.

wt

ENT oO. 87. Issued June 3, 1907.

aited States Department of Agriculture,

BUREAU OF ENTOMOLOGY,

L. O. HOWARD, Entomologist and Chief of Bureau.

THE COLORADO POTATO BEETLE.

é
(Leptinotarsa decemlineata Say.2)

By F. H. CHITTENDEN,

Entomologist in Charge of Breeding Experiments.

There are few more familiar insects to the farmer and others who
lead a rural life than is the Colorado potato beetle, or “ potato bug,”
as it is commonly known; and yet scarcely more than forty years
ago the potato crop of the United States had no very important insect
enemy. Not many years later this insect had, by its depredations on
potato, one of our most valuable food staples, caused as great concern
as have the San Jose scale and cotton boll weevil in the past decade,
and was also the subject of much study and experiment. Although
so common an insect,
many are not thor-
oughly acquainted
with its life history
and habits and with
the best methods of
combating it, and this
apples particularly to

persons farming in Fis. 1.—Colorado potato beetle (Leptinotarsa dece mlineata): a,
Beetle; b, larva; c, pupa. Enlarged (original).

districts only recently
invaded by the foe. The insect is continually extending its range
southward, and many complaints are received from localities where
the pest has not become thoroughly acclimated.

The potato beetle, notwithstanding all that has been done to
suppress it, is still a pest of great importance. It is interesting as
the first known example of an insect native to our Western States
being introduced eastward and thence practically all over our country
and Canada (except on the Pacific coast) where potatoes are grown.
In its early days as a migrant there seemed to have been no check to its
eastward spread other than natural barriers, such as rivers and lakes
and the Atlantic Ocean, but in the course of years numbers of nat-
ural enemies—birds, mammals, and predatory and parasitic insects—

aFormerly classified and better known as Doryphora 10-lineata-Say.
30546—No. 87—07

9)

have learned to attack it, and, in the case of the insects, they have
multiplied until now they are recognized as important factors in
the control of the beetle. The species is interesting also as having
led to the first use of an arsenical insecticide, Paris green, on edible
plants. Fortunately, with a knowledge of the habits of this insect,

SS WN
OSKS MY .
) a OYE
5
~

————>
SS

. Ss x

Vic. 2.—Section of potato plant showing Colorado potato beetle at work: a, Beetle; 0,b,
egg masses; c,c, half-grown larvee; d,d, mature larve. Somewhat enlarged (original).

the use of arsenicals, and the friendly assistance of natural enemies,
the grower may hold it in practical subjection.

DESCRIPTIVE.

The Colorado potato beetle is so well known that a description
seems hardly necessary for most persons, but that there may be no
[Cir. 87]

3

- danger of confusing it with any related species or with beneficial
ladybirds, a few words of description may be given.

The beetle (fig. 1, a; fig. 2, 2) is of robust form, about three-eighths
of an inch in length or a little more, and two-thirds as wide as long.
It is ochreous yellow in color, and the wing-covers are ornamented
with ten longitudinal black lines. The head is marked with a
triangular black spot, and the thorax is dotted with ten or more
irregular spots and other markings. The lower surface is also more
or less marked with black, particularly the tarsi
and knees. :

The larve (fig. 1, 0; fig. 2, cc, d,d) are quite as
weli known as the beetles and are very commonly
called “slugs.” They are dark Venetian red
when first hatched, and as they approach maturity
become paler. They are slimy, disgusting looking
creatures, soft m texture, and from their peculiar
coloration and appearance would not be readily
handled by anyone without gloves.

The pupa is red like the larva and looks as
Shown at ¢ figure ne

The eggs (fig. 2, 6,0) are orange colored and are _ ta),an “old-fashioned

deposited in masses. potatos Esa is
thor’s illustration. )

As this beetle is sometimes confused with one or
another of the “old-fashioned potato bugs” (blister beetles), a
species of the latter is illustrated here for comparison (fig. 3).

ORIGIN AND DISTRIBUTION.

