QUEENSLAND

BUREAU OF SUGAR EXPERIMENT STATIONS

DIVISION OF ENTOMOLOGY
BULLETIN No. 4,

On the Value of Poison Bait for Controlling
Cane Grubs

BY

EDMUND JARVIS,

Entomologist.

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BRISBANE:

By Authority: Anthony James Cumming, Government Printer.

QUEENSLAND

BUREAU OF SUGAR EXPERIMENT STATIONS

DIVISION OF ENTOMOLOGY
BULLETIN No. 4.

On the Value of Poison Bait for Controlling
Cane Grubs

EDMUND JARVIS,

Entomologist.

BRISBANE:

By Authority: Anthony James Cumming, Government Printer.

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Bureau of Sugar Experiment Stations,
Brisbane, 31st July, 1916.

The Under Secretary, Department of Agriculture and Stock, Brisbane.
Str,—I have the honour to submit for pubheation, as Bulletin No. 4
of the Division of Entomology of the Bureau of Sugar Experiment
Stations, the following notes on ‘* The Value of Poison Bait for Con-
trolling Cane Grubs,’’ by Mr. Edmund Jarvis, Acting Entomologist at
Gordonvale.
I have, &e.,

HARRY T. EASTERBY, General Superintendent.

FOREWORD BY GENERAL SUPERINTENDENT.

The following Bulletin by Mr. E. Jarvis is of such importance
that its immediate publication is deemed advisable even though the tests
made have been on the laboratory scale and not in the field. The urgeney
of remedial measures in connection with the most serious pest that sugar-
cane is subject to in Queensland is so great that the preparatory
methods suggested should be put into operation on a field scale at the
time advised—viz., about three weeks after the first general appearance
of the beetles. This Bureau will also have tests made on the field. The
cheapest method of sowing cow-pea would be by a seed drill such as
the ‘‘ Miss Dixie.”’

On the Value of Poison Bait for Controlling
Cane Grubs.

INTRODUCTORY.

Upon taking up the study of our most serious insect pest of sugar-cane,
the so-called Grey-back Beetle (Lepidiota albohirta, Water.), special
attention was naturally bestowed on the larval stage, which annually
occupies a period of about six months.

Control measures applicable to this important phase of its life-cycle
were briefly discussed in a previous report (Aust. Sugar Journal, Vol.
VIL., p. 140), mention being made at the time of a dozen feasible methods
of procedure of more or less economic value arranged under the head-
ines—‘‘ Remedial,’’ ‘‘ Preventive,’’ and ‘‘ Natural Control.”’

Before starting to fight a pest of this kind, a knowledge of its life-
history and economy is, of course, essential.

In the present instance we have much to learn regarding the habits
of the grub, but may, I think, assume its subterranean movements to be
affected by various tropic influences other than those directly associated
with the act of nutrition or with climatic changes.

Probably every grower is familiar with at least two of the principal
actions of this pest, viz—(1) that of eating cane roots, and (2) of con-
tinually passing quantities of soil through its body. These well-known
habits were thought to constitute a fitting basis on which to commence
experimentation of a remedial nature, a brief account of which will now

be given.

Larvicides.

Research work in this connection was started in February, 1915,
when a number of insecticidal solutions were applied to cages containing
larve of albohirta, with more or less satisfactory results (see Aust.
Sugar Journal, Vol. VIII., p. 62). The drawbacks to such a method of
control, however, were early realised, and the work abandoned in favour
of more hopeful measures.

The question of poisoning the grub by means of arsenicals, Ke.,
appled to the soil appearing worthy of investigation, a series of experi-
ments were undertaken along this line, the knowledge cbtained being in
some instances of economic value.

Fig,

Fig.

On the Value of Poison Bait for Controlling Cane Grubs.

EXPLANATION OF PLATE.

1.—Eges of the “ Gray-back” Cane Beetle (Lepidiota albohirta, Water.)
a week after deposition (original),

2—Larva of same, third moult, about three-quarters grown (original),

3.—Venter of anal segment of larva, showing disposition of setse or
bristles, by means of which grubs of this beetle may be readily
distinguished from those of other closely related scarabeide
(magnified about six times ; original).

