Desiccation resistance in pre-diapause, diapause and post-diapause larvae of Choristoneura fumiferana (Lepidoptera : Tortricidae)

Desiccation resistance was examined in pre-diapause, diapause and postdiapa use larvae of the spruce budworm, Choristoneura fumiferana (Clemens), in te rms of passive water evaporation under three desiccation conditions: freeze -drying, desiccant-drying at 2 degreesC and desiccant-drying at 18 degreesC . Diapausing second instar larvae and post-diapause non-feeding second inst ar larvae showed strongest desiccation resistance: a significant amount of water was retained after repeated drying under desiccating conditions, whil e pre-diapause first instar larvae and post-diapause feeding second instar larvae lost almost all their water content after one or two drying cycles. A hibernaculum covering had no effect on water evaporation. While dead larv ae tended to lose significantly more water than their living counterparts, particularly among first instar larvae, such an impact was much weaker amon g diapausing second instar larvae. Desiccation resistance was lost when pos t-diapause second instar larvae were allowed access to water while the leve l of desiccation resistance was maintained or enhanced when the larvae did not have access to water. These results are discussed in the context of ove rwintering ecology of the species and possible mechanisms for the desiccati on resistance are also discussed.