Tt has always been believed—and, the writer maintains, with rea-
son, until the contrary can be proved beyond doubt—that the Colo-
rado potato beetle, having become dispersed from Colorado as a start-
ing point, originated as a species in that region. Dr. W. L. Tower,
however, in a publication issued in 1906,¢ has assumed that this insect
had the same origin as its principal wild food plant, Solanum rostra-
tum, which he states is essentially tropical, and that the insect has
followed the distribution of the plant from Mexico into Texas, New
Mexico, and parts of Arizona. He also gives reasons for the belief
that Leptinotarsa decemlineata has developed from L. “ intermedia
Tower” after changing its habitat, the latter occurring in both
Mexico and Texas, and the former not being found in Mexico at all,
according to his experience.

HISTORY OF THE INSECT’S SPREAD.

The eastward dispersal of this potato beetle from what is generally
considered its original home in the West is of peculiar interest. The

«An Investigation of Evolution in Chrysomelid Beetles of the Genus Lepti-
notarsa, Carnegie Institution, Washington, D. C., pp. 25 et seq.
[Cir. 87]

+

beetle appears to have been first associated with injury to potato in
1865. Forty-five years prior to that time it had been recognized as
feeding on the sand bur, or beaked nightshade (Solanum rostratum
Dunal.). a related solanaceous plant peculiar to the Rocky Mountain
region. The beetle was described in 1824 by Thomas Say. With
the advance of civilization westward and the cultivation of potato in
the vicinity of its native home, the insect acquired the habit of feed-
ing upon this more succulent plant, and about 1859 it had spread to
the east as far as Nebraska. Two years afterwards it reached Kansas,
and later Iowa, which it traversed in three or four years; so that by
1864 or 1865 it had crossed the Mississippi River and invaded the
western borders of Illinois. In its spread through Illinois it was de-
scribed by Walsh as marching through that State “in many separate
columns, just as Sherman marched to the sea; the southern columns of
the grand army lagged far behind the northern columns.” By 1869
it had found its way to Ohio, appearing almost simultaneously in the
northern and western portions. During all this time, beginning with
the year 1861, the insect had done considerable injury, and by 1870 it
had become exceedingly destructive in the North and Middle West,
and was continuing its eastward march at an increasing rate. It
had now reached the Province of Ontario. By 1872 its depreda-
tions in the West had noticeably abated, owing to the effectiveness of
natural enemies and to the increasing use of Paris green! _ Its prog-
ress eastward, however, continued, the northern columns becoming
established in Pennsylvania and New York, the southern ones reach-
ing Kentucky. The next year it made its first appearance in the Dis-
trict of Columbia and West Virginia, and in 1874 it had reached
the Atlantic seaboard and was reported from Connecticut to Mary-
land and Virginia.

3y the centennial year (1876) the Colorado potato beetle had
spread over an area composing more than a third of the United
States, so that it occupied at that time more or less completely the
States of Colorado, Nebraska, Kansas, Minnesota, Iowa, Missouri,
Wisconsin, Illinois, Michigan, Indiana, Ohio, Kentucky, the New Eng-
land States, New York, New Jersey, Pennsylvania, Delaware, Mary-
land, Virginia, and West Virginia, and the District of Columbia, in
none of which was it native except in the State first mentioned. At
that time it occupied also portions of Wyoming and southern
Dakota—where it was perhaps also native—and a considerable part
of the more arable portions of eastern Canada.

The farther spread of this insect, particularly southward, is of less
interest and has, in many instances at least, been dependent more or
less on the increased cultivation of the potato. The following addi-
tional statements as to the insect’s progress are taken from data

[Cir. 87]

5

collated mainly from the records of this office, some of which
are published more in detail by Tower. In 1877 the beetle ap-
peared in- North Carolina and Tennessee. The following year it
was reported to be completely overrunning portions of Canada,
being found eastward in New Brunswick. In 1879 it was recorded
from Manitoba. In 1880 its presence was observed in Texas. Since
about 1882 complaints of injuries have been made in Nova Scotia;
in 1885, at Savannah, Ga.; in 1888, at Jackson, Miss.; and in
Smith County, Tex. In 1892 the species had become abundant in
Alabama, and was noticed also in South Carolina. The following
year its occurrence was observed by H. G. Hubbard at Fort Assinni-
boine, Mont., which is evidently the most northern limit of its original
habitat, as it was not found there on potato. In sueceeding years
other localities were added in some of the States which have been
mentioned, but little of positive interest adding to its known dis-
tribution has been learned since 1893. It should be stated, however,
that the species has been found at Jacksonville, Fla.; in southern
Louisiana, and at San Antonio, Tex., but these extreme localities do
not indicate permanent location.

