ACTIVITY RHYTHMS OF LEPIDOPTEROUS DEFOLIATORS: III. THE DOUGLAS-FIR TUSSOCK MOTH, ORGYIA PSEUDOTSUGATA (McDUNNOUGH) (LIPARIDAE)

Abstract

Techniques previously described were used to record larval activity on foliage and adult emergence and flight times of Orgyia pseudotsugata (McDunnough) in both constant and naturally varying temperatures. Most larvae hatched in the morning after sunrise; hatching decreased during the day and was minimal at night. Early-instar larvae were active during the day in all temperature regimes studied, and nocturnal activity occurred only when the temperature was at least 20 °C. Young larvae tended to drop from foliage on silken threads with dropping peaks in the morning and afternoon. Late-instar larvae were mainly nocturnal in the constant and varying temperatures. Adult emergence, and flight of males, occurred mainly in late afternoon prior to sunset, and evidence of heightened activity at this same time in the diel was discernible as early as the first and second instars. The possible adaptive value of these rhythms in the insects in nature is discussed.