream was not treated until July 21, by
which time lack of rain had left but little water in most of the
streams, and correspondingly small blackfly populations. This
stream flows through the area of heavy birch and willow shrub
growth adjoining the tidal flats on the east bank of the
Churchill River. A point of junction with a second stream was
selected as suitable for the application of insecticide, and 650
yards length of the stream below this point was surveyed. The
bottom was largely mud with scattered stones; the banks with a
very heavy growth of shrubs. Flow was measured in each of the
tributaries separately and added, the main stream offering no
length suitable for measurements.

The larval population was evaluated on the basis of
observations at 20 stations; at most of these there was a moderate
to heavy population of rather mature larvae.

Pyrenone emulsion concentrate was applied by dribbling
in from a graduate to give a concentration of one part piperonyl
butoxide to two million parts of water for a period of fifteen
minutes. This was mixed in v/ith a paddle. The temperature of
the stream water at the time of treatment was 61°F.

During the treatment, observations were made on larvae

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130

at a point 50 yards below tlie application site, where the
presence of the insecticide in the water could just be detected.
Six minutes after the first arrival of treated water, larvae
started to double up repeatedly, and the first larvae released
after a further four minutes. By the end of the treatment the
great majority of the larvae had released. At the resurvey 24
hours later however, there was found to be considerable infestat¬
ion remaining in the stream. Only at the first three stations
was there anything approaching effective control, the maximum
reduction in larval population further downstream being less
than 50 per cent. Specimens of treated and untreated pupae
gave 46 and 50 per cent adult emergences respectively.

Experiment 14: This stream runs parallel to that treated in the
previous experiment, and is very similar to it in character
except that the upstream portion of it consists of a straight
drainage channel, which provided very suitable conditions for
measurements of flow. Vegetation on the banks was somewhat
lighter, the bottom had more gravel and sand, the water was
clearer, and the blackflv population rather heavier. Observations
were made at 16 stations distributed over a length of 1500 yards.

A 25 per cent DDT emulsion concentrate was applied
for fifteen minutes on the morning of July 21 to give a
concentration of one part DDT to ten million parts of water.
Application was by dribbling in from a graduate, and mixing
with a paddle. The temperature of the water was 62°F.

The larval population at a point 50 yards below the
treatment site wan observed during the treatment, but the only
reaction was the release of a very small proportion of the larvae

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towards theend of the application. At the 24 hour examination
no blackfly larvae, living or dead, could be found anywhere in
the treated part of the stream; water temperature at this time
had fallen to 55°F. Many other insect larvae, especially those
of chironoraids and ephemerids, were seen living and apparently
unaffected by the treatment. Treated and untreated pupal
blackfly samples gave emergences of 60 and 64 per cent
respectively. A final examination on July 31 showed the treated
stretch still without larvae or pupae, these two stages being
present in about equal numbers in the untreated length of the
stream.

Experiment 15: This experiment, and the succeeding one, were
done in a portion of Eastern Creek upstream from that utilized
in experiment 3. The conditions of terrain and stream bottom
were similar to those in experiment 3, but as these streams
were tributaries which unite to form the main stream of Eastern
Creek, width and flow were less, although the depth was about
the same. In this experiment, a single application was used for
observations on the effect of two different concentrations by
treating a short distance above the influx of a tributary, flow
rates being measured both for the main stream and for the
tributary.

Infestation before treatment was heavy, and consisted
almost entirely of larvae on stones. Vegetation was very scanty,
and although empty pupal cases were quite numerous, no living
pupae were found.

Treatment was with 5 per cent gamma, BHC emulsion
concentrate, to give concentrations of one part in five million

132

and one part in ten million, above and below the tributary
influx respectively. Application was by dribbling from a
graduate and mixing in with a paddle, the application period
being 15 minutes. The temperature of the stream water was
63°F.

The treated stretch was resurveyed on the afternoon
of the following day. In the 20 yard length above the junction
(i.e. at the higher dosage), a few living larvae remained
attached to the rocks. Below the junction, the reduction in
population was less than 50 per cent.

Experiment 16: This stream was another of the upper tributaries
of Eastern Creek, similar in character to that used in the previous
experiment. The larval population was rather heavier, but again
no living pupae were found. A hundred yard length of the
tributary wassurveyed, and a situation with good turbulence
was found for the application of the insecticide. The material
used for treatment was a 25 per cent Toxaphene emulsion
concentrate; this was diluted with stream water, and applied
by dribbling in from a graduate to give a concentration of about
one part in six million over a period of 15 minutes. This
application imparted a distinct milkiness to the stream water,
but no release of larvae during the application could be seen
to occur. Treatment was done on the morning of July 24, and the
stream was re-examined on the afternoon of July 25. No change
in the larval population could then be detected.

Laboratory Experiments with pupal Blackflies :

Experiments were performed in the laboratory to
investigate the effects of the five toxicants employed in tne

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133

stream treatments on the pupal stage of s. venus turn. An attempt
was also made to obtain some information on the time-concentration
relationship for a fixed blackfly pupal mortality, with a given
toxicant of proved practical value.

erlmen t_17 : A large batch of pupae in cocoons attached to
grasses was collected from the stream used in experiment 12 at
2. J p.m. on July 18, and water for the preparation of insecticide
dispersions was collected at the same time and place. The
temperature of the water was 60°F . , pH was 8.4 and salinity 130
p.p.m.

Dispersions of the insecticides were prepared in the
following concentrations, expressed as parts per million.

Gamma BHC: 0.02, 0.04, 0.08, 0.16, 0.32, 0.64, 1.28 and 2.56;

DDT, chlorinated camphene, and Chlordane: 0.1, 0.2, 0.4, 0.8,

1.6, 3.2, 6.4, and 12.'8; pyrethrum-piperonyl butoxide (P.P.B. ),
based on piperonyl butoxide content: 0.5, 1.0, 2.0, 4.0, 8.0,

16.0, 32.0, and 64.0. One check container of plain stream water
was used for each batch of dispersions.