PRESENT DISTRIBUTION.

The natural spread of the potato beetle southward increases from
time to time, as evidenced by reports that reach this Department
yearly. Undoubtedly, however, the extreme northern and southern
territories which it invades do not become permanent habitats for the
insect, the species dying out, mainly because of extremes of cold in
the one case and of heat in the other, to be reintroduced in later years
when conditions favor its multiplication and spread from other
regions.

It has been calculated that it increased its range from its original
home to the Atlantic coast at an average annual rate of about 88
miles. Its spread eastward was accomplished largely by flight, as
the writer had occasion to observe when a resident of Cleveland in
the early days of its invasion of northern Ohio. Great numbers of
‘beetles were seen on bright days in spring and early summer, with
outspread wings, being carried directly eastward by the winds.

It has also been disseminated largely by railroads and by lake
vessels, and has thus been able, through the direct agency of man, to
cross the more barren plains bordering its native confines and the
barriers made by large bodies of water. So it will be seen that the
winds and waters and eastbound trains have all aided in its dis-
semination eastward. Riley, from whose works the present account
of the early distribution of the insect has been taken, observed the

aL. ¢, pp. 36-39.
[Cir: 87]

6

beetles on Lake Erie in 1870 on various floating objects, and the
writer in subsequent years saw the borders of the same lake lined for
a foot and more with the hordes of these beetles that had been blown
into the water and had then been cast up on the shore.

Beginning with about 1880, it will be noticed, the Colorado beetle
appeared in many potato fields of the Gulf region and elsewhere in
the South. In certain localities, particularly in Alabama (where it
was quite injurious for a time) and South Carolina, this insect seems
to have disappeared, and httle danger of continuous injury need be
anticipated there, as invasions of extreme Lower Austral territory
have thus far been merely sporadic appearances. Still, whenever
atmospheric conditions favor, the species does temporary damage in
such places, only to be killed down again for a number of years, after
which the beetles reappear, sometimes invading new localities. It
thus will be seen that it would be a somewhat difficult task to outline
definitely the permanent distribution of this insect. It is nearly
limited, however, as regards severe injuries to the country east of
the Rocky Mountains, extending from the Lower Austral to the
Transition life zone, and is likely any year to be injurious in extreme
portions of this area.

Injuries by this species in the potato section of Aroostook County
in northern Maine are well known, and the region there, as well as are
portions of Colorado, is credited to the Boreal life zone.*| From recent
reports it is fair to say that the species is scarcely a pest at the pres-
ent day in its original habitat nor in neighboring States, since during
the last five years no reports of extensive injuries have been received
from Colorado, Kansas,’ Nebraska, or South Dakota. It appears to
be firmly established, however, in the States just west of the Missis-
sippl River and from there eastward to Nova Scotia and New Bruns-
wick and southward to the northern portions of the Gulf States.

DISTRIBUTION LIMITED BY EXTREMES OF TEMPERATURE.

Some of the conditions which prevent the too rapid multiplication
and permanent establishment of the potato beetle are known. At St.
Louis, Mo., is was noticed by Riley that during very hot, dry weather,
as in 1868, this insect failed to go through its transformations in the
ground, the latter becoming so hot and baked that the pup dried
out, and the beetle, if it succeeded in throwing off the pupal skin,
failed to make its way to the surface. It was also noticed that the
larvee frequently perished under the broiling sun when the ther-

«These regions may in time be recognized as lying within the Transition zone.

6 Report from Mr. Warren Knaus, dated May 18, 1907, states that this insect
has appeared in great numbers in Kansas and threatens serious damage to young
crops.