4.—Mandible or jaw of grub (magnified four times ; original),

5,—Abdominal spiracle and peritreme of grub (magnified seventeen

times; Original),
6.—Pupa of same, dorsal aspect (natural size ; original),

7.—Abdominal segments of pupa, Nos. 7-8, illustrating the appearance

of dorsal strie and anal horns (twice natural size; original),
8.—Adult female of ‘* Gray-back” Beetle (natural size ; original),

9 —Cane grub injury to roots and underground portion of stalks of nine-

months’ old ** Goru” (half-natural size; original),

On the Value of Poison Bait for Controlling Cane Grubs. 3

has '
Ce UL a Wir We

fe Al I i vy dy
Pp EE ML EU TA NANO
PREVA T ANN AAR
PA te OA ‘
Meee

E. Jarvis, Del.
CockcHarer BEETLE oF Sucar Cane (Lepidiota albohirta, Water).

(Its metamorphosis, ete., and mode of injury.)

4 On the Value of Poison Bait for Controlling Cane Grubs.

Poisoning the Soil.

Grubs placed in moist earth containing aceto-arsenate of copper in
the proportion of 2 0z. to one cubic foot (infected by thoroughly mixing
the dry poison with sifted soil) remained normal throughout the course
of these experiments, while the same chemical administered at the rate
of 8 oz. to a cubic foot was quickly fatal to 100 per cent. London purple
(8 oz. to 1 foot) proved effective, but less deadly than the foregoing
arsenical. Carbide lime, sulphur, and several other chemicals gave
negative results. This mode of application appeared out of the question
owine to excessive cost of both labour and materials, so further research
was postponed, pending the possible discovery of a more suitable sub-

stance possessing manurial properties.

POISON BAIT AS A MEANS OF CONTROL.

The great importance of experimentation in this connection was
recogmsed from the start and kept in view throughout the course of the
above-mentioned preliminary research work initiated last year, which, in

fact, served as a stepping-stone to more extended investigations,

Our cane grub being voracious in appetite, and what is termed a
eross feeder, it seemed highly probable that it would swallow almost
any kind of poison providing its odour was not obnoxious and the bait
used sufficiently attractive. Later experiments, to be touched on pre-
sently, amply demonstrated the correctness of this assumption.

The first step was to discover some vegetable substance that, whilst
not auickly decomposing when buried in the soil, would at the same
time be palatable throughout a period of three weeks or longer, either in
a fresh form or as vegetable humus. In addition to the foregoing
qualifications, this desirable substance had, above all, to be cheap, readily
obtainable in bulk, and easy to apply.

As a result of numerous experiments it was found that larve of our
Mealy-back Cane Beetle would eat many kinds of roots, &¢., and were
apparently very partial to the tubers of both English and sweet potatoes,

cuctunber skins, and thin slices of cane stalks sectioned transversely.

In May, 1915, whilst watching some ploughing operations on land
that had recently been green manured, it suddenly occurred to me that
here, perhaps, was the key to the situation—viz., the employment of
either Mauritius bean or cow-pea as a bait, which, in addition to the
possession, possibly, of all the above-mentioned requirements would act

also as a manure, and so help to reduce the expense of appleation.

On the Value of Poison Bait for Controlling Cane Grubs. 5

Investigations were at once entered upon, and proved conclusively
that grubs of our Cane-beetle will readily devour the leaves of both
these plants.

Finding cow-pea to be the more attractive, experiments were con-
ducted to determine the rate of decay of foliage of this legume when
buried at a depth of about 9 inches, and also with a view to rendering
its leaves still more palatable. Before attempting to study the latter
point it was necessary to undertake a long series of experiments, that
need mot be mentioned here, for the purpose of discovering an efficient
poison. Results for many months were unsuccessful, owing to the
extreme resistance of our cane grub to stomach poisons. Baits treated
with arsenical sprays of more than thirty times the strength usually
recommended for plant-eating insects failed to produce serious effects,
and for a time it seemed likely that this pest might ultimately be found
to be altogether proof against the cheaper forms of arsenic administered
in this manner. However, towards the end of February last I determined
to try the effect of dust sprays, apphed, as a supreme test, at full
strength.

