1961] 
Insect Control Programs 
77 
area from France in 1869 by a misguided naturalist who believed 
that he could cross it with silkworms. Moths escaped from his breed- 
ing colony, but it was not until 1889 that the first severe outbreak 
defoliated fruit and shade trees in many towns of eastern Massachu- 
setts. Control work was started by the state and apparently was 
successful, for populations were so low by 1899 that control operations 
were ended. The moth soon again built up extensive populations, 
and control work was resumed in 1905, but it had spread by this 
time to western Massachusetts and parts of Maine, New Hampshire 
and Rhode Island. In 1906, Congress voted aid to the infested states 
to help prevent the spread of the moth, but despite all efforts it con- 
tinued to expand its range. 
Biology and Nature of the Damage 
The gypsy moth has a single generation per year. The winter is 
passed in the egg stage, and in New England the larvae hatch in mid- 
spring and feed through May and June, entering the quiescent pupal 
stage in early July. The larvae feed on a wide variety of broad-leaved 
trees and shrubs, especially oak, willow, poplar, birch, fruit trees and, 
in heavy infestations, even hemlock and pine. Dense populations may 
completely defoliate large jireas of forest, weakening many trees and 
killing others outright. 
The heavy-bodied female does not fly, but puts out a powerful scent 
to which the strorTg-flying male responds, even to extremely minute 
amounts carried on the air great distances, by flying upwind until 
contacting the source individuals and copulating with them. 18 The 
female deposits her eggs on tree trunks, fences, rocks and other solid 
objects. The young larvae spin silken threads on which they are 
easily spread by the wind before they start to feed. 
According to Campbell 4 the strong fluctuations in abundance of 
the moth are density-reactive, a most critical factor in this reactivity 
being the larval behavior. At low densities, the caterpillars tend to 
descend to the leaf litter to rest during the daytime, and feed mainly 
at night out on the foliage. When density is intermediate, the larvae 
rest during the day under loose bark on the tree trunks, a habit that 
has been used to advantage in control work (bands of burlap placed 
around trunks of infested trees are removed daily and the caterpillars 
found beneath them are destroyed). At high densities, the larvae 
remain on the foliage day and night, and are subject to heavy losses 
due to disease, desiccation and attack by ichneumon-wasp parasites. 
Population “crashes” are correlated with previous high densities of 
larvae. 
