= ne

SB

818
C578 lo. 73.
ENT uited States Department of Agriculture,

the females, in the oper-

BUREAU OF ENTOMOLOGY,

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

THE PLUM CURCULi0O.
(Conotrachelus nenuphar YWerbst. )
By Frep JOHNSON and A. A. GIRAULT,

Engaged in DPeciduous-Fruit Insect Investigations.
INTRODUCTION.

The small, crescent-shaped punctures so commonly found on plums
and other stone fruits in orchards east of the Rocky Mountains are
made by a small snout-beetle of rough sculpture, known as the plum
curculio. These beetles issue from their winter quarters about the
time the trees are in
bloom, and feed on. the
tender foliage, buds, and
blossoms. Later they
attack the newly set
fruit, cutting small cir-
cular holes through the
skin in feeding, while

ation of egg laying,

make the crescentic cuts

ae characteristic of this Fic. 1.—The plum curculio (Conotrachelus nenuphar): a, larva;
species. The egg, de- b, adult; c, pupa. Much enlarged (hair line to right of b
posited under the skin indicates natural length of adult). (From Chittenden.)
of the fruit, soon hatches into a very small whitish larva or grub,
which makes its way into the flesh of the fruit. Here it feeds greedily
and grows rapidly, becoming, in the course of a fortnight, the fat,
dirty white “ worm ” so well known among fruit growers.

The plum curculio is a native of North America and for more than
one hundred and fifty years has been known as an enemy of stone
fruits. Our early horticultural literature abounds with references to
its depredations. In more recent times the great increase in plantings
of fruits, brought about to supply the increased demand, has per-
mitted it to become much more abundant than formerly, and the plum
curculio constitutes, at the present time, one of the most serious
insect enemies of orchard crops.

This species is quite generally distributed over the United States east-
ward of about the one hundredth meridian, its range extending from
southern Canada to Florida and Texas. Westward of the States

28804—No. 73—07

bordering the Mississippi River it rapidly loses its importance as
2 pest, owing probably to the more arid condition of the climate.

LIFE HISTORY AND HABITS.

Like other beetles, the plum curculio has four distinct stages in its
life, namely, the egg, the larva or “ worm,” the pupa, and the adult or
beetle. The last three stages are shown much enlarged in figure 1.

The insect passes the winter in the adult or beetle stage under aceu-
mulations of partly decayed leaves, among the closely packed dried
erass of sod-covered orchards, and probably wherever suitable protec-
tion from the weather may be found. As its depredations are usually
the worst in those portions of orchards which are in close proximity
to woods, the beetles doubtless find the natural accumulations of rub-
bish in such situations very suitable places in which to pass the winter,

In Niagara County, N. Y., during the
= fall of 1905, numerous careful searches for
~ beetles were made under leaves and rubbish
in plum, peach, and apple orchards, and
woodlots and hedgerows adjoining them.
These searches did not discover any hiber-
nating beetles except 1n one large apple or-
chard where the ground was covered with
sod. Failure to find beetles in other places
was probably due to the scarcity of the in-
sect in plum and peach orchards durmeg the
preceding summer. In the sod-covered
apple orchard mentioned, a total of 42
beetles was found at various times between
October 14 and November 28. In every
vase they were beneath partly decayed
Fig. 2.—The plum cureulio: Adult’ leaves under apple trees and often in de-

female on plum, showing the cir- NG : “7: :

cular feeding punctures and the DPYessions in the soil into which the leaves

crescentie egg-laying punctures. were closely packed.

hag LN In the spring, when the fruit buds are
unfolding, the beeties begin to emerge from their winter quarters
and feed to some extent on the blossoms and tender leaves. Mating
soon begins, and by the time the fruit is well set the beetles make this
fruit the chief object of their attention. Figure 2 is an enlarged
illustration of a young plum, showing a female beetle and the char-
acteristic feeding and egg-laying punctures which she has been
engaged, with others, in making. The circular punctures are made
in feeding; the others are eg@ punctures.

A single egg is deposited in a puncture, although several may be
placed in a single fruit. From one to eight eggs may be deposited

daily by an individual female. Oviposition and feeding continue
[Cir. 73]

3

for several weeks and in the case of the hardier individuals may
extend over a period of several months. Egg laying is, however,
most active during the first four or five weeks after emergence of the
beetles in spring.

