Integrated Pest Management for Christmas Tree Production: A ...

Figure 1. Gypsy moth egg mass.
Courtesy of Pennsylvania DCNR
Forestry Archive, Bugwood.org
(#5020037)
Figure 2. Larvae “ballooning,”
or dropping down onto new
hosts via silken thread.
Courtesy of Brian Schildt, PDA
Figure 3. Gypsy moth larvae
and silk covering Douglas-fi r
buds. Courtesy of Brian Schildt,
PDA
Figure 4. Maturing caterpillar
with red and blue spots and
yellowish lines running the
length of the body. Courtesy of
Brian Schildt, PDA
Biology and Life Cycle
Eggs overwinter in the egg masses protected
somewhat by the hairs from the female’s
abdomen (Figs. 1 and 6). The masses may
contain up to 600 eggs, which are rounded
and tan. Egg masses darken with age, and
hatching occurs between late April and
mid-May when oak leaves are expanding.
Newly hatched larvae (caterpillars) remain
on the egg mass for a few days before moving
to the newly developing leaves. If the
population is high or the host is not suitable
for development, larvae will “balloon” to
new hosts by dropping down from a silken
thread (Figs. 2 and 3). Spring winds can
carry the young caterpillars up to a mile.
During this phase, gypsy moth larvae are
frequently seen on clothing when working
outdoors. The irritating hairs of the fi rst
instar caterpillars may cause contact
dermatitis for some people.
Larvae feed for 6–7 weeks, gradually
increasing in size and appetite. Young larvae
remain in the tree’s foliage day and night,
but their feeding pattern changes when they
are half grown (Fig. 4). The more mature
larvae move down the tree to take refuge in
a cool, shady place during the day and feed
in the canopy at night.
By late June to early July, the larvae fi nd
a sheltered place to pupate (Fig. 5). About
2 weeks are required before the adults begin
to emerge, with the male moths appearing
several days before the females. When
the female moths emerge, they may crawl
a short distance to an elevated spot or stay
near the pupal case to emit a pheromone
to attract the male moths. After mating occurs,
females deposit one to two egg masses
before dying (Fig. 6). Neither male nor
female moths feed during their short lives.
Egg masses overwinter until the following
spring. One generation is produced per year
in Pennsylvania.
Figure 5. Gypsy moth pupae suspended from
tree limbs. Courtesy of PDA
Monitoring and Management
Strategies
Plantation Establishment
• Plant the crop away from hardwood stands
such as aspen or oak or other preferred
hosts of the gypsy moth.
Preseason
• Scout year-round for gypsy moth egg
masses both in the plantation and in
surrounding woodlots.
• Monitor egg masses for fi rst signs of
hatching.
• Contact a regulatory agency or county
extension offi ce to obtain information
about specifi c management options in the
area and about shipping Christmas trees.
Growing Season
• Growing degree days: 90–448 GDDs is
the treatment window for the larvae.
• When larvae are small, consider
spraying with a microbial or other type
of insecticide.
• To help monitor populations, use a
synthesized female pheromone trap to
look for male moth emergence.
• At the end of the season, evaluate results
and update records.
Figure 6. Female
gypsy moth over
egg mass. Courtesy
of Hannes Lemme,
Bugwood.org
(#1260007)
NEEDLE DISCOLORATION AND INJURY ................................................................................................................................................................................................................................................ 46