Now, in a problem of this nature a poison to be suitable needs, in
the first place, to be very deadly, and at the same tine sparingly soluble,
so as to withstand the action of heavy rains which would weaken and
soon lessen the efficieney of quickly soluble chemicals. Aceto-arsenate of
copper (Paris green) appeared to be more fitted for the purpose than
some of the other arsenical compounds, and although previous experi-
ments with it in 1915 had failed, 1 decided to give it another chance
under the most favourable conditions. Results secured last February,
1916, by the first of these tests proved very encouraging.

Cow-pea foliage was sprayed on the upper surface with mill molasses

(1 pint to 3 pints water), and then dusted with the arsenical by sifting

it through coarse linen. The experiment comprised eleven cages, each
containing 20 cubic inches of fresh soil and a grub, nine supplied with

a poisoned leaf and the remaining two being controls with unsprayed
leaves, the foliage in each case being buried about 2 inches deep. An

examination made twenty-four hours later showed 70 per cent. of dead
larve in various stages of decomposition, which had between them con-

sumed less than three-quarters of a square inch of the poisoned leafage.
Subsequent examinations up to 10th February gave a mortality of 90 per

cent. in sixteen days. This important experiment was at once repeated

on 24th February, with seventeen treated and four control cages con-

taining first and second stage grubs confined with poisoned cow-pea

leaves, cut up in various forms as recorded by the following table :—

Bait for Controlling Cane Grubs.

On the Value of Poison

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On the Value of Poison Bait for Controlling Cane Grubs. 7

Suminarising results shown by the foregoing figures, it was found
that ten out of seventeen grubs placed with poisoned leaves were dead
and partially discoloured a day after treatment, and by the end of fifteen
days 100 per cent. had perished, controls remaining perfectly normal.

The above result was, of course, highly satisfactory as far as it
went, but it was necessary to determine how lone these leaves would
continue palatable and the insecticide effective when subjected to damp
conditions underground. Foliage that had been poisoned for this pur-
pose and then buried 6 inches deep between rows of cane was accordingly
dug up after the lapse of a fortnight, and discovered to be more or less
rotten, the leaves having quite lost their rigidity. Fungi were present,
but the soil in contact with the surface of the leaves was not matted
with mycelium to a serious extent, as frequently happens with other
vegetable baits of a more or less starchy nature,

On the 8th of March fragments of these decaying leaves were placed
in six cages with second stage grubs of Lepidiota albohirta (table omitted
here for sake of brevity), and when examined fourteen days later all
were dead. Thus it was proved that cow-pea foliage poisoned with
copper arsenate will remain palatable and deadly in the ground for at

least twenty-seven days.

The question of application was the next step, and I concluded that
the simplest way, requiring least handling, would be to sow the peas
in a single line about 1 foot from the stools on each side of a row of
eane, and when the resultant plants were a few twnches high, dust and
plough them under in such manner as to bury the poisoned leaves against
the main roots of the cane, where grubs when moving about in the soil
would be most likely to meet with them. The adoption of this method,
however, would necessarily entail an appreciable loss of material, it being
impossible to treat the foliage without at the same time dusting the
surface of the ground to some extent. For several reasons it seemed
wisest to adopt the above-mentioned simple method of application, and at
the same time reduce expenditure to a minimum by diluting the chemical.

In the following table it will be seen that Paris green mixed with

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three times its weight of stale flour proved fatal to about 98 per cent.
of cane grubs in one week, 75 per cent. in fifteen days, and 100 per cent.

after the lapse of twenty-five days.

Bait for Controlling Cane Grubs.

On the Value of Poison

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On the Value of Poison Bait for Controlling Cane Grubs. 9

The experiment shown in Table II. was repeated on 12th April with
sixteen grubs, but using leaves that had been similarly treated on 22nd
Mareh and left for three weeks lying in damp soil. The result was a
mortality of 45 per cent. in twenty-one days, demonstrating that leaves
dusted with copper arsenate and flour (1-3 formula) retain a marked
degree of effectiveness after remaining in the ground for about five
weeks,

WHITE ARSENIC BAIT.

Having secured such good results with arsenate of copper, I decided
to experiment with arsenious acid, commonly known as white arsenic,
which, although more soluble in water than Paris green, is much cheaper,
and has the additional advantage of being very conspicuous in the field.