Batches of twenty pupae retained in their cocoons on
vegetation were then immersed, each for one minute, one batch
in each of trie above dispersions, including the check containers
of plain water. The batches immersed in the insecticides were
rinsed briefly in water from the same stream before setting them
aside for emergence in covered jars containing a little moist
cotton wool. During immersion the specimens were kept moving
slowly through the liquid to simulate the effects of stream
flow. 'The treatments were commenced at 4.0 p.m. on July 18 with
0.02 p.p.m. gamma- BHC, and continued with increasing concentrations

134

of this material, followed in sequence by DDT, chlorinated
camphene, P.P.B., and Chlordane, each in increasing concen¬
tration. Treatment was completed at 8.10 on the same evening.
During the treatment, most of the larvae present on the vegetation
were washed off into the treating fluid and were allowed to remain
there, at least ten larvae of varying size in each vessel.
Observations at 9.0 a. id. on the next day showed some of the
larvae to be still living in the following containers:

All containers of plain stream water.

Gamma-BHC: 0.02, and 0.04 p.p.m.

DDT: 0.1, 0.2, and 0.4, p.p.m.

Chlorinated camphene: 0.1, 0.2, and 0.4 p.p.m.

P.P.B.: none.

Chlordane: 0.1, 0.2, 0.4, 0.8, and 6.4 p.p.m.

Records of adult emergence were made on July 19 and 22,
and a final count was made on July 23. In a few batches a

conspicuous fungus growth developed and emergence was much
less than anticipated, but apart from this there was good
correlation between concentration and mortality, and emergence
in the controls was very uniform. The results obtained are set
out in table 6, and the graphical expression of these results in
figure 38 indicates L.D. 50*3 for gamraa-BHC and chlorinated
camphene of 0.15 and 1.9 p.p.m. /minutes respectively. The
mortality given by DDT, P.P.B., and Chlordane was too erratic
for reliable interpretation, and was not sufficient at any
concentration to compare favourably with that given by the above
two materials.

These results indicate the desirability of investi¬
gating the relationship between exposure time and concentration
for a given mortality for gamma-BHC. Attempts to do this were
unsuccessful on account of a dwindling pupal population.

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135

TABLE 6. The number of adult blackflies emerging from 20 pupae
after one minute immersion in various toxicant
di spersions .

Concentration
in parts per
million

0.0

(check)

0.5

1.0

2.0

4.0

8.0

16.0

32.0

64.0

P.P.B.

16

5*

12

15

12

11

5

3

2

Concentration
in parts per
million

0.0

(check)

0.1

0.2

0.4

0.8

1.6

3.2

6.4

12.8

DDT

5*

10

13

13

14

14

10

13

10

Chlorinated

camphene

16

15

!

14

14

9

8

7

6

4

Chlordane

15

8*

9

15

10

5

8

6

11

Concentration
in parts per
million

0.0

(check)

0.02

0.04

0.08

0.16

0.32

0.64

1.28

2.56

Gamma-BHC

17

13

13

14

12

5

3

1

0

* Results upset by fungous growth on pupae

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in 3 o aid Ainviaow

PARTS PER MILLION

137

Discussion: There has been some controversy as to whether
DDT and other insecticides actually kill the blackfly larvae
in treated streams, or whether they merely cause them to release
their hold, possibly to reattach further downstream, where the
concentration may be reduced by the junction of tributaries
and the influx of drainage water. In the Churchill locality,
the opportunities for re-attachment are slight, and may only
present themselves to larvae in streams draining into the
Churchill River. The evidence from this work however, is that
the larvae are actually killed; certainly no living larvae
were removed from any sampling screens, and since the exposure
period for released larvae moving downstream in the treated
water would be greater than that for those caught on the screens
or remaining attached, it is unlikely that any of them survive.

The duration of treatment has been recorded as
application period and. not as exposure period, since the latter
naturally increases with the distance from the application site.
The concentration, likewise, is that theoretically obtaining
at the application site; this figure undergoes a corresponding
decrease as the distance from the point of application increases.
At any given point downstream, the concentration increases
gradually to the maximum, and decreases again more gradually
from the maximum to zero, the rate of both the increase and the
decrease being less at greater distances downstream. There is
no evidence that these factors have any appreciable influence
on the mortality obtained for a distance of at least several
miles downstream.

The susceptibility of blackfly larvae to DDT appears

138

remarkable, until it is recalled that as a contact insecticide
this material normally has access to the tarsi, or at least
to restricted areas of the body only, whereas the whole of
the integument of the blackfly larva is exposed to DDT.

ihe application of DDT in oil solution from the air
at 0.25 lbs DDT per acre immediately before the first blackfly
pupae are lorraed, will effectively control for the season the
common arctic species of blackfly breeding in the area sprayed,
in screams up to lr> feet in mean depth. Heavier dosages might
be required for deeper streams. It would seem likely, that
with suitable delivery rates, a single swath applied along the
course of smaller streams, and a swath along either bank. with
the shore line as swath centre for the larger streams, would
prove equally effective, and this would be a very practicable
procedure.

Such a procedure, however, would involve greater
expense and, judging from the variety of insects killed, a far
greater interference with the balance of nature, than the
more laborious procedure of direct application to the streams.
Until the effects of this interference .are more fully under¬
stood, it seems desirable that the aerial method be employed
in special circumstances only. Similar mortality in diverse
groups of insects has previously been shown to occur as a result
of aerial spraying operations in Panama (2). Direct application
to streams of DDT in oil solutions to give one part in ten million
for 15 minutes caused remarkably little interference with other
life, but is somewhat more arduous and might have to be repeated,
the first treatment being given immediately before the start of
pupation, and the second two or three weeks later. Rarely is

•: . f r a-..

-

.

■

■

'

-

.

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.

139

there an opportunity to control an economically important
insect by using such an efficient, naturally provided, means
of distributing and insecticide as the flow of a stream.

Advantage should be taken of this opportunity. If further
studies confirm that gamma-BHC is an effective pupicide, it
might be possible to avoid a second treatment by applying a
mixture of DDT and gamma-BHC just before the emergence of the
first adults. This would increase the cost of materials, but
would reduce the labour cost and would interfere less with the
normal life of the stream.

The greater residual effect of treatment from the air
appears to be due primarily to the continued infiltration of a
very small concentration of DDT into the stream, washed off
rocks, the soil, and to some extent vegetation by rain and by
drainage water. Mortality of adults during and after the spraying
operation may be a contributary factor. A further possibility
is that, as Provost maintains, adult blackflies return to the
stream in which they matured to lay their eggs (43); the streams
treated from the air were the only ones which had produced no
pupae prior to treatment. However, the reinfestation of these
streams in July 1948, suggests that this tendency is not manifest,
at least in the earliest generation.

