EFFECTS OF EARLY TEMPERATURE EXPOSURE ON DIAPAUSE DEVELOPMENT OF SPRUCE BUDWORM (LEPIDOPTERA, TORTRICIDAE)

Diapausing larvae of spruce budworm, Choristoneura fumiferana (Clemens ), were exposed in their early stage of development to different tempe ratures for various durations with or without subsequent cold storage periods at 2 degrees C. The results suggest there exists an early deve lopmental window or a phase, during which a diapausing larvae requires moderate temperature to fulfill its development. Both degree and dura tion of temperature exposures during the early diapause stage had sign ificant effects on diapause intensity and proportion of larvae capable of accomplishing diapause development under certain conditions. In ge neral, longer duration of exposure to higher temperatures increases di apause intensity and reduces larval survival. Subsequent temperature t reatment with the cold storage makes this phenomenon more obvious. Var iation in emergence time was reduced substantially by a prolonged cold storage period. The implication of the results for the overwintering process of the species was discussed.