STATE PLANT BOARD
April 1944 1-616
UNITED STATES DEPARTMENT OF AGRICULTURE
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
NOTES ON THE LIFE HISTORY AND OTHER FACTORS AFFECTING
CONTROL OF THE GRAPE LEAF FOLDER
By Dwight F. Barnes, Division of Fruit Insect Investigations i
Life History and habits
Timing of insecticide applications
./ Acknowledgement is made to the following associates
for assistance in making and recording observations: Charles K.
Fisher of the Dried Fruit Insect Laboratory; George H. Kaloostian,
Oscar G. Bacon, Dennis F. Hallowell Jr., and Charles H. Quibell,
formerly connected with the laboratory; and Eugene M. Stafford of
the University of California.
The grape leaf folder (Desmia funerals (Hbn.)), one of the
secondary grape pests of the country, frequently causes.damage in the
California grape-growing areas, particularly in the San Joaquin Valley.
An infested area in Fresno County, varying in size from year to year,
has persisted for mere than 10 years. A survey made in the fall of
1945 showed that there was an area of about 150 square miles in which
spots of heavy damage might be expected in 1944.
Severe infestation causes defoliation which exposes the fruit
to the direct heat of the sun and reduces vine efficiency. Break-down
of the fruit follows entrance of mold and souring organisms through
feeding wounds made by the larvae on the ripening fruit.
The accepted methods of control are spraying with lead arse-
nate and dusting with arsenical or cryolite dusts, but knowledge of the
best time to make applications is indefinite. Treatments applied too
late in the development of a brood to be fully effective have been
common, and instances are known where, in a mistaken effort to save
late-maturing fruit, applications of insecticides were made after the
feeding for the season had been completed. Life-history studies at the
laboratory and field biology studies have been carried on at the Dried
Fruit Insect Laboratory, Fresno, Calif., to improve the basis for de-
termining the correct time for treatment.
LIFE HISTORY AND HABITS
The life history of the moth consists of four stages-egg,
larva. pupa, and adult. Information on the habits of the larval, or
feeding, stage and the adult, or egg-laying, stage is the basis for
understanding when treatments can be applied to the best advantage.
The moths begin to fly at the end of evening twilight each
day, and, on warm nights at least, flight continues all night. During
the day the moths rest in protected places in and around the vineyards.
A few, which have been disturbed while resting, may be seen in flight
There are normally three clear-cut broods of the grape leaf
folder each season in the San Joaquin Valley, shown in the accompany-
ing graphic records (fig. 1) for 4 years of trapping with malt-sirup
traps. A very small partial fourth brood occurs, but it develops so
late that food is not available for the offspring. Two instances of
hibernation of second-brood pupae have been observed. Winter is
passed in leaf envelopes in leaf debris on the ground in the vineyards.
In the spring, emergence of first-brood adults begins after vine growth
starts and continues until blossoming is well advanced. Trapping with
malt-sirup traps has shown that the average first-brood flight period
is 53 days, from about April 2 to Mey 24.
The females of the first brood lay their small, flat, iri-
descent eggs on the more mature leaves and on the surface of water
sprouts, or "suckers", on parts of the vines protected from cool winds.
On varieties trained on wires, as the Zante (Corinthe Noir) or Ribier
(Alphonse Lavallee), most of the first-brood eggs are found in the
heaviest foliage and usually on the south side. On varieties not
trained on wires, as the Muscat (Muscat of Alexandria), most of the
eggs are found low on the southeast side, where the females have been
sheltered from the prevailing winds. Pubescent (downy or hairy) sur-
faces are avoided by the females when depositing their eggs, and the
eggs are found on the upper surface when the lower one is pubescent,
or on either surface when pubescence is sparse. Although they may be
scattered anywhere on a leaf surface, a high percentage are placed in
the angles between the veins and the surface* Eggs are also concenr-
trated on the water sprouts, or "suckers", which start from the vine
trunks. A heavy egg deposit has never been observed on young vines or
vines without dense foliage to give protection from the wind.
During April and May eggs hatch in from 10 to 17 days, the
time decreasing as the season advances. The larval stage occupies 5
to 4 weeks and the pupal stage 10 days to 2 weeks. The entire develop-
ment, from egg to adult, requires from 6 1/2 to 7 1/2 weeks.
The young larvae feed in groups, eating the surface of leaves
which they have webbed together. Easily recognized areas where the
leaf surface has been removed between the webbed-together leaves are
found following this type of feeding. After about 2 weeks of group
feeding, the larvae separate and feed by eating the free edges of leaves
inside of pencil-sized rolls which they make at the leaf margins. At
least two rolls are made and occupied before the larvae are full-grown.