In the first experiment, started 25th February with six infected and
two control cages, the arsenical was applied in undiluted form as a dust
spray, with most encouraging results. It was sifted through butter cloth
on to cow-pea leaves moistened with mill molasses solution (1-3 formula),
and 2 square inches of the poisoned leafage placed in each treated cage
enclosing a second stage grub of albohirta in 20 cubic inches of soil. A
mortality of 100 per cent. was obtained in ten days, the amount of
poisoned leafage eaten collectively by the six dead grubs being about
1 square inch. Controls remained perfectly normal throughout. This
experiment was repeated on 14th March with fohage that had been
poisoned on 25th February and buried for eighteen days between rows of
sugar-cane. These leaves when dug up were in a semi-rotten state, and
more or less interlaced by slender cane roots, that appeared to be deriving
nourishment from them. Portions of this decaying vegetation were then
placed with cane grubs in five cages of soil, and by the end of fourteen
days had caused a mortality of 100 per cent., proving that this arsenical
retains its efficiency underground for at least a month.

WHITE ARSENIC versus PARIS GREEN.

Desiring to ascertain the effect of diluted white arsenic, an experi-
ment was started on 24th March identical in construction with that given
in Table If., the only difference being the employment of this arsenical
in the place of Paris green.

Detailed results need not be tabled here, it being sufficient to state
that after a lapse of three weeks the death rate did not exceed 33-30 per
cent.

Compared with copper arsenate, the effect obtained may be sum-
marised thus :—

Paris Green (1-3 formula )—

In one week killed 58 per cent. of grubs.

In two weeks killed 75 per cent. of grubs.

In three weeks killed 91-60 per cent. of grubs.
White Arsenic (1-3 formula)—

In one week killed 16 per cent. of grubs.

In two weeks killed 25 per cent. of grubs.

In three weeks killed 33-30 per cent. of grubs.

10 On the Value of Poison Bait for Controlling Cane Grubs.

In spite of this failure in diluted form the claims of arsenious acid
as a suitable insecticide for fighting the cane-grub deserve recognition,
owing to its being fully six times as cheap as Paris green; for we have
already seen that both these arsenicals when undiluted occasion about
the same percentage of mortality.

The quicker action of Paris green may prove to be an unimportant
factor in the present instance, since grubs affected by either poison prob-
ably cease feeding, and provided that all ultimately perish it matters
little whether some die sooner than others.

Owing to the greater solubility of arsenious acid and its burning
action on foliage, it is seldom recommended as an orchard spray unless
in combination with lime or various chemicals; but, again, such draw-
backs do not necessarily apply to its application underground in a dry
form, although possibly during wet weather fohage dusted in this way
may rot more quickly than would be the case were it treated with copper
arsenate. If deemed advisable the soluble arsenates in commercial white
arsenic could be easily rendered insoluble.

There is no necessity, however, to discuss the subject more fully
just now, but I may mention than in addition to its trifling cost this well-
known arsenical is considered to be less poisonous to man than Paris
ereen, and, as a rule, is freer from adulteration with foreign substances.

MODE OF PREPARING AND ADMINISTERING THE BAIT.

The most favourable time to start the preparatory work of drilling
in cow-peas for bait would be about three weeks after the first general
appearance of Gray-back Beetles, as we should then disturb the soil
shortly after oviposition and probably break up many egg chambers. In
the event of an occurrence of protracted dry weather it might be found
advisable to sow a little sconer in order to take advantage of moisture
still remaining from the heavy rain that usually ushers in the first
emergence of these beetles.

Having got the peas to germinate and ceme up, their after growth,
if retarded, would not matter much, our object being to obtain stocky
plants, bearing, say, a dozen leaves, and together making a compact line
of fohage about 6 inches high by 8 inches broad. Should the rows exceed
these dimensions, a month after sowing they could be dusted and
ploughed under in the manner already described on page 7. but if
dry weather should happen to keep the plants stunted it would be better
to allow six weeks from date of sowing to elapse before treatment. as cane
grubs would by that time have moulted to the second stage, in which
they manifest a greater hking for vegetable food and acquire increased
powers of locomotion.

To ensure complete burial in the most favourable position, it might
be found necessary to plough a trench close alongside the stools, sow the
peas in the bottom, and later on, after dusting the plants, turn a furrow
on top of them, the weight of which would tend to press the poisoned

leaves downward to the requisite depth.