During recent years egg-laying records for the season, made in
widely separated localities, show that the total number of eggs depos-
ited by the female varies widely. In Maryland Professor Quain-
tance and Mr. R. I. Smith found that the number deposited in plums
by females of longest life varied from 276 to 436. At Washington,
D. C., the junior author during the past season obtained records of
oviposition in plums which showed a range of from 273 to 560. A
record of egg deposition in plums was also made by the senior author
in westetn New York during the same season, and this showed a
range of from 76 to 254. Professor Crandall, in Illinois, obtained
records for apples showing a range of from 18 to 252 for individuals
of longest life. The number of days required for the eggs to hatch
varies according to temperature. Records of the past season show
that at Washington, D. C., the time varies from about three to five
days, whereas in western New York it varies from about four to
seven days.

When the larva attains full growth, which requires some twelve
to eighteen days, it bores its way out of the fruit and enters the soil.
At a depth varying from one-half inch to 2 inches, rarely much
deeper, it forms an earthen cell in which to pupate. The time
required for the pupal stage and the emergence of the normally
colored beetle is from three to four weeks. Thus the period of devel-
opment from egg to adult is covered in from about five to seven
weeks. Differences in weather and soil conditions, however, cause
the time of emergence of the adults to vary greatly. When the soil
is very dry, the beetles may remain in the pupal cell for days or even
weeks after their normal period of emergence, whereas after a heavy
rain they may emerge in numbers. Thus a new generation of beetles
from eggs deposited early in the season appears some time before all
the parent beetles have died. In fact, some of the overwintering bee-
tles have been kept alive until late in October. ;

Upon emergence from the soil, beetles of the new generation almost
immediately turn their attention to ungathered fruit, if this be pres-
ent on the trees. In Georgia peach orchards, as observed by Mr. J. H.
Beattie, of this Bureau, the beetles attack the foliage in cases where
the fruit has been harvested. Prunes, plums, and peaches often suf-
fer severely, and the injury is familiar to many orchardists as the
circular punctures and pits made at the stem end of the fruits, caus-
ing the latter to rot and drop off a few days before ripening. The
work of the new generation of the curculio is conspicuous on late
varieties of apples also, the beetles feeding upon these until the

[Cir. 73]

4

approach of cold weather, when they leave the trees and seek winter
quarters. In orchards where sod and other conditions permit the
accumulation of leaves and rubbish directly beneath the trees many
beetles simply go to the ground, work beneath the leaves, and there
pass the winter, and are thus near at hand to attack the fruit when
it develops the following spring.

FOOD PLANTS.

The natural food plant of the plum curculio is undoubtedly the
native wild plum. The curculio also feeds upon and breeds in wild
erabapples, wild cherries, and haws, and is reported to breed in the
persimmon. It has also been bred from a common fungous growth of
plums and cherries called “ black-knot” (Plowrightia morbosa
Sace.), though this is evidently an abnormal habit. Of the culti-
vated pome and stone fruits, nearly all are attacked for feeding and
egg-laying purposes, including plums, peaches, cherries, nectarines.
apricots, apples, and pears, but of those listed the smcoth-skinned
sorts, notably plums, are preferred. The beetle feeds also upon the
blossoms and folage of its various food
plants, but to a much more limited
extent.

CHARACTER OF INJURY.

The plum curculio is injurious in both
the larval and adult stages, though it is
in the adult stage that it is most harm-
ful. The young fruit becomes badly
scarred by the more or less crescentic

Ff tides OW aN ege punctures and pit-like feeding
Sue ures, and in late summer and! tall
\ a punctures, and in late summer and fa

er
fruit is injured by the feeding of beetles

Fic. 3.—Nearly full-grown larva of the
plum curculio in a ripe peach, show- of the new generation. The presence of

coe ee mi the larva in the young fruit generally

causes it to fall, and in cherries and
nearly ripe peaches and plums in which it may develop the fruit is
spoiled. (See figure 3, showing injury of this character to a ripe
peach.) ‘The character of injury varies somewhat according to the
kind of fruit, and for this reason is best discussed under separate
headings.