[Cir. 87]

ie

mometer ranged near 100° F. During the intense heat that prevailed
during the summer of 1896 the writer noticed the same conditions in
and near the District of Columbia, the eggs and larve being literally
dried up on the potato plants, and, the species temporarily disap-
pearing altogether.

Northward the Colorado potato beetle is practically limited to
the Transition zone, although it occasionally invades the Boreal
zone, as, for example, in Colorado, where it has been found 8,000
or more feet above sea level. Severe winter weather alone probably
has little effect upon the insect, since it hibernates, as a rule, exclu-
sively in the beetle state and deep in the ground. It is, moreover,
one of our most hardy species, ranking with the hard-shelled snout-
beetles in its resistance to cold and frost. Cold snaps, however, over-
take the insect before it has sought out proper hibernating quarters,
and when these occur it is doubtless killed off in great numbers. As
was predicted years ago, the Rocky Mountains have proved an
impassable barrier for this species, and the insect has not been able to
reach the Pacific coast or neighboring States west of such barrier.

INJURIES, LIFE HISTORY, AND HABITS.
NATURE OF INJURY.

A few remarks in regard to the nature of the injury inflicted by
this insect are pertinent. Beetles and larve are destructive in nearly
equal proportions. In times of its early occurrence east of its origi-
nal limit this insect not only caused the entire loss of crops, but some-
times destroyed the potato yield of whole counties and of large por-
tions of some States. Indeed, at one time it materially affected the
market price of potatoes, not alone by reason of its direct depreda-
tions, but in discouraging farmers from the cultivation of the potato
on an extensive scale. Thus in 1873 the price per bushel at whole-
sale in the St. Louis market reached the high figure of $2. At the
present time, fortunately, every progressive grower recognizes the
fact that the control of this species is a part of the necessary routine
connected with the culture of this tuber.

It was early recognized that the depredations of this insect ma-
terially affected the quality of the tuber through the defoliation to
which the vines were subjected, and it was at one time difficult to
obtain potatoes that were not watery when cooked. This raises the
question whether the very marked decrease in quality of potatoes in
general at the present day is not due directly to the many years in
which the tubers have been deprived of due nourishment by more or
less defoliation of the plant itself; for, despite all the remedial
measures that are usually practiced, such as the liberal use of arsen-
icals and “ bugging” or jarring, a certain amount of injury nearly

[Cir. 87]

8

always takes place, which can not fail to affect the tubers when it has
oecurred practically without intermittence for periods of from twenty
to forty years.

FOOD PLANTS.

A wild species of Solanum (vostratum, and perhaps also cornutum)
is an original food plant of this potato beetle, and the latter is proba-
bly incapable of developing for any number of generations on plants
other than those of the potato or mghtshade family (Solanacez).
The genus Solanum is preferred, and the potato, because of its greater
succulence and less acrid taste, is now chosen in preference to plants
that grow wild. Still, the insect is nearly always found where its
wild food plants grow, particularly where poisons or repellents are
used in near-by gardens. It feeds on practically all solanaceous
plants, including eggplant, tomato, tobacco, ground cherry (Physa-
lis), thorn apple, and Jamestown weed (Datura), henbane (Hyoscya-
mus), belladonna, petunia, and pepper. The last is not often at-
tacked, nor are the other plants of different genera from the potato,
under ordinary circumstances. Occasionally, when none of these
are to be had, the insect will feed on certain weeds and garden plants,
among which are cabbage, thistle, and mullein.

It was long ago ascertained that the tender-leaved varieties of
potato are most affected, while other kinds, with less tender foliage,
such as Peach Blow and Early Rose, are comparatively immune, more
particularly when growing in the same field with the preferred
variety. Even eggplant seems to be preferred to certain varieties of
potato, and is consequently damaged at times, and tomatoes are sub-
ject to injury when the foliage of potato is not available.

GENERATIONS.