Full-grown larvae usually leave the rolls and make leaf envelopes in
which to pupate and transform to adults. The envelopes are small
sections of leaves partially cut away, folded, and tightly webbed to-
gether from within. Some of the larvae neglect. to make envelopes but
pupate within the feeding rolls.
Adults of the second brood emerge from mid-June to mid-July.
The average flight period is 29 days, from about June 17 to July 15.
The eggs laid by this brood are deposited almost exclusively on leaves
rolled by the first brood of larvae. Hatching occurs after 4 or 5 days,
larvae are full-grown in 2 to 5 weeks, and the pupal period lasts 7 to
11 days. The entire development, from laying of the eggs to emergence
of the adults, requires 4 to 5 weeks. The young larvae of the second
brood, as do those of the first brood, feed in groups, but many enter old
rolls instead of feeding between webbed leaves. Utilization of the rolled
leaves for egg laying and of old rolls for feeding brings about a concen-
tration of the second brood of larvae in the part of the vine occupied by
the first brood. Dispersion upward and outward on the vine occurs when
new rolls are made. By thetime the brood is complete the rolls may be
scattered over the foliage-of the vine.
Third-brood adults emerge from early in August to early in Sep-
tember. The average flight period is 54 days, from about August 3 to
September 5. This brood also utilizes the leaves rolled by previous broods
for egg laying and feeding. Dispersion and foliage damage by this brood
spread over the vine from the points reached by the second brood.
'-lggs laid by the third brood of moths hatch in 4 or 5 days, and
larvae '. e full-grown in 5 to 5 weeks after hatching. Only a few adults
emerge in the fall, consequently most of the brood spends between 6 and 8
months as overwintering pupae. A though the partially-cut-away pupe-al
leaf envelopes made by larvae of the first two broods remain attached to
the leaves on the vines, those of the third brood break from the dried
leaves and are found with their enclosed pupae scattered among the leaf
debris on the ground. Not all third-brood larvae pupate on the foliage,
for in heavy infestations some larvae leave the foliage or fruit on which
they have developed and overwintering pupae may be found under the loose
bark of the vine trunks.
The behavior of the females in seeking protection in the spring
influences not only the location of the infestation on individual vines
but to some extent in the vineyard. It is noticeable that, early in the
season at least, infestation is heavy near weedy ditch banks, shrubbery,
citrus trees, and other protected sites which the adults occupy while
resting during the daylight hours.
The larvae pass through 5 instars, or stadia, before pupation,
molting or shedding their skin at the end of each stadium. No character-
istic marks for field identification appear on the first two instars.
On the third a small black spot appears on each side of the body above
the second pair of legs, on the middle segment of the thorax, which is
the division of the body just behind the head. On the fourth instar
there are two spots, the second being indistinct early in the stadium.
In addition to three distinct markings on the thorax of the fifth instar,
a distinct spot appears near the anal end. As soon as feeding begins,
the ingested food showing through the translucent body walls gives the
larva a bright-green colors At the end of each stadium feeding stops,
food material is evacuated, and the color is lost by the time the larva
is ready to molt. Color reappears when the larva resumes feeding after
Making the leaf roll is an engineering feat of interest. The
larva, spinning a filament of silk, establishes an anchorage near the mar-
gin of a leaf and then reaches a short distance toward the middle of the
leaf to establish a second anchorage. It completes the strand by moving
the head back and forth 200 to 500 times, spinning and anchoring a thread
at each movement. Several strands made along the margin start the leaf
edge rolling as the strands dry and contract. Additional strands, which
slacken the previous ones, are required to complete a tight tube, open at
each end. Several rolls frequently are made on a single leaf.
Observations on the areas of leaf surface eaten during the de-
velopment of 69 larvae fed on Emperor grape foliage showed that the aver-
age was 5.54 square inches. The areas eaten by each larva ranged from
2.21 to 4.66 square inches. Less than 15 percent of the total was eaten
during the first three stadia, the period when the small larvae feed in
groups. The average areas eaten by each instar are assembled below.
AREAS OF FOLIAGE EATEN DURING LARVAL DEVELOPMENT
Average area eaten by each instar
1st 2nd 5rd 4th 5th Total
Square inches 0.02 0.06 0.59 0.75 2.14 5.54
Percent of total 0.6 1.6 11.7 21.8 64.1 100.
TIMING OF INSECTICIDE APPLICATIONS
The insecticides commonly used in the San Joaquin Valley for
the control of the grape leaf folder are lead arsenate sprays, usually
with wettable sulfur, or lead arsenate and cryolite dusts. Four to 6
pounds of lead arsenate and 5 or 6 pounds of wettable sulfur per 100
gallons are used in the sprays, while the dusts contain 40 to 50 percent
of the active ingredient, with hydrated lime or dusting sulfur as a
diluent, usually dusting sulfur.