Plum.—The plum is undoubtedly the favorite food of this inseet
and accordingly suffers severe injury when the curculio is abundant.
Kees are deposited in the young fruit, and this may soon fall to the
ground, a result of injury caused by the young larve. In seasons of
short crops very little fruit may remain to ripen. With varieties
which are inclined to overbear in seasons of very heavy crops, how-

ever, this kind of work may result in much good by thinning the
[Cir. 73]

4)

crop. As the fruit beeomes larger the many egg and feeding punc-
tures which it has received cause it to become misshapen and to exude
masses of gum. When the plums become of some size and are grow-
ing rapidly, the larve are apparently not able to develop, but when
the fruit is nearly mature and softer they are_better able to survive,
and thus ripe fruit on the trees is often “ wormy.” In certain locali-
ties late varieties are sometimes badly injured by feeding punctures
of the new generation of adults.

Apple—Curculio injury to the apple has lately been the cause of
considerable complaint. It is much like that done to the plum,
though the young fruit is not so likely to fall to the ground when
punctured, and the larve are probably never able to mature in fruit
which remains on the tree. The young fruit may largely outgrow
the eg@ puncture, which may show in the ripe fruit as a brown and
roughened, more or less crescentic spot which does not materially
affect its value; but when badly punctured, especially by feeding of
the beetles, the fruit as it grows becomes knotted and pitted. Fall
and winter varieties may be seriously injured by the feeding upon
the fruit of beetles of the new generation.

Peach.—On account of the thick fuzzy pubescence on the young
peach, this fruit is perhaps attacked less early than is the plum, but
the character of the injury is essentially the same. Many fall to the
ground. Those remaining on the trees, if badly punctured, become
knotty and misshapen and often exude masses of gum from the
wounds. Such fruit will usually ripen prematurely. Ripe fruit
which appears perfectly sound, but which contains nearly full-grown
larve, is often found on the trees. To all appearances such fruit is
in first-class condition and is thus often shipped to market.

Cheriy.—In most cases infested cherries do not fall to the ground,
the larve maturing in the fruit on the trees. Usually but a single
larva is found in a fruit, and infestation is apt to go undetected.

Apricot and nectarine.—These are usually injured in much the same
way as are plum and peach. Isolated trees loaded with apricots are
often so badly infested that not a single fruit escapes.

Pear.—Curculio larve are apparently not able to develop in fruit
on the trees, hence injury is confined to the egg and feeding punctures
made by the adults when the pears are small. In fruit which does
not fall the injury may be quite outgrown, but in cases of excessive
puncturing the fruit is badly warped. .

NATURAL ENEMIES. .

Under the head of natural enemies are to be mentioned several
parasites of the plum curculio which play a very important role in
holding the insect in check. Perhaps the most important of these is
a minute hymenopterous insect belonging to the family Mymaride,

(Cir. 73]

6

which attacks the egg, although the latter is apparently well pro-
tected under the skin of the fruit. This insect is known by the scien-
tific name Anaphes conotracheli Girault. It is now known to occur
in Georgia, North Carolina, Virginia, Maryland, the District of Co-
lumbia, Kentucky, Connecticut, Texas, and Indian Territory, and is
apparently quite abundant. According to the few observations which
have thus far been made, it destroys in Maryland from 16 to 70 per
cent of the eggs, and as the life cycle in June was only nine days,
several generations of this parasite must successfully develop in the
egos of the plum curculio, thus increasing its efficiency.

The other parasites attack the larva or grub. They are Sigalphus
curculionis Fitch and its variety rufus Riley, and Thersilochus cono-

M. - Pars
Ba

Mya IND UY
oN
\ \ ALE a AU AN

S—. ——o

|< ma

Fria. 4.—Jarring for the plum curculio in a Georgia peach orchard. (Original.)

tracheli Riley. The former is of much more importance than the
latter because of its greater abundance. It is a common parasite of
several other coleopterous larve and is quite widely distributed.
Limited observations indicate that this parasite destroys about 20 per
cent of the larvee of the plum curculio. Thersilochus conotracheli has
not been met with outside of New York State, and the influence it
exerts in keeping down the curculio is perhaps very small.

desides the true parasites several predaceous beetles and ants attack
and destroy the curculio larve as they leave the fruit to enter the soil
for pupation. Their value in most cases does not equal that of the
parasites.

[Cir. 73]

Chickens are said to help greatly in destroying the beetles, espe-
cially in small orchards planted near the home.