On the Value of Poison Bait for Controlling Cane Grubs. 11

In addition to the foregoing advantage, this method of burvine the
bait would ensure the destruction of numerous eges, and, moreover,
provide ideal conditions for the germination and after development of
the cow-peas, which, if sown near the surface, would be more likely to
suffer from dry spells that sometimes occur about the beginning of the
year.

The dry method of administering insecticides is not only cheaper
but far more convenient than spraying with liquids in the ordinary way.
Various mechanical contrivances and powder bellows have been specially
designed for this class of work, but in the present instance the usual
pole and bag method would, I think, meet requirements. With this
simple appliance, consisting of a wooden bar about 4 feet lone with a
cloth bag fixed at each end to contain the insecticide, a man could treat
from 3 to 4 acres a day, doing two rows of peas at a time by merely
walking between them and slightly jarring or shaking the stick so as to
cause a fine cloud of dust to settle down on the plants. Such application
should be made either at night, late in the evening, or in the early morn-
ing when there is little or no wind and the leaves are wet with dew.
By observing certain rules the work is performed without risk to the
operator, and danger is well-nigh impossible, as the powder is shaken a
few inches only above the ground and over a very limited area.

COST PER ACRE.

Seeing that our cane grub is far harder to kill than any species of
leaf-eating caterpillar, dusting operations, although limited to a narrow
band of verdure, would need to be done thoroughly.

The comparative cost of material per acre for both arsenicals works
out approximately as follows :—

Copper arsenate (undiluted), 8 Ib. at Is. 6d.=12s. per acre.

Copper arsenate and waste flour (1-3 formula), 2 Ib. at 1s. 6d.—=3s.
per acre.

Arsenious acid (undiluted), 10 lb. at 3d.=2s. 6d. per acre.

To this must be added the value of the cow-pea seeds, which at the
present market rate of about 18s. a bushel would be something like 10s.
per acre; these, however, could no doubt be grown by the farmer for
much less than it would cost to purchase them. Presuming that a man
could dust 4 acres a day, the outlay for such labour would amount to
about 2s. 6d. per acre; but this item, including expenses entailed by
sowing the peas and covering in the poisoned plants, wouid, I presume,
be counterbalanced by advantages derived from the breaking up of egg-
chambers, destruction of weeds, improvement of both land and cane by
extra culture, and lastly by the nitrogen added to the soil by the peas.

It is unnecessary at present to give more than a rough estimate of
the total cost per acre for labour and material, which apparently would
not exceed 12s. 6d. for the white arsenic treatment, and probably less
than 10s. if the cane farmer were to grow his own cow-peas.

12 On the Value of Poison Bait for Controlling Cane Grubs.

CONCLUSIONS.

It must be borne in mind that results now recorded relate exclusively
to cage experiments, and have yet to be confirmed in the field. Apart
from such considerations, however, the present Bulletin, which announces
a cheap, simple, and presumably effeetive means of combating the grub
stage of our most serious cane insect, cannot fail to be of interest to all
concerned in the sugar industry.

At the risk of being thought too optimistic, I do not hesitate to say
that future field investigations in this connection are not likely to reveal
the presence of any vital obstacle to final success.

The chief points requiring settlement by such field work will relate
primarily to the question of rainfall, and its effect on the solubility and
efficiency of both forms of arsenical; and to various operations of a
mechanical nature which will enable us to determine the simplest and
most economical method of dusting and burying the poisoned cow-peas.

It need scarcely be stated that the plan of procedure outlined in this
Bulletin relates solely to treatment of the late crop, which at Gordonvale
is planted from August to October, and is the one principally attacked.

It is my intention to combat the larva as far as possible during its
second stage, at a time when young plant and ratoon cane would not
be high enough to interfere with the field work connected with this
control method.

With reference to the behaviour of the grub under natural con-
ditions, it is well known that although leading a subterranean life it
constantly changes its position, becoming especially active during wet
weather; hence we may reasonably assume that while travelling among
the main roots, feeding, and ingesting soil, it can hardly fail to encounter
the bait before able to work appreciable damage.

Rich voleanie soils of a deep and friable nature afford ideal con-
ditions for the development of cane grubs, and it 1s worth noting that
this class of land—seen at Greenhills, Meringa, and other districts—is
precisely the one most likely to benefit from the application of poison
bait, owine to the fact that grubs are able to move about in it with
facility.