The normal number of generations of the Colorado potato beetle
is evidently two. In fact Tower” has observed that this number
in both temperate and tropical latitudes is a remarkably constant
generic character. In the course of his investigations he has not
been able to get the present species to breed more than twice in
a season without a period of hibernation or estivation. Person-
ally the writer has never observed more than two generations in
the District of Columbia. Years ago, however, Riley made the
positive statement that this species is three-brooded in Missouri,’ and
Lugger has made the same statement in regard to its development in
Minnesota. Dr. J. B. Smith claims two generations in New Jersey,

a Loe. cit., p. 243.
6 First Annual Report State Entomologist Missouri, 1869, p. 107.

[Cir. 87]

9

with sometimes a third partial generation which hibernates in the
pupal condition. Considering the faet that this species has invaded
new territory and does not live an entirely natural life, having an
abundance of food and not being restricted to its single normal plant,
it certainly seems possible that a third generation might be produced
in an exceptionally warm and humid season, and especially in the
most southern localities where it has become established.

LIFE HISTORY.

Hibernation takes place in the beetle stage, under the ground, some-
times to a considerable depth, the beetles having been unearthed from
a few inches to several feet beneath the surface. As a rule, however,
they do not penetrate deeper than 8 or 10 inches. Exceptionally the
beetles winter over in rubbish.

The beetles make their initial appearance quite early in spring, at
times issuing from their hibernating quarters soon after the first
thaw. Az this season they fly readily during the more heated por-
tions of the warmer days, and make aerial journeys of considerable
extent. “In flight, the striped elytra are raised and held motionless
from the thorax, while the gauzy wings, unfolded and vibrating,
strike pleasantly on the eye as the sun intensifies their rosy hues.”
These flights frequently take place before there are any potato plants
for the insect to feed upon, so that as soon as the leaves begin to push
their way through the ground the beetles are in readiness for the
feast. After a few days of feeding the females deposit their eggs.

The eggs are laid mostly on the under surface of the leaves, and
they hatch in from four days to a week or a httle later, according to
temperature. In from sixteen days to,three weeks the larve usually
attain maturity. They pass through four stages or instars,‘ then
descend into the earth and undergo transformation to pupz and sub-
sequently to beetles, in cells which the larve form for the purpose.
The minimum period of the pupal stage observed at Washington,
D. C., in August, 1906, in a very high temperature with correspond-
ing humidity, was seven days. This will be two weeks to a little
longer in a lower temperature. The insect is to be found in prac-
tically all stages, and particularly as beetles, during the summer
months or as long as any solanaceous plants are available as food,
Tt has been learned that the eggs continue developing in the ovaries
during a period of about thirty-five or forty days, and it is probable
that this species, in common with some others, has the ability of
retaining the eggs until a suitable place has been offered for their

“Observed by Messrs. A. A. Girault and A. H. Rosenfeld at Myrtle, Ga., in
May and June, 1906.

[Cir. 87]

10

deposition. A single female is said to be capable of producing from
five hundred to a thousand eggs. Five hundred and twenty-five were
observed by Girault and Rosenfeld in the case of one female, laid in
masses of from 9 to 53, from May 21 to June 5.

The entire life cycle from egg to adult may be passed in about four
weeks. The beetles of the last generation issue early in autumn, feed
for another three or four weeks, and then enter the earth for hiberna-
tion.

NATURAL ENEMIES.

It has already been stated that atmospheric conditions, with the
exception of extreme heat in its more southerly range, are not espe-
clally important factors in the repression of
this species; hence its fluctuation in num-
bers, which is noticeable at least locally
every season, must be accounted for by the
activity of its imsect enemies, the numbers
of which are legion. Several groups of these
enemies are known, each of which contains,
as a rule, many species. Among the most
important are
ladybirds,” many