The best period for making insecticide applications varies with
the different broods. In the first brood it lasts about 5 weeks, be-
ginning when 60 to 80 percent of the eggs observed on any day have hatched
and ending before 20 percent of the larvae seen on any day have begun mak-
ing their own rolls. This is the period between the start of bloom in the
early varietieE of grapes and the end of bloom in the late varieties; for
example, from the start of blossoming of the Zante to its end in the Mus-
cat vineyards. The delay of a month between the start of flight activity
and treatment is caused by the long period during which egg-laying females.
are present, the long incubation of the eggs during the cool weather of
early summer, and the slow development of foliage. If the treatment is
made too early, the steady increase in the area of new foliage will leave
much of the vine unprotected by poison and the larvae may roll and eat
The periods of insecticide application for the second and third
broods last about 2 weeks. They begin with the peaks of adult activity,
at which time more than 20 percent of the eggs observed on any day have
hatched, and end before more than 20 percent of the larvae seen on any
day have --de their own rolls. In the case of the second brood the
period falis in July, between the harvest of Early Elberta and Hale
peaches, while for the third brood it occurs after mid-August, between
the start and height of picking of Thompson Seedless (Sultanina) grapes
Since in the San Joaquin Valley grape-growing areas most ranch
homes are surrounded by vineyards, a simple method for securing informa-
tion about moth activity is to make nightly observations on the number
of moths collecting on the screens of lighted porches, recording the
numbers appearing on the same area at the same time after sunset each
night. Malt-sirup traps give information on activity during flight but
are impractical as indicators of the time for insecticide applications,
except where a group of grape growers might be willing to cooperate in
securing information for a district.
After flight activity starts, weekly or semiweekly counts of
eggs and larvae on infested leaves will serve as guides for determining
when to put on dusts or sprays. The number of eggs and the number of
larvae in each stage should be recorded. When the examinations of first-
brood eggs show hatching of about 80 percent of the eggs observed on any
day, the time to begin treatment is indicated. For the later broods the
figure is about 20 percent. When more than 20 percent of the larvae seen
on any day bear more than one spot (fourth instar) the end of the period
is indicated, for all broods.
Removal of water sprouts, or '"suckers," on which many first-
brood eggs are concentrated, may reduce the egg infestation by a third.
It is common practice to remove the suckers whenever spring work permits.
The most effective time is a week or 10 days before blossoming, when the
egg deposit is nearly complete but before extensive hatching has caused
crowding of larvae and their migration from the limited sucker foliage.
Shoot thinning of wine and table-grape varieties removes shoots
where the foliage is dense, and consequently a large percentage of the
first-brood larvae are removed at the same time. As a result, second-
brood eggs are concentrated on a reduced number of leaves rolled by the
remaining first brood. Leaf thinning, which is practiced with these va-
rietiones to increase the amount of light reaching the developing fruit, be-
gins when the second brood of adults are active. If the first leaf thinning
is delayed until egg deposition by the second brood is complete, the small
number of egg-infested rolled leaves can be removed with a slight additional
cost for labor, and a reduction of infestation by the second brood can be
acoompliehed. Observations on the effects of thinning of shoots and leaves
have been made by the writer on the Ribier variety only.
Although the larvae feed in protected looatione during most of
theirol development, the protection is interrupted when they leave the webbed-
togethor leaves or old rolls to make new rolls at the end of the group-feed-
ing period# early in the fourth stadium of their growth. Applying inseoti-
oides before rolling occur forces larvae to feed upoh poisoned foliage
within new rolled, Rnd they die before they have eaten more than 16 or 20
percent of the foliage neeeaso ary for their development. If the larvae are
not killed in their firot roll they may be reached by poison later, since
more than one roll iN made during their development, but foliage injury
which might hAve been avoided aocurn in the meoatifme
As a rule there IN little foliage or fruit damage if control ise
applied during the development of the first brood of larvae, Trhen the
control is delayed until the second brood of larvae appear, loea of foliage
will be inoreaed tbut only minor fruit damage will oeoeur, except in very
hoavy 1nfR.t4t1ons The Only A4vnt4ge in delaying iN that, by observing
the first lbrood, it will be eaoiler to etlmito the probable infestation
thAt will occur 14ters Applications of control measures during the third
brood will be of value only feor 2 tea-m4turing grapes, such a@ the Emperor
variety. inpe there hag been no Ptudy of inaoetide-remdue problems
In connoction with control meaure for th@ grape leaf folder, reoommenddAon
owanot be d d'or control of thoe third brood.
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Figure 1.-Average number of grape Loast folder noths taken per
trap per day during 4 years of trapping with malt-eirp bait
UNIVERSITY OF FLORIDA
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