A and B, Courtesy Conn. Agric. Exp. Stn.; 
C, F-506692 
Figure 82.—Forest tent caterpillar, Malacosoma disstria: 
A, adults; B, full-grown caterpillar, showing keyhole 
spots along the dorsum; C, caterpillars at rest on trunk 
and branches of an aspen. 
during the 1960’s, mostly defoliating water tupelo on a gross area of 17,000 
hectares (2/3, 1/47). Damaging populations arose again in 1981, including Loui- 
siana, North Carolina, Kentucky, and Alabama (58/). In general, tree mortality has 
not been severe, but losses in reduced growth following defoliation have been great. 
Studies in Minnesota indicate that there 1s about a 70 percent reduction in basal area 
growth of aspen during the first year of heavy defoliation. About 90 percent 
reduction also occurs during the second year of heavy defoliation, plus about 15 
percent reduction during the year of recovery. Total reduction for the 3-year period 
averages about 58 percent (349). Heavy defoliation of bottom-land gums in the 
South results in substantial mortality and dieback, as well as severe reduction in 
annual growth. In the Northeast, heavy defoliation in sugar maple orchards not only 
causes serious injury to the trees, but also a reduction in the quantity and quality of 
the sap. Outbreaks in recreational areas adversely affect business because of the 
nuisance created by migrating caterpillars and the midwinter appearance of defoli- 
ated trees during the tourist season. Discussions of the effects of defoliation on 
quaking aspen in Canada are published (570, /035). Outbreaks have been associ- 
ated in eastern and central Canada with a cool winter and warm spring 2 to 4 years 
earlier (628). 
Outbreaks usually subside after 3 or 4 consecutive years of defoliation. Several 
adverse environmental factors are responsible for population declines. Mortality of 
pharate larvae, possibly caused by low winter or spring temperatures, may be quite 
high (1/279, 1346, 1347). Harsh weather conditions may cause death of large 
numbers of the early instars. Excessively high temperatures later in the spring may 
kill large numbers of adults and seriously reduce the viability of newly laid eggs. 
Mortality of the late instars may be severe or complete as a result of starvation in 
heavily or completely defoliated stands. A polyhedrosis virus disease sometimes 
kills enormous numbers of larvae in the late stages of outbreaks (//45). The 
sarcophagid parasite, Sarcophaga aldrichi Parker, often becomes extremely abun- 
dant during the late stages of outbreaks in the Lake States and greatly aids in 
termination of outbreaks (576). Other natural enemies include many species of 
insect parasites (1/345). Bacillus thuringiensis and various chemical insecticides 
may be used to control larvae (527). 
205 