PREVENTIVE MEASURES.

Although many methods have been proposed for lessening the in-
jury of this pernicious pest, only a few have proved of real value.

Jarring—Among these, jarring is the method which is perhaps in
most general use in protecting plums and peaches, and by many
orchardists it is believed to give the best results. Early observations
upon the plum curculio showed that this insect has a habit of falling
to the ground and “ playing possum” when disturbed. A knowl-

Fig. 5.—-The cart catcher in use in jarring for the plum curculio. (After Slingerland.)

edge of this habit has led to the capture of the beetles on sheets held
or spread beneath the trees, the trees being jarred by a sudden, for-
cible blow struck with a padded pole or mallet in order to dislodge
the beetles.

In the spring, about the time the calyx or “ shuck ” is beginning to
slip off from the newly set fruit, jarring is commenced and is con-
tinued daily or as often as the weather will permit for a period of
four or five weeks or until the operation ceases to yield many beetles.
Jarring is best done in the early morning or late evening, for at these
times the beetles are less active, drop more readily, and are not so
likely to escape by flying or crawling from the sheets as they are at
midday.

[Cir. 73]

8

There are several kinds of catchers in common use by orchardists.
One form is shown in figure 4+ and consists of a light framework 12
feet long by 6 feet wide, over which a canvas is stretched. The jar-
ring gang consists of five persons. Two of the frames of the dimen-
sions given are used together, each frame being carried by a couple
of women or boys, as shown in the figure. One frame is held on each
side of the tree, while the fifth member of the gang, who carries a
iong-handled padded pole, gives the trunk of the tree a sharp,
forcible blow. With this outfit a large number of trees may be
jarred in a very short time. It is therefore especially suitable for
work on a large scale. The curculios which fall to the sheets are
collected and destroyed when the end of the row is reached, and the
beneficial insects, principally ladybirds, are allowed to escape.
Where jarring on a smaller scale is desired, sheets can be made of a
size to be easily handled by one man. For this purpose frames 9 feet
by 44 feet are convenient and will answer for moderately sized peach,
plum, and cherry trees.

Another catcher which is in common use, especially by the plum
erowers of western New York (see figure 5), is a two-wheeled cart
upon which is mounted a canvas covering arranged in the form of an
inverted umbrella. There is a narrow opening at the front to receive
the trunk of the tree. When the catcher is in position, the trunk of
the tree is given a sharp blow. This causes the beetles to drop to the
canvas, from which they are swept into the tin receptacle, or “ hop-
per.” hanging under the center of the cart directly beneath an opening
in the canvas. Some operators place kerosene in the “ hopper” to
destroy the insects as soon as they fall into it. Others have chestnut
roasters placed at the end of the rows, in which the insects and rubbish
collected in the “ hopper ” are finally roasted.

Although the operations just described are somewhat laborious and
expensive, many orchardists have demonstrated that the outlay in
time and money thus invested will bring profitable returns. Some
interesting figures concerning the cost of and results from this work
as practiced in a Georgia orchard were obtained by Messrs. W. M.
Scott and W. F. Fiske during the season of 1900 and: published in
3ulletin No. 31, new series, of this Bureau. Some 200,000 bearing
peach and 50,000 bearing plum trees were jarred about 16 times
during the period from April 18 to June 1. Eleven gangs, or 55
hands, with 5 attendants, were engaged in the work. The total cost
for labor and repairs was placed at about $1,000. The number of
curcuhos caught during the season was estimated at about 137,000.
On the assumption that one-half of these were females, each capable
of laying 200 eggs, it will be seen that 13,700,000 eggs, less those
deposited by the beetles before capture, were kept from the fruit.

The amount of curculio damage in this orchard for the season was
[Cir 73

9

placed at about 4 per cent of the crop. In an adjacent orchard of
130,000 peach trees not jarred curculio injury was placed at 40 per
cent of the crop.