Fic. 4.—A ladybird (Hippodamia ; b
convergens) Which preys on the COMMON Species ot
Colorado potato beetle. En-

larged (author’s illustration). which > 1 both

their larval and
adult stages, prey upon the potato beetle,
destroying great numbers of its eggs and
young larve. One of the commonest of
these ladybirds is illustrated for compari-
son with the Colorado beetle by figure 4. Fic. 6.—Lebia grandis, an impor-
Several ground-beetles,” also of predaceous Neen ie iad
habits, attack and devour the larve of this . a
potato beetle, and of these the so-called great Lebia (Lebia grandis
Hentz, fig. 5) is particularly attached to this species, following
it wherever it goes and doing perhaps more effective service than

any single natural enemy of which we have knowledge. Sev-
eral soldier-bugs also attack it, one of which, the spined soldier-

a'The ladybird enemies of this species are: Coccinella 9-notata Hbst., C. san-
guinea L., Megilla maculata DeG., Hippodamia convergens Guér., H. 15-punce-
tata L., H. glacialis Fab., Anatis 15-punctata Ol. (ocellata), and Chilocorus
bivulnerus Muls.

bCarabid enemies include the great Lebia (Lebia grandis Hentz), the fiery
ground beetle (Calosoma calidum Fab.), Pasimachus elongatus Lec., Harpalus
caliginosus Fab., Lebia atriventris Say, and Brachynus kansanus Lec.

[Cir. 87]

aah

bug,* is illustrated at figure 6. Other natural enemies are robber
flies,’ spiders, and a tachina fly. This last develops within the body
of the potato beetle larva and has been observed so abundant in
potato fields that its buzzing resembled the noise made by the swarm-
ing of bees. Wasps of some species attack the larvee, and the rust-
red social wasp? has been seen carrying them to provision its nest.
Not infrequently the beetle is found partly covered by dull, yellowish,
rounded mites. These are external parasites ° and help somewhat in
reducing their hosts. A species of daddy-long-legs is also a natural
enemy.!

Other predatory insects include a tiger beetle (Zetracha virginica
L.) and two rove-beetles (Philonthus apicalis Say and Quedius molo-
chinus Grav.). Most of the species listed above have been recorded
by Riley, but many have also been observed independently by others,
and correspondents
of this Bureau fre-
quently call atten-
tion to the com-
moner forms.

Thus far only in-
sect foes of the po-
tato beetle have
been discussed, but
certam mammals,
birds, amphibians
or batrachians, and
reptiles are well-
known enemies.

One of the most im-

portant of the birds "6. 6.—The spined soldier-bug (Podisus maculive ntris) : Adult at leit,
nymph at right. Much enlarged (original).

is the rose-breasted
grosbeak, whose services as an enemy of this beetle have been little
appreciated until comparatively recent times. The bobwhite or quail

«The soldier-bugs include Podisus maculiventris Say [spinosus], P. cynicus
Say, the bordered soldier-bug (Stiretrus anchorago Fab., Perillus cireumeinctus
Stal., P. claudus Say, Milyas cinctus Fab., and Sinea diadema Fab. These com-
monly attack the larval potato beetle. Nezara hilaris Say and Euschistus va-
riolarius Beauv. are said to have the same habit, but can not be important
enemies, as they are naturally herbivorous.

»b Proctacanthus milbertii Macq.

¢ Phorocera (Lydella) doryphore Riley.

d Polistes rubiginosus Lep. P. pallipes Lep. is said to have the same habit.

eThe most abundant of these is Uropoda americana Riley.

f Liobunum (Phalangium) dorsatum Say.

g This bird is one of the most important enemies of an equally destructive
species, the chinch bug. ;

TION es teh7ea |

12

also does excellent service and destroys many. Other birds which are
known to eat the potato beetle, on the authority of the Biological]
Survey, are the following: Ruffed grouse, nighthawk, cuckoo, scarlet
tanager, the wood, hermit, and olive-backed thrushes, and robin.
The crow not only picks beetles from the vines, but digs them from
the earth. The cardinal is a well-known potato-beetle destroyer, and
even the English sparrow has been seen to eat them.

Domestic fowls are of some assistance in destroying this pest, and
of these the duck early took to this insect, which is distasteful to some
other fowls. For some time after the spread of the Colorado beetle
to new territory chickens did not attack it, presumably because it has,
in common with many other leaf-beetles, a nauseous taste. For sev-
eral years, indeed, it was believed to be actually poisonous. After a
time, however, chickens became better acquainted with this insect
and began devouring its eggs and afterwards the larve, finally eating
the beetles with apparent relish. Skunks and snakes are reported to
eat the beetles, and toads frequently gorge on them.

cs

METHODS OF CONTROL.