Field experiments cannot be expected to yield percentages of
mortality as high as those shown on the accompanying tables, for the
simple reason that grubs confined in small cages of soil must perforce
soon discover the bait, whereas, under natural conditions, owing to the
very erratic movements of the pest and the presence of other vegetable
food, a larva might on oceasion feed for days close to poisoned leatage
without perceiving it, or even miss it altogether. Unquestionably, this
would seldom happen if the treated leaves were artificially rendered
enticing enough to induce grubs located within a radius of from 4 to
6 inches to move towards them.

On the Value of Poison Bait for Controlling Cane Grubs. 13

It is proposed to investigate this question next season by studying
the underground tropic reactions of the larva, or, in other words. the
reflex acts or combination of such, induced mainly by the moisture,
temperature, and physical character of soils, and which are probably
influenced in some degree by other comparatively obscure forces of a
chemotropic or olfactory nature. It will be of interest to mention in
this connection an important cage experiment conducted in May (1916)
to discover whether grubs would eat this bait if it were closely sur-
rounded by cane roots.

Larger cages holding 60 cubic inches of soil were used, and the
bait (about 2 square inches of leafage) placed just below a mass of
living roots, arranged so that the caged grub would encounter its natural
food first, and be obliged to pass among it to reach the poisoned leaf.
Twenty cages were treated in this way, ten with copper arsenate bait and
the remainder with arsenious acid, each enclosing a large third stage
larva of our Gray-back Beetle.

Results revealed by subsequent examinations proved eminently
satisfactory in the case of the former arsenical, which in forty-eight
hours had occasioned a mortality of no less than 60 per cent., followed
by 90 per cent. in three days, and 100 per cent. in a week. The ten cages
containing white arsenic bait yielded 60 per cent. of dead grubs after
twenty days.

The season is now too far advanced for further investigations
relative to the larval stage of cane-beetles, but this last experiment, and
indeed the results of previous research work as a whole, illustrate the
very deadly nature of arsenate of copper in undiluted form, and incline
me to think that it may ultimately prove to be the best insecticide for
our purpose.

In the event of field experimentation next season being successful,
we may consider one phase of the cane grub problem as practically
solved; but, unfortunately, in the present instance are dealing with an
indigenous insect that breeds in untold numbers over a vast portion of
Northern Queensland, and must remember that whatever form of contro]
may be adopted in the future, whether preventive or remedial, we cannot
eradicate this pest, but only hope, at the best, to effectually combat its
ravages on limited areas devoted to the cultivation of sugar-cane.

NOTE BY GENERAL SUPERINTENDENT.

In reply to question as to the possibility of the grubs attacking the
cow-pea roots and perhaps destroying the plant before it could be dusted
and ploughed under, Mr. Jarvis has supphed the following notes :-—

‘* T think that although individual cow-pea plants might suffer from
erub attack, such damage would not be sufficient to seriously interfere
with the experiment.

14 On the Value of Poison Bait for Controlling Cane Grubs.

‘The question, of course, is one that can only be absolutely settled
by field tests, but my view, as stated above, is based on the following

conelusions :—

(1) The eggs would have been iaid before the planting of
the peas, and seeing that the beetles, as a rule, oviposit either
close to the stool or directly under it, the chances are that the
resultant grubs whilst very smail would not travel that far, but
feed on the fibrous cane roots close at hand.

(2) Drawing the trench for planting of peas would, as I
have intimated in m.s., probably destroy most of the egg cham-
bers formed by beetles at a distance of from 6 to 12 inches from
the stool, and so minimise chances of attack from grubs located
in that situation.

(3) By sowing the peas in the bottom of a deep trench as
suggested in ms. they (the plants) would be obliged to root in
a lower strata of soil than that in which eggs are generally
deposited, and being at a lower level would not only be isolated,
as it were, from direct attack, but situated partly on subsoil of
too firm a nature to admit of easy access from first and second
stage grubs; moreover, grubs, as a rule, prefer to travel in loose
soil, which they are continually ingesting for the sake of extract-
ing the organic matter.”

3y Authority: ANTHONY JAMES CUMMING, Government Printer, Brisbane.

HLL