SPRING EMERGENCE BY LARVAE OF THE EASTERN TENT CATERPILLAR (LEPIDOPTERA, LASIOCAMPIDAE) - A HEDGE AGAINST HIGH-RISK CONDITIONS

Temperature-dependent thermal responses of postdiapause eggs of the ea stern tent caterpillar, Malacosoma americanum (F.), one of the earlies t spring emergent caterpillars in eastern North America, were describe d from a laboratory study of the effects of constant temperature on la rval emergence from egg masses collected weekly and a field study of e mergence of the 1st larva per egg mass (H-0) and subsequent daily emer gence of larvae from egg masses on host trees in Maryland. Cumulative weekly increases in thermal units decreased the time of H-0 of field-c ollected eggs incubated at controlled temperatures but had no effect o n the lower larval development threshold (T-b). The number of larvae e merging daily from egg masses held at controlled temperatures was temp erature-dependent, asynchronous, and indicated that diapause of the ph arate larva was terminated before 31 January. For 3 consecutive years, the H-0 among annually deposited egg masses on the same tree was asyn chronous, several days lapsing between the 1st and last H-0. The daily rate of emergence among individual egg masses on the same tree also w as asynchronous. The number of days to estimated median larval emergen ce (E-50) was variable, and the length of larval emergence averaged 12 +/- 1.2 d. Daily emergence appears to be relatively independent of te mperature. Thus, reducing the risk of mortality of early instars from late winter storms by asynchronous emergence in early spring is a beha vior that is apparently random and appears to be under genetic control .