The influence of summer and fall photoperiod on larval development time and pupal weight in Phyllonorycter mespilella (Hübner) was measured in the laboratory. The offspring of mothers originating from either summer or fall photoperiod were split between summer and fall photoperiod environments to complete their development to the pupal stage. The durations of the sap-feeding and tissue-feeding larval stages and pupal weight were measured for larvae from these 4 treatment combinations of