Tufted Apple Budmoth (Lepidoptera: Tortricidae): Effects of Constant Daylengths and Temperatures on Larval Diapause Development 1

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Abstract
Diapausing larvae of a laboratory strain of tufted apple budmoth, Platynota idaeusalis (Walker), were reared individually to larval-pupal ecdysis under different constant photoperiods and temperatures. Duration of larval instars 1 to 3 was not increased in diapausing insects (reared under short daylength) relative to nondiapausing larvae (reared under a long daylength), but there was a significant increase in duration of instars 4 and 5. Most of the increase in the number of days to larval-pupal ecdysis in diapausing insects occurred during additional larval instars of extended duration. Insects that diapaused under a 14-h daylength had significantly shorter times to larval-pupal ecdysis than those insects that diapaused under 10-, 11-, or 12-h daylength. At 10-h daylength, diapause duration and number of larval instars decreased with increasing temperature. Diapausing, field-collected larvae were reared to larval-pupal ecdysis under different photoperiods at 21°C. Diapause termination was spontaneous under both long and short days, and did not require chilling. Diapause duration was much shorter under long daylengths, and decreased under both long and short daylengths with later collection dates from autumn throught winter. Sensitivity to daylength was maintained through the end of winter; long day lengths apparently terminate diapause in the spring in field populations.