Some development of equipment is required for routine
direct application stream treatments. The requirements are, a
simple form of current meter to enable a ready and reasonably
accurate estimate of flow to be made, and a suitable dispenser.

The latter should consist of a stock tank to hold perhaps ten
gallons of material, leading to a flow meter consisting of a
differential pressure gauge and a variable orifice, controlled

*tift Hi.

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140

by a wheel valve. The* dispenser should be calibrated to give
the required flow of insecticide at each setting for a concen¬
tration of one part DDT in ten million parts of water, using
a ten per cent solution of DDT in fuel oil. The whole apparatus
should be designed to fit on a folding tripod stand which could
be set up in a small stream, on the bank, or in a boat. Two
men with this equipment and a paddle, stopwatch, measuring stick
and tape, could treat streams with a flow up to 250 cusecs
rapidly and conveniently, and the problem would by reduced to
the ever present problem of transportation. A shallow draught
boat with outboard motor would assist here, and the motor could
be employed also to secure good distribution of insecticide,
taking the place of a paddle in the larger streams.

What previous evidence there is seems to suggest that
the direct effects of DDT on animals other than insects in
ponds and tidewater are unlikely to be serious (59), even at
concentrations of one part DDT in three million parts water,
with exposure time limited only by the stability of the compound.
Observations during this work do not entirely support this view;
the possibility of accumulated concentrations of DDT in lakes
fed by repeatedly treated streams should not be lost sight of.
Indirect results can also be serious; blackfiy larvae for example,
form a significant food item of fish, especially suckers, which
are themselves important food of sled dogs.

1948 work with Insecticides against immature, stages
of Blackflies :

The much drier conditions in 1948, and the earlier
use of considerable areas of country for experimental spraying with

141

DDT from the air prevented extensive work with insecticides
in streams. The results obtained with DDT in 1947, were however
confirmed by applications to Eastern Creek, using the same
stretch of the creek again, and to Herriot Creek (708885),
flowing into the Churchill River from the west, some 25 miles
south of Churchill. In 1948 flow measurements were made with
a Gurley flow meter; the method used in 1947 was checked against
this meter, and gave figures agreeing within 5 per cent.

A preliminary test of a wettable powder containing
15 per cent “Parathion" ( o,o-di ethyl o-p-nitrophenyl thiophos-
phate) was made, and both this material and gamma BHC were
tested for toxicity to blackfly eggs. Results obtained in these
tests are summarised in tables 7 and 8.

The stream used in the first experiment has its origin
at 951054 and drains into a small lake on the tundra east of
Churchill camp. The water temperature at the time of treatment
was 62°F and the pH 7.5. Since this was a' new toxic material a
sampling screen was used; an analysis of a portion of the material
from this screen is as follows:

MOLLUSC A

Gastropoda

Pulmonata 3

aracemi DA
Acarina

J:Iy dr ac ari dae 3

CRUSTACEA

Branch! opo da 59

Copepoda 22

IUSECTA

Apterygota

Collembola - Arthropleona 8

Sxopterygota
Plecoptera

IT emou ri dae nymph s 87

Eph em eri da nym ph s 21

II end pt era

Co ri xi dae nymphs

1

142

TABLE 7. Summary of data from insecticidal treatment of streams.

1948

Experiment
No . and
date of
treatment

Observed treated length
of stream in yards.

I

i Average flow in cusecs }

_ _ _ ‘ 1

|

Insect ic ide

! i

formulation

Method of
appli -
cation

,

Concentration p.p.m.

i

L c I

Application time -- minaj

m

£

* »H

<D E
bfN.
ctf •

w £

o .

P P

Pu

population

.

Before treatment

24 hours after

treatment .

1. July 7

200

0.62

15%

Medi cine

-

0.2

15

3

! Moderate

Ml

Parathion

dropper

we tt able

powder

2. July 22

1400

30.8

10%

Graduate

0.113 !

15

1.7

Moderate

Ml

DDT in

fuel oil

3. July 24

5300

141

10%

Graduate

0.0695

15

1.04

Light

Ml

DDT in

fuel oil

* See explanation in Introduction to 5.1-3

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TABLE 8. The ovicidal properties of Parathion and Gamma
benzene hexachloride.

Insecti cide

Concen¬

tration

p.p.m.

Exposure

period

minutes

Dosage
p.p.m./
mins .

— —i

Per cent
hatch

Parathion

0.2

15

3.0

80

0.5

15

7.5

2

1.0

15

15.0

0.3

Gamma-BHC

0.2

15

3.0

83

0.5

15

7.5

15

1.0

15

15.0

4

Check

(untreated) 1,

„

88

2.

-

-

-

99.5

144

Endopterygota

Goleoptera

Dytiscidae 3

Trichoptera larvae 2

Dipt era

Nematocera

Chi ronorai dae larvae 5

pupae 3

adults 2

Heliidae

Culicoides sp. 2

Ti puli dae 1

Culi cidae

Aedes sp. 1

Simuliidae larvae 323

pupae 5

My c e t o pM li da e 2

In so far as it was possible to decide on a field examination,
the crustacean material was all alive at the time of collection,
24 hours after treatment; the insect material however, was
dead. Adults emerged from 6? per cent of pupae collected
before treatment, as compared with 25 per cent from pupae
collected immediately after treatment, and 20 per cent from
pupae collected 24 hours later, so that f,ParathionH appears
to have appreciable toxicity to pupae.

The second and third experiments confirmed the
effectiveness against larvae of DDT at 1.5 p.p.m. /minutes .

The length under observation in Herriot Creek (FIG. 37) was
greater than that in any 1947 test.

Both gamma-BHC and f,Parathionu especially, appear to
have useful ovicidal properties against blackflies. The L.D.

50' s for these materials are of the order of 4 and 6 p.p.m./
minutes respectively.

A. few tests against caged fish of insecticides
suitable for blackfly control were made in 1948. Neither
jackfish, suckers, nor sticklebacks were permanently affected

I

145

by dosages of DDT up to 300 p .p.ra. /minutes, although jackfish
especially became violently agitated after about six minutes
at the higher concentrations, and many were unconscious at
the end of the exposure. Suckers withstood 15 minutes in
"Parathion" at 1 part in 100,000.

Discussion; MParathion", by virtue of its apparent toxicity
to both eggs and pupae, and apparent harmlessness to stream
Crustacea, would appear to offer advantages over DDT. Its cost
however is greater, and it is believed to be much more toxic
to man.