This species is not a difficult one to control, no other method being
necessary for-its destruction than the free use of an arsenical or
mechanical means. Before taking up the remedies that may be most
profitably employed, it may be well to preface with the statement that
an arsenical liquid spray is preferred, and that dry arsenicals, hand-
picking, and jarring are practicable only on a small scale where the
grower has no spraying outfit, and occasionally when infestation is
sheht and limited toa small area. Every market gardener should be
equipped with a good spraying outfit.

MECHANICAL METHODS.

Jarring, if employed early in the season, is of considerable value.
It is a time-worn remedy and so well known as scarcely to need
description. It is customary in many localities to gather the beetles
and their larve in pans containing a little water on which a very
thin scum of kerosene is floating. Large shallow milk pans are excel-
lent for this purpose. At the same time the egg masses should be
picked where seen. Numerous apphances have been invented and
some patented for destroying this pest, but the arsenicals are so
effective that other remedies are really not necessary.

Brushing—The susceptibility of potato-beetle larvae to extreme
heat, as has already been recounted, indicates that a remedy much in
vogue against the asparagus beetle, namely, the mere brushing of the
larve from the plants on an extremely hot and dry day, will be effect-

[Cir. 87]

13

ive. So far as the writer knows, however, this has never been given
a thorough trial for the potato beetle. It should be tested.

Fall and spring plowing are of value in a general way, as for
other insects which pass the winter in the earth, but they are by
no means perfect measures, as the beetles are hardy and not much
affected by this treatment.

ARSENICALS,

Arsenicals are the best remedies for the Colorado potato beetle,
and on small potato patches Paris green is usually applied dry, mixed
with flour; but, as previously stated, it is best used as a spray.
Where early hand methods have been employed, thorough treatment
with an arsenical should follow.

Paris green, dry.—When applied dry, Paris green is mixed with
from 10 to 20 parts of cheap dry flour, sifted land plaster, or fresh
air-slaked lime. This remedy affords best results early in the sea-
son on young plants. It should be dusted on preferably when the '
dew is on and by means of powder guns or bellows, or the so-called
“ dust-spray ” machines, so as to cover the plants and leave as little
surface as possible for food for the first-appearing beetles. In spite
of this, however, some beetles will succeed in depositing their eggs on
the lower surface, which is difficult to reach with a dry mixture, and
when the larve hatch another application must be made. In fact this
remedy must be used for some time or until the plants obtain a fair
growth, when spraying will be found more effective.

The Paris green spray is prepared by mixing the arsenical with
water or Bordeaux mixture“ at the rate of 1 pound of poison to 75
to 125 gallons of the diluent. If water alone is used, quicklime
in about the same proportion as -the poison should be added to
prevent scorching. For the proper mixing and application of this
spray a bucket pump or knapsack sprayer of good quality is sufli-
cient for use in small gardens, but on a larger scale a potato sprayer
to be drawn by one or two horses through the rows of plants is
necessary. With the latter, from two to six rows can be treated at
2 time. Special four and six row potato sprayers are on the market.
The Paris green should be mixed with a small quantity of water into
a thin paste before the bulk of water is added and should then be
thoroughly blended by churning in the force pump or sprayer. The
mixture, being a mechanical one, is not constant, and the Paris green
will sink to the bottom. To avoid this it must be stirred constantly
while being applied. It is advisable to use the Bordeaux mixture as a
diluent. as this is a valuable insect repellent as well as a standard

a Directions for the preparation of this fungicide and the arsenicals here dis-
cussed are given in Farmers’ Bulletin 127, U. 8. Department of Agriculture,
which can be obtained on application to this office.

[Cir. 87]

14

fungicide, and it operates also against different forms of bight and
other diseases which may threaten the crop.