Poisons.—It has long been known that the beetles feed on the plants
upon which they lay their eggs, and numerous careful experiments
have shown that they may be poisoned by thoroughly spraying the
trees with arsenicals. The results of such work, however, appear to
vary somewhat, depending on the relative abundance of the beetles
during a given season. Many orchardists have adopted the practice
of spraying for the curculio in preference to jarring, on account of the
labor involved in the latter and the frequency with which the work
must be repeated to make it effective. Professor Crandall, in Uh-
nois,¢ has shown that curculio injury to apples may be reduced some
20 to 40 per cent by a reasonable number of poison applications. The
results of persistent spraying by orchardists in western New York
are set forth by Professor Slingerland in Bulletin No. 235 of the Cor-
nell Experiment Station. It is there stated that the growers are
almost all in favor of spraying for the curculio, especially upon plums
and cherries. The exact value of arsenicals in controlling the cur-
culio on peach has apparently not yet been determined, though there
are numerous growers who spray their peach trees every year and
report good results. The foliage of peach is lkely to be injured,
however, by repeated applications of arsenical sprays, and the grower
using these sprays for the first time should proceed with caution. In
localities where it has been established that no injury results from their
use, they are to be recommended. Other stone fruits, while Hable to
foliage injury from repeated applications of arsenicals, are appar-
ently not so sensitive as is the peach, but care should be taken at all
times that the poison be used as recommended below. Apple and
pear are rarely, if ever, injured by the proper use of arsenicals. Of
the poisons available, such as Paris green, “ green arsenoid,” and
arsenate of lead, the latter is least likely to be injurious and should
be used where stone fruits are to be treated. Liability to injury from
arsenical poisons will be greatly reduced by adding to each 50 gallons
of the spray the milk of lime made by slacking 2 or 3 pounds of good
stone lime. Where Bordeaux mixture is employed against scab and
other fungous diseases, the arsenical may be used in the fungicide,
and the milk of lime is then unnecessary. To be reasonably effective
in killing the beetles, arsenate of lead should be used at the rate of 2
pounds to 50 gallons of water. Paris green or green arsenoid should
not, on stone fruits, be used stronger than 1 pound to 150 or 200 gal-
lons of water. On pome fruits a somewhat greater strength may be
used without danger of injury to the foliage.

a Bul. 98, Ul. Agric. Hxp. Sta., p. 553.
[Cir. 73] ba

10

Since the period of feeding and egg laying of the curculio extends
over several weeks from its emergence in spring, several applications of
poison are necessary. The first application should be made as soon as
the blossoms have fallen, and three or four subsequent applications
should be made at intervals of eight to ten days. In the case of apple
the usual two applications for the codling moth or canker-worms—just
after petals fall and again within a week or ten days—will answer for
the first two applications against the curculio. In spraying for the cur-
culio, too much stress can not be laid on the importance of making the
applications as thorough as possible. The effort should be made to
cover every leaf, twig, and fruit.

Cultivation.—Another vulnerable period in the life of the insect is
that when the larva has reached its growth and has passed into the soil.
At a distance varying from one-half to 2 inches from the surface the
larva makes a small earthen cell in which to undergo its transforma-
tion to the pupa, and, later, to the adult beetle. While these changes
are taking place the insect is in a perfectly helpless condition, and the
stirring of the soil with a cultivator at this period will doubtless
break up the cells, causing the death of many of the delicate pupe.
Since cultivation is a necessary feature of orchard practice, effort
should be made to carry on a part of it at a period when a majority
of the insects are easily destroyed. Careful observations show that in
the vicinity of Washington, D. C., and southward the larve begin to
enter the soil about six weeks from the time fruit trees are in full
bloom. In Illinois, according to Professor Crandall, about two
months elapse between the period of full bloom and the date at which
larvee begin to enter the soil. Since the period of maximum egg lay-
ing covers from four to five weeks, there is a like period when the
pupee are in the soil in maximum numbers. Cultivations to destroy
the curculo should therefore begin six or eight weeks, according to
latitude, from the time of full bloom of the trees and should be con-
tinued for four or five weeks. Such work could be readily arranged
for as part of the regular cultivation given the orchard.

Gathering fallen firwit.—The number of curculios can be greatly
reduced by picking up and destroying the fallen fruit infested with
larve. Much of the infested fruit falls to the ground several days
before the larva is full grown and ready to leave it. If this be gath-
ered and burned, at intervals of three or four days, it will result in
greatly lessening the number of beetles to attack the fruit in the fall
and following spring.

Approved:

JAMES WiLson,
Secretary of Agriculture.

Wasuineron, D. C., April 14, 1906.

[Cir. 73]

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01272 7384