5.2. Protection of the Person from Biting Fly Attack.

It is clear from the results set out in 5.1, that the
possibility of economical routine control of the numbers of
Aedes mosquitoes, at least of the migratory species (reputedly,
A. ni gripes. A. nearcticus, and A. camoestris ) by chemical
means is not very great. Even with DDT, to ensure freedom from
mosquitoes in a single locality would require an annual spraying
of an area of the order of at least a thousand square miles
( say a circle of 20 miles radius ), an operation which would
cost about a million dollars. As far as tabanids are concerned,
the chemical approach is even less encouraging, and it is only
against blackflies that this method seems at all hopeful.

The information available relative to the second approach

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to biting fly control is indicated in sections 1 to 3; it is
quite inadequate, as yet, for any but the most tentative
suggestions as to how this might possibly be initiated.

By elimination, there remains for consideration
only the third approach.

5.2.1. Repellents:

Although very great improvements in repellents for
biting flies have been made in the last few years by the
application of routine test methods on a very large number
of materials, further significant progress cannot be expected
without more fundamental work on the factors which attract
biting flies to their hosts, and on the mode of action of
repellents .

In 1947 a study was made of the relative effectiveness
of four standard insect repellents, twelve other liquid
repellents, and two repellent creams. Primarily, the study
was against Aedes mosquitoes, but the abundance of blackflies
in the areas used for tests, allowed simultaneous tests against
these insects. Accepted standard methods of test were
employed.

Of the standard repellents, dimethyl phthalate
afforded the longest protection against both mosquitoes and
blackflies, averaging 381 minutes and 393 minutes respectively.
Repellent mixture 6-2-2, which contains 6 parts dimethyl
phthalate, 2 parts Rutgers 612 ( 2-ethyl-l, 3-hexanediol ),
and 2 parts Indalone ( n-butyl mesityl oxide oxalate ), was

147

only slightly inferior to dimethyl phthalate in protection
time. Rutgers 612 afforded less protection against mosquitoes
than any other standard material, and repellent N.M.R.I. 448
( 30% 2- cyclohexyl cyclohexanol, 70% 2 phenyl cyclohexanol )
gave good protection against mosquitoes, but afforded less
protection against blackflies than any other standard.

Of the remaining materials, only n-propyl N,i\F-di ethyl
suceinamate afforded a protection time greater than that
given by dimethyl phthalate. It is doubtful whether the
improvement is sufficient to justify the adoption of this
material, should it prove sufficiently non-toxic.

All materials in use suffer from the considerable
drawback of being plasticisers, softening and dissolving
plastics, paints, and varnishes. Some of the inconvenience
of this could be avoided by eliminating these materials and
finishes as far as possible on equipment such as axe and other
tool handles, pencils, etc. which are regularly handled in
the open.

All observations made on repellents used while
working in the field agree in respect of two general conclusions.
These are, firstly, that there is little apparent difference
in the effectiveness of the four standard repellents tested
here, under conditions of actual use; and secondly, that with
a heavy and aggressive population of mosquitoes, and normal
activity of the subject in field work, the best of the repellents
may require renewal at least as often as once every hour.

Under very severe conditions; perspiration, working in water
or through heavy vegetation, the period of adequate protection
may of course be further reduced. The application of repellent

I q. • ’

.

.. = ; •• f .

■

.

■

.

.

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148

by hand to the outside of the clothing, particularly across
the shoulders, round the waist, and on the seat of the trousers
has material protective value.

The application of repellent in the field is awkward;
both hands are required, and if the bottle is set down, such is
the distraction of the biting fly attack that it is forgotten
with surprising frequency. The use of a liquid soap dispenser
for insect repellent was introduced by Mr. J. Myler of the
Edmonton City Parks Department, and proved very successful in
Golf clubs and Ball grounds in Edmonton during 1948. This
method could well be adopted in permanent military camps, such
dispensers being mounted at the outside doors of buildings, and
kept filled during the fly season.

Attempts to find repellents which can be administered
orally are not, as yet, promising; this idea was first
recommended by Ochman in 1911 (68), but little work has been done
on these lines until quite recently.

The term repellent is an unfortunate one, implying as
it does, an action at a distance which these materials do not,
in fact, exhibit. Modern repellents are .gustatory rather than
olfactory in their action; this fact, and the resulting
necessity for the application of a thin continuous film needs
to be pointed out to inexperienced users.

5.2.2. Protective Clothing and Shelters:

Many insects attacking man, are less inclined to do
so through clothing of non-animal origin, and this appears to

•

■

' •

■

J. i: f r f i': ;'W ' O'y.F.

!' ; : * • ■

■

v

-

.

■

'

149

apply to mosquitoes; many observers have recorded that biting
is worse through woollen fabrics than through cotton of similar
texture.

Extensive tests have been carried out with materials
of cotton and artificial fibres, mainly against nedes aegypti

and veiy satisfactory materials are known (3). These materials
are however mostly expensive and often uncomfortable to wear.
Annand et al (4) have found that coarse open mesh materials
worn underneath garments of highly permeable fabric prevent
the biting of A. aegypti in the laboratory. Field trials of
string vests, which are normal military issue in winter were
made during 1948, and worn under ordinary cotton twill shirts
gave complete protection under very severe conditions. This
arrangement proved much more comfortable than closely woven
materials. In this 1 distance piece* type of clothing, the
thickness of the open mesh material should, of course, be
comparable with the proboscis length of the mosquitoes concerned.
A. ni gripes has the longest proboscis of the Churchill Aedes
with 0.42 cm.

In general, the looser the clothing the less it is
bitten through; biting through is worst whenever and wherever
the cloth is stretched tightly over the skin.

Gjullin (23) has shown for several species of Aedes
that biting is worse through dark coloured materials than it
is through light coloured, and states that colours are chosen
on the basis of their spectral reflectances. Observations in
section 3.1.3 would seem to suggest that it may be spectral
absorption and consequently surface temperature which is the
deciding factor, rather than reflectance. Whatever the reason,

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150

lighter colours are certainly to be preferred.

Blackflies and tabanids do not bite through clothing;
but the former are very active and persistent in their efforts
to gain an entrance to the space between clothing and body.
Carefully designed closures are necessary to prevent this.