Arsenate of lead serves the same purpose as Paris green, and for
use against the Colorado potato beetle is still more valuable. Com-
plaints have been made that several applications of Paris green are
necessary during the season, and extra doses are required after each
rain. Arsenate of lead is applied in practically the same manner as
Paris green, but it contains less poisonous arsenical (60 to 70 per
cent when dry), and being sold usually in the form of a paste it
is used at a considerably greater strength—i. e., about 1 pound com-
bined with 15 to 25 gallons of water or Bordeaux mixture. Being
more adhesive, it adheres more firmly to the leafage and is much less
likely to produce scorching.“ Its adhesiveness is still more enhanced
by the addition of about the same amount, by weight, of resin fish-oil
soap as of the arsenical used.

The number of sprayings to be apphed will depend somewhat upon
local and seasonal conditions. Two or three will ordinarily suffice
for the spring brood, especially if apphed just after the eggs have
hatehed, and the same number should be apphed for the second
generation.

Other arsenicals may be used if preferred. Among these are ar-
senite of lime with soda, which has the merit of being as efficient as
Paris green and lime and far cheaper. It is not on sale at the present
time ready made, like arsenate of lead. Scheele’s green, similar to
Paris green, is employed in the same way as the latter.

Summary—To sum up the directions for the use of arsenicals, it
should be said that arsenate of lead, because it can be purchased
already combined, in paste form, which is preferable, takes first place,
in the writer’s opinion, as a potatd-beetle insecticide. The mixture of
Paris green, lime, and water is in nearly the same class, because the
ingredients can be purchased anywhere. The dry Paris green mixed
with air-slaked lime properly comes last, as it is less effective than
the other mixtures and much of the material is wasted.

Precautions to prevent poisoning.—In the use of arsenicals, as well
as other poisons, care should always be taken to avoid accident. This
‘an. be best accomplished by plainly marking the contents on all
receptacles, such as bottles or packages, in which the poison is kept.
In addition a “ POISON ” label, which can be obtained of any drug-
gist, should be affixed. It is best also to keep such substances under
lock and key. The utensils employed in the preparation of the mix-
tures which have been discussed should be thoroughly cleaned after
use.

“Jn point of fact it can be used at the rate of 1 pound to 10 gallons without
injury, but this proportion is not advisable, owing to the extra cost, and scorch-
ing would be apt to follow its use on plants exposed to hot sunlight.

[Cir. 87]

15
ERADICATION OF WEEDS AND COOPERATION.

It is always wisdom on the part of the agriculturist to keep down
the weeds on the farm, and in the treatment of the present insect if
those weeds which are known to furnish it with food, such as sand-
bur and Jamestown weed, were cut just before seeding, it would pre-
vent the overdevelopment of the pest and of other insects which feed
on the weeds, as well as the weeds themselves. The farmer should
familiarize himself with the wild food plants of this pest.

Keeping the potato patch and, in fact, the entire farm as free as
possible from solanaceous weeds should be practiced by all farmers of
a neighborhood, and if the potato grower could secure the cooperation
of his neighbors in the use of an arsenical spray, and would also de-
stroy the insects by spraying infested wild food plants, the effect
would soon be noticeable, as there can be no doubt that the species
would soon be reduced to small numbers, at least in limited areas, if
this cooperation were thorough and persistent. This statement is
based on the fact that the beetles are seldom if ever seen migrating
nowadays in any such numbers as in earlier years, and there is not
therefore the constant danger of reinfestation from a distance as was
formerly the case. There may, of course, be occasional exceptions.

Finally, as a general proposition, the potato grower should keep
his potatoes free from diseases, such as wilt and scab, and spray
for flea-beetles and any other insects which may be found in addition
to the Colorado beetle. He should also pay particular attention to
the methods of growing best adapted for his location. Information
in regard to the methods of potato culture is furnished in Farmers’
Bulletin No. 35, U. S. Department of Agriculture, and potato dis-
eases and their treatment are considered in Farmers’ Bulletin No, 91.
Both of these publications can be had on application to the Secretary
of Agriculture.

Approved:

JAMES WILSON,
Secretary of Agriculture.

Wasuinerton, D.C., April 10, 1907.

[Cir. 87]

O

SMITHSONIAN INSTITUTION LIBRARIES