Fifth-instar larvae spin a grayishwhite
silken cocoon in which they
pupate. The pupa is approximately ¼
Ground surveys for immature
insects by vineyard, regulatory, and
UC Cooperative Extension personnel
were more fruitful. Almost 30 individual
properties inNapa County are now
presumed positive for at least one life
stage of L. botrana. By November 2009,
trapping efforts had ended for the season,
concurrent with the lack of a population
in the adult stage.
In the Mediterranean region, L.
botrana typically completes two to three
generations per year. Using 50ºF (lower)
and 86ºF (upper) thresholds, we tentatively
estimate degree-days Fahrenheit
to be 833 for the first generation and 904
for the remaining generations.
First generation flights may begin
near bud break and continue for four
to five weeks; males begin emerging
roughly one week before females.
Adults live one to three weeks, fly at
dusk (above 54ºF), andmate in flight (1
to 6 days after emergence). Females
generally mate once in their lifetime.
Egg-laying begins one to two days
aftermating, with each female laying 80
to 160 eggs. Eggs of the first generation
— laid singly on flat surfaces near or
within the flower cluster—hatch in 7 to
11 days. Larvaeweb together individual
flowers to form “nests” prior to and
during bloom, and feed inside the web.
Under optimal conditions of 80º to
85ºF and 40% to 70% relative humidity,
larval development is completed in 20
to 30 days. Pupae form inside webbed
cocoons in the flower cluster, in a
folded lobe of a leaf blade, under the
bark, or in soil cracks. Adults emerge 6
to 14 days after pupation.
Eggs of second and third generation
females — laid singly on shaded
berries — hatch in 3 to 5 days. A grape
cluster is typically infested with multiple
larvae that feed individually inside
berries. Larvae fed on higher-quality
food (ripe fruit or fruit infested with
cinerea) grow into larger,
longer-lived adults that lay greater
numbers of eggs. Therefore, later-season
generations have the potential to
cause greater crop damage than earlyseason
In autumn, nights longer than 11
hours during egg and/or larval development
initiate diapause (a resting
state). A diapausing pupa withstands
colder temperatures than a non-diapausing
pupa and can tolerate even the coldest
northern European winters. In early
February, during post-diapause development,
prior to adult emergence,
pupae may die at temperatures below
L. botrana larvae feed on all parts of
the flower cluster in early spring, but
more importantly they feed on berries in
midsummer and again in late summer,
continuing through harvest and into
leaf-fall. Feeding triggers infections by
the fungus Botrytis cinerea and other rot
organisms resulting in bunch rots that
are the main cause of fruit loss.
Larvae of the first generation of L.
botrana hatch from eggs laid in flower
clusters and damages portions of the
Second generation larvae hatch
from one egg per berry prior to veraison,
starting about when berries are
pea-size and feed inside webbing.
Damage is caused by direct feeding on
the berries. A dark spot surrounds the
point of larval feeding and several
berries can be damaged.
Third generation larvae can cause
the most damage to clusters, preventing
them from being harvested for
wine grape production. Larvae penetrate
and feed on ripening fruit immediately
Infested clusters contain shriveled
berries, webbing, and excrement.
Feeding holes can be seen in several
berries. Shreds of berry epidermal tissue
loosely attached to pedicels are
present, as are dry, somewhat intact
“skins” of fully excavated berries.
Bunch rot is present, and depending
on climate, the summer bunch rot complex
will develop which includes secondary
Monitoring methods for L. botrana
in California vineyards may not be
identical to strategies used in Europe
or other regionswhere this pest is common;
however the objective is the same
— to decrease yield losses caused by
the feeding damage of this insect.
Strategically timed insecticide applications
are required to control this pest
and, depending on the generation targeted
and the material applied, it is
essential to identify either the beginning
of egg laying or egg hatch.
Monitoringmale flights with a commercially
available L. botrana pheromone
lure over the entire 2010 grape
growing season is advised at this time.
Red delta sticky traps, identical to
those used for monitoring vine mealybugs,
are ideal for this purpose, and
should be attached to the trellis immediately
above the canopy. Place one
trap per 30 vineyard acres, or at least
one per ranch in small vineyards.
The lure should be replaced according
tomanufacturer’s instructions, and
insects removed from the trap bottom
after counting. Replace soiled traps as
needed to maintain a sticky bottom.
Trapping for L. botrana males should
begin at bud break and trap-catch
numbers should be recorded weekly.
Trapping is used to determine when
the adults are active, which helps predict
egg-laying activity. There is no
close correlation between the number
of trapped males and actual population
densities. If very few or no males
are caught, little to no damage would
be predicted; however, if any males are
trapped, it increases the likelihood that
webbing found in clusters is caused by
First generation — Once peak trap
catch has likely been reached, begin to
observe 100 flower clusters per block
(1 cluster per vine) and look for eggs of
the first generation, which are commonly
laid on the peduncle (cluster
stem). Eggs are lentil-shaped, but
slightly smaller. Take note of the egg
color and the time it takes to change
fromwhite (freshly laid), to yellow, followed
by black immediately prior to
hatching. A hatched egg can be recognized
by the outer shell that remains. If