Properly designed clothing should reduce the psycho¬
logical as well as the physiological effects of biting flies;
that is, in addition to preventing biting, it should obviate
the necessity for the ’removal reaction', and should minimise
the impact of insects, at least on the face. The use of a fly
fringe - eye length in front and shoulder length behind - in
place of a net, might have advantages by virtue of its greater
mobility, in reducing the need for removal reaction at less
sacrifice of comfort and vision. Such a device would also be
less inclined to get caught in vegetation, and would suffer
less if it did so; the principle seems to be embodied in the
improvised headgear of some of the Churchill residents.

The impact of insects can only be eliminated by
wearing a head net, and if necessary, arm nets. It seems
reasonable to suggest that if a net has to be worn it might as
well be one which will exclude everything, including blackflies
and (possibly) no-see-ums, but cost is presumably a factor here.
Certainly, the comfort advantages of a wide mesh net do not more
than outweigh the necessity for keeping it doped with repellent,
and the inconveni ence of the occasional blackfly penetration.
There may be some advantage in a net held sufficiently clear of
the face to enable the eyes to focus on it, and hence also on
any insects which may alight on it. Arm nets have few advantages
and many disadvantages as compared with sleeves.

151

'The fly-proof shelter is a much neglected means of

providing relief from the attentions of biting flies 5 it is
the only single measure which will eliminate completely all
the elements of the biting fly attack. The psychological
effects respond to the provision of such a shelter as they
will to no other treatment.

Arctic biting flies in general are out-of-door insects;
they do not congregate in large numbers, even in relatively
unprotected buildings, nor do they cause such serious discomforts
when they are inside them. Accordingly it should not prove
difficult to render tents and shelters for use in the field
sufficiently fly proof for practical purposes, nor to design and
produce a special ’fly-refuge* for the use of field parties.

Such a structure should be light, quickly and simply erected, and
have plenty of headroom; a double door entrance to enable
users to get rid of their accompanying swarm of biting flies
before entering the main chamber is an advantage. The roof as
well as the walls should be of screening; a solid roof serves as
a great attraction to tabanids. Perfectly serviceable temporary
shelters have been improvised in the forest with no other materials
than a roll of cheesecloth, an axe, and a packet 01 tacks, and
have proved invaluable. The aerosol bomb as at present produced,
is a ready and efficient, if somewhat expensive, method of
clearing out such shelters when erected. The mere knowledge of
the existence of such a refuge, supplemented possibly by the
right to get into it for say, five or ten minutes in every hour
and relax, with flies kept at a distance, is of very great value
to men working in the field.

152

o.2.d. Other Aspects of Protection and Control:

Attempts have been made to immunise animals so that
ei tner mosquitoes will not feed on them, or that they will
not react to bites received, buch attempts are unlikely to
succeed until the factors which attract mosquitoes and the
causative agents of reaction to their bites are understood.

Dubin et al (18) worki ng with Anopheles quadrimaculatus and
rabbits succeeded only in sensitizing these.

With regard to the control of tabanids very little
work has been done. Neither the ’pools of death' nor the
carrying of black adhesive shields recommended by Porchinsky (77)
can be regarded as very practicable in circumstances such as
are encountered at Churchill. Traps as proposed by du Cordroy
(66) and by Criddle (69) appear almost equally unpromising
from the human viewpoint. A great deal more knov/led ge of
these insects is needed.

When the irritation of the bites of flies interferes
with sleep, some treatment is called for. Ammonia, washing
soda, iodine, and various ointments containing local anas-
thetics are in common use. Any application for this purpose
should have antiseptic properties to guard against secondary
infection., Hoffman (70) recommends the local application of
chloroform. Very hot water is an excellent counter irritant
for blackfly bites.

Next perhaps, to attempting to bathe (which can always
be postponed), the greatest discomfort from biting flies while.

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153

living in the open, arises during defecation. Palliatives
which have been found useful include a smudge fire immediately
to windward, and an aerosol bomb, set to discharge slowly, in
the same situation. Smudges, of course, are often impossible
under operational conditions, and an aerosol bomb, though
effective, is hardly economical. Certainly it is as well to
disregard the dictates of modesty, and to choose an exposed
windy situation.

It is felt that a big contribution to the solution
of the psychological problem could be made through an
indoctrination programme on the lines indicated by Shelesnyak
(51) . Superimposed on general arctic knowledge, should be some
knowledge of and interest in biting flies, imparted through
the normal media of training films, lectures, and popular
literature and pamphlets. Such knowledge while presenting a
true picture, should draw attention to the pleasanter aspects
of the species concerned - the relative improbability of disease
transmission, the acquired immunity resulting from bites, the
small amount of blood taken, and so on. The more interesting
gaps In our knowledge of these insects snould also be presented,
it is when the individual has nothing to do that the insect
menace is greatest; if he has an interest in the biting fly
problem, he will never have nothing to do when there are flies
about. The contributions to knowledge from such mass amateur
observations would probably be small, but the contri outions to
morale might be very great. Above all else, the importance o±
controlling the removal reaction should be stressed; there are
physiological (47) as well as psychological grounds for this

154

recommendation. Philip (42) has stated that interruption in
feeding results in regurgitation of blood from the mesenteron
into the oesophageal diverticula, a statement which has since
been confirmed by the work of Marshall and Staley (36) and of
Sumsden (34) . This suggests the possibility that such inter¬
ruption may also result in the regurgi tation of the contents
of the diverticula into the puncture.

In conclusion it may be stated that the psychological
threat of the biting fly can be greatly mitigated by the simple
cultivation of an attitude of patient tolerance; by learning
to accept these insects as an essential feature (at least for
the present) of an environment which, after all, offers many
compensations in other directions. Getting used to these
pests and * learning to live with them1 should be an essential
part of the training of all personnel for the north, since it
is certain that despite aeroplanes and DDT, and anything else
that these may immediately foreshadow, under operational
conditions at least, the biting fly will be an inseparable
feature of life in the north for many years to come.

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6. SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS
6.1. Summary of Control Conclusions*

Chemical insecticides offer no immediate economic
control of mosquitoes or tabanids. In special circumstances
such as a military emergency, when economic considerations
may be secondary, the application of DDT from the air at
0.5 lbs per acre will effect control of mosquito larvae.

Adult mosquitoes will also be controlled, but infiltration
into the sprayed area will be rapid.

Economic chemical control will require the development
of insecticides of markedly greater toxicity per unit weight,
or more probably, of more economical methods of distribution.

The latter may be achieved through the development of aerosol
generators with output of a new order of magnitude.

Blackflies may be controlled by the procedure for
mosquito larvae, or more safely and economically, by the
application of DDT in any form to streams, to give 1.5 p.p.m/
minutes, just before the beginning of pupation. A second dose
2 to 3 weeks later may be required. "Parathion" and gamma-BHC
offer possibilities for use against eggs and pupae.

There are no immediate prospects of control of any
of the three groups being secured through ecological means.

The most immediately hopeful approach is through

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156

protection of the individual and his immediate habitats. This
has two aspects; psychological, through training and cultivation
of a reasonable attitude to biting flies; physiological,
through the use of good repellents such as dimethyl phthalate,
proper protective clothing, and shelters in conjunction with
local insecticides.

8.2. Recommendations for Further Work.

A major result of most research is to demonstrate
the limitations of existing knowledge: some of the more
outstanding lacunae in this field are given briefly here.

The development of insecticides and distribution
methods are not mentioned; the biting fly problem alone hardly
justifies the expense entailed in this work, and the results
obtained are so generally applied that the work will, in any
event, continue.

Except where indicated, work on all of these problems
could proceed simultaneously.

1. The' factors affecting the hatching of mosquito eggs,
especially chemicaf factors.

2. The feeding habits of adult mosquitoes, other than on
the blood of man, and the relationship of these to
ovulation and oviposition, and to flight habits and
migration.

3. The food materials, feeding habits and behaviour of
larval blackflies. Mating habits, flight habits, and
feeding habits other than on human blood, of the adults.

4. Life histories, and especially larval behaviour and
feeding habits of the commoner species of tabanids.

.

.

. 1.j: : :: .

,

■

■

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-

157

5. The nature of the effect of biting flies on large
bodies of men, living in the open, and the relative
importance of psychological and physiological effects.
Also, the effect of such bodies of men on the biting
flies; is more men going to mean more blood meals, more
eggs, and hence more flies ?

6. The sensory physiology of all biting flies, especially
mosquitoes and blackflies, with particular reference to
the attraction of these insects to their hosts.

7. The nature of the toxic materials injected by biting
flies, especially blackflies, and the possibility of
combating these.

8. The mode of action of repellents, and the development
of better repellent chemicals. (After some progress has
been made on 5.)

9. The design, testing, and development of protective
clothing.

158

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2. Annand, P.N. et al. Insects killed by DDT aerial spraying in

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Report No. 108. 1945.

3. Annand, P.N., E.R.McGovran, and J.Lipton. Mosquito resistance

of 12 fabrics, JO cloths, Byrd cloth, and Oxford
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4. Annand, P.N. , J.P.Linduska, and F. A. Morton. Laboratory and

field tests on the permea.bili ty of fabrics to biting
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11. Brescia, F. and I. B. Wilson. Larvi cidal treatment of large

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37.

38.

40.

41.

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42. Philip,

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43. Prevost, G. Eradication of blackfly larvae for a long

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a serious livestock pest in Saskatchewan.

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51. Shelesnyak, M.O. Some problems of human ecology in polar

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54. Starling, E.H. Ibid. pp. 470 and 477.

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23: 261 - 304. 1930.

57. Strickland, E. H. Unpublished communication.

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use of DDT against mosquitoes in British Guiana.
Bull. Ent. Res. 37: 399 - 430. 1947.

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162

59. Tiller, R.E. and E.N.Cory. Effects of DDT on some tidewater

aquatic animals. Jour. Econ. Ent. 40: 431 - 433.
1947.

60. Twinn, C.R. The blackflies of eastern Canada. Can. Jour.

Res. D. 14: 97 - 150. 1936.

61. Twinn, C.R. , B. Hocking. , W. C. McDuffie. , and H.F. Cross.

A preliminary report on the biting flies at
Churchill, Manitoba. Can. Jour. Res. D. ( to be
published shortly.)

62. Wesenberg - Lund, C. Contributions to the biology of the

Danish Culicidae. D. Kgl. Danske Vidensk. Selsk.
Skrif'te, Nat. Math. Afd. , 8 Raekke. 7: 1 - 120.
1921.

63. Wigglesworth, V.B. The principles of insect physiology.

p. 83. Methuen and Co., London, 1939.

64. Wright, S. Applied physiology, p. 320. 7th Ed. O.U.P. 1940.

Supplementary References:

65. Cantrell, W. and H.B. Jordan. New mosquito hosts for Plasmodium

gallinaceum. Jour. Parasit. 31: 55 - 56. 1945.

66. Cordroy, M. R.L. Bourgault du. Trap for the destruction of

cattle flies. Jour. Roy. Amy Med. Corps 54:

208 - 211. 1930.

67. G-jullin, C.M. , W.W. Yates and H.H. Stage. The effect of certain

chemicals on the hatching of mosquito eggs.

Science 89: 539 - 540. 1939.

68. Graybill, H.W. Repellents for protecting animals from the

attacks of flies. U.S.D.A. Bull. 131. 1914. Abstr.
in Rev. App. Ent. (B) 3: 37. 1915.

69. Hearle, 1. Insects and allied parasites injurious to

livestock and poultry in Canada. Can. Dept. Agr.
Pubn. 604. p. 24. Ottawa 1938.

70. Hoffman, W.A. The effect of chloroform on some insect bites.

Science 94: 66. 1941.

71. Hunter, W.D. An unusual invasion of A. sollicitans in

Louisiana. Jour. Econ. Ent. 3: 504. 1910.

r.i.i

163

72. Longstaff, T.G. An ecological reconnaissance in West

Greenland. Jour. Anim. Ecol. 1: 119 - 142. 1932.

73. 0TKane, W.C. Blackflies in New Hampshire. New Hampshire

Agr. Exp. Sta. Bull. 32. 1926. Abstr. in R.A.E.

(B) 15: 193. 1927.

74. Olin, G. The occurrence and mode of transmission of

Tularaemia in Sweden. Abstr. in R.A.E. (B) 32:

56. 1944.

75. O'Roke, E.C. The incidence, pathogenicity, and transmission

of Leucocytozoon anatis of ducks. Abstr. in Jour.
Parasit. 17: 112. 1930.

76. Parker, R.R. Recent studies of tick borne diseases made

at the U.S. Public Health Service at Hamilton,
Montana. Proc. Pan. Pac. Sci. Congr. 5: 3367 -
3374. 1933.

77. Porchinsky, L. Tabanidae and the simplest methods of

destroying them. Abstr. in R.A.E. (B) 3: 195. 1915.

78. Roubaud, E. L’eclosion de 1 ? oeuf et les stimulants

d'eclosion chez le Stegomyia de la fievre jaune.
Abstr. in R.A.E. (B) 15: 161. 1927.

79. Roubaud, E. and J.Colas-Belcour. Nouvelles recherches sur

1T evolution experimental de Dirofilaria immitis
chez quelques culicides indigenes. Abstr. in
R.A.E. (B) 25: 250. 1937.

80. Rubtzov, I. A. Investigations on the use of mineral oil

emulsions for the control of blackflies. Abstr.
in R.A.E. (B) 33: 186. 1945.

81. Sanderson, E.D. Controlling blackfly in the White Mountains.

Jour. Econ. Ent. 3: 27. 1910.

82. Scott, J.W. Experimental transmission of swamp fever or

infectious anaemia by means of insects. Jour. Am.
Vet. Med. Assoc. 9: 448 - 454. 1920.

83. Thienemann, A. Die Stechmtlckenplage im hohen Norden. Abstr.

in R.A.E. (B) 27: 128. 1939.

84. Waterston, J. ' On the mosquitoes of Macedonia. Bull. Ent.
Res. 9: 1 - 12. 1918.

Studies on Dirofilaria immitis Leidy. Jour.
Parasit. 24: 192 - 205. 1938.

85. Yen, C

164

SELECTED BIBLIOGRAPHY

1. Beattie, M.V.F. Physico-chemical factors in relation to
mosquito prevalence in ponds. Jour. Ecol. 13:
67-80. 1930.

2. Blanchard, R. ^ Les moustiques. Histoire. naturelle et
medicale. F. R. de Rudeval, Paris 1905.

3. Brennan, J.M. The Pangoniinae of neartic America. Bull.
Univ. Kansas. 36 : 249 - 401. 1935.

4. Dunn, M.B. Methods of protection from mosquitoes, black-

flies and similar pests of the forest. Can. Dept.
Agr. Pam. 55 n.s. 1925.

5. Dyar, H.G. The mosquitoes of Canada. Trans. Roy. Can.

Inst. 13: 71 - 120. 1921.

6. Dyar, H.G. The mosquitoes collected by the Canadian arctic

exoedition, 1913 -18. Rep. Can. Arc. Exp. Ill
Pt. 0. 31 - 33. 1919.

7. Dyar, H.G. and R.C. Shannon. The north american two-winged flies
of the family Simuliidae. Proc. U.S. Nat. Mus.

69: 54 pp. 1927.

8. Edwards, F.W. On the British species of Simulium. Bull. Bnt.

Res. 6:' 23 - 42 and 11: 211 - 246. 1915, 1920.

9. Edwards, F.W., H.Oldroyd, and J. Smart. British blood-sucking

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10. Gjullin, C.M. A key to the Ae cries females of America north

of Mexico. Proc. Ent.'Soc. Wash. 48: 215 - 236.
1946 .

11. Headlee, T.J. The mosquitoes of New Jersey and their control.

N. J. Agr. Exp. Sta. Bull. 348. 1921.

12. Eerms, W.B. and H.F.Gray. Mosquito control. The Commonwealth

Fund. New York, 1944.

13. Hindle, E, Flies in relation to disease; blood-sucking

flies. Cambridge, 1914.

14. Hinman, E.H. A study of the food of mosquito larvae. Amer.

Jour. Hyg. 12: 238 - 270. 1930.

15. Hinman, E.H. Mosquitoes in relation to human welfare. Ann.
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165

16. Hinraan, E.H. Predators of the Culicidae. Jour. Trop.

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17. Howard, L.O. A remedy for gadflies. Porchinski's recent

discovery in Russia, with some American
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18. Howard, L.O., H.G.Dyar, and F. Knab. The mosquitoes of

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1912 -17.

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Mus. Bull. 68 and 86.

21. Kellogg:, V.L. Food of larvae of Simulium and Blepharocera.

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1938.

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Macmillan and Co., London, 1895.

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water biology. Amer. Viewpoint Soc. N.Y. 1927.

27. Philip, C.B. Methods of collecting and rearing the immature

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28. Philip, C.B. A catalogue of the blood- sucking fly family

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30. Reaumur, R.A.F.de. Memoires pour servir h I'histoire des

insect es. Histoire des cousins. 4: 573 - 636
1938,

31. Hemp el, J.G., W. A. Riddell, and E.M.McNelly. Multiple feeding

habits of Saskatchewan mosquitoes. Can. Jour.

Res. E. 24: 71-78. 1946.

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166

32. Smart, J. Insects of medical importance. Brit. Lus.

Nat. Hist. London, 1943.

33. stone, A. The horseflies of the sub-family Tabaninae of

the neartic region. U.S.D.A. Mi sc. Hub. 305.
1938.

34. Strickland, E.H. Some parasites of Simulium larvae and

their effects on the development of the host.
Biol. Bull. 21: 302 - 338. 1911.

35. Strickland, E.H. Some parasites of Simulium larvae and

their possible economic value. Can. Ent. 45:

405 - 414. 1913.

36. Theobald, F.V. A monograph of the Culicidae. Brit. Mus.

London, 1901-10.

37. Trager, W. On the nutritional requirements of mosquito

larvae. Amer. Jour. Hyg. 22: 475 - 493. 1935.

38. Twinn, C.R. Notes on some parasites and predators of

blackfli es . Can. Ent. 71: 101 - 105. 1939.

39. Ward, H.B. and G.C. Whipple. Freshwater biology. John

Wiley and Sons, New York, 1918.

40. Woodbury, E.N. Rearing insects affecting man and animals.

In: Chemical control of insects. Ann. Assoc,
for the Advancement of Sci . No. 20. 1943.

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167

APPENDIX A

#

Sight records of Birds and Mammals during the Fly Season
at Churchill:

Bi rds :

Gaviidae

Common Loon Gavia immer

Ardeidae

American bittern Botaurus lentiginosus

Anatidae

Canada goose Branta canadensis *

Pintail Anas acuta tzitzihoa *

Lesser scaup duck Ay thy a af finis
American golden eye Glaucionetta clangula
Red-breasted merganser Fergus serrator

Ac cl pitriidae .

Rough-legged hawk Buteo lagopus
Tetraonidae

Willow ptarmigan Lagopus lagopus *

Charadriidae

Semi -palm at ed plover Charadrius hiaticula

s emi p aim atu s *

Golden plover Pluvialis dominica dominica *
Scolopacidae

Hudson! an curlew Numenius phaeopus hudsonicus *
Hudsonian godwit Limosa hoemastica *

Wilson's snipe Capella g allin ago delicatula *

Ph al ar o p o di d a e

Northern phalarope Lobipes lobatus *

Red phalarope Ph alar opus fulicarius
Willet Catotrophorus semi palm atu s
Greater yellow legs Totanus melanoleucus *

Least sandpiper Eroli a minuti 11a

Semi -palmated sandpiper Ereunetes pusillus *

Stilt sandpiper Mi cropalama himantopus

Stercorariidae

Parasitic jaeger Stercorarius parasiticus

Laridae

Herring gull Larus argentatus
Glaucous gull Larus hyperboreus
Common tern Sterna hirundo hirundo *

Arctic tern Sterna paradis aea

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168

Tytonidae

Snowy owl Nyctea scandiaca
Short eared owl Asio flammeus

Alaudi dae

Horned lark Erenophila alpestris

Corvidae

Canada jay Perisoreus canadensis
Crow Corvus brachyrhynchos

Turdidae

Ho bin Turdus migratorius

Laniidae

Northern shrike Lanius excubitor borealis
Pringilli dae

Snow bunting Plectrophenax nivalis nivalis
White crowned sjoarrow Zonotrichia leucophiys *
Eastern tree sparrow Spizella arborea arborea
Pine grosbeak: , Pinicola enucleator leucura
Lapland longs pur Calcarius lapponicus lapponicus

( * Nesting )

M annuals:

Rodenti a

Porcupine Erethizon dorsatum
Muskrat Ondatra zibethica
Collared learning Dicrostonyx hudsonius
Muskeg meadow mouse Microtus drummondi
Varying hare Lepus americanus

4

Ungulata

Caribou Rangifer caribou

Cetacea

White whale Delphi napterus leucas

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169

A P P E N D I X B

An Insecticide Dispenser for Blackfly breeding Streams:

The dispenser is required to deliver a 10 per cent
solution of DDT in fuel oil at controllable rates to give a
concentration of DDT equal to one part in ten million parts
of the water of streams with flow rates up to about 250 cusecs.
The maximum tolerance permissible in this dosage, in view of
the possible danger to fish and other aquatic organisms is
considered to be plus* or minus 20 per cent. The most important
sources of error when treating streams are in the adjustment of
a dispenser to give the required dosage rate, and in the measur-
ment of the flow of water in the stream. An accuracy within 10
per cent can readily be obtained in the latter, even without the
help of a flow meter, so that a further error of plus or minus
ten per cent is permissible in the discharge rate of a dispenser.

The projected dispenser will give at least the required
accuracy at the low end of its range and increasingly greater
accuracy at higher flow- rates, so that the net risk will be
considerably less than that indicated by this figure. At the
same time any simpler design of dispenser, which could perhaps be
produced more cheaply, would require correspondingly more skilled
labour to operate and more time in operation.

The dispenser is designed for insecticidal fluids of
viscosity 5.0 centipoises ( the range of viscosity figures
quoted for fuel oil used in the North is 2.4 to 7.2 centipoises
at 50°F ), but with the aid of a calibration chart and a range

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mli is Is 99000 pipa itnnn ,o-o‘o*o ro: oil ,0000 bix/cw ? pinom or: oxocu nocoircnc

. ; - ,0 ■ ; O' ■ 0 - ' ."o' ' o; ' . r S'? ■- • 0 . .0 c 0-,, 0 ;'C, 0-0

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170

of orifices it would operate successfully at any combination
of temperature and intrinsic viscosity likely to be encountered.
The only dimensions where accuracy is of importance are those
of the tubing and of the orifices.

The container consists of a ten gallon drum with a
lid fitted with a gasket (B) and held in place by a wing nut on
a bolt welded to the centre of the base of the drum. An air
vent is required and could be conveniently drilled in the bolt
(A). The drum is fitted with three legs of g" M.S. rod splayed
at about 20° and extending about 15*' below the drum. About 3"
above the ends of these legs, which are pointed, are 2” collars
(E) which also serve as stops for 3' tubular extensions required
for use in the deeper streams. The outlet pipe, of -g” bore, is
placed half way between two legs about an inch above the base,
and a drain plug is fitted in the base opposite to this (F) .

The outlet leads directly to the flow meter shown on .
sheet 2, which is inserted at (G) in the drawing on sheet 1. This
consists of a threaded union to hold the interchangeable orifice
plates (J) , and a differential pressure gauge (G) connected, in
parallel and leading to a wheel valve (K) . For routine use
three orifices connected in parallel, each vdlth its own stopcock,
might be desirable ( shorn dotted (H) ), since the range which
can be obtained with a single orifice is only about 5 times,
but for an experimental prototype, so long as the orifice plates
can be readily interchanged by means of a knurled ring or wing
nut connection, this is not necessary. The differential pressure
gauge should give a full scale deflection with a pressure

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171

INSECTICIDE DISPENSER STREAM TREATMENT

Figure 39.

SHEET 2

172

difference equal to about 12" of water. It is understood that
very suitable gauges are available in the form of war surplus
air speed indicators for aircraft. The bore of the connecting
pipes to this instrument would be determined by the fittings
on the instrument; all other pipes should be of bore, except
that the final outlet should be arranged to discharge inside a
short length of wider pipe of sufficient bore to allow at least
l/16u clearance all round the outlet (D) . Four foot and six foot
lengths of this wider pipe, each with one end cut off at 45° and
a one foot length of oil resistant rubber coupling should also
be provided.

The theoretical orifice diameters required in plates
of 2 mm. thickness, determined from Poiseuille’s equation are:
low range ( for streams 2 - 10 cusecs ), 0.154 cms. medium range
( 10 - 50 cusecs ), 0.23 eras, high range ( 50 - 250 cusecs ),
0.344 cms., but for experimental purposes ten plates with
aperture diameters in the range 0.1 to 0.5 cms. should be
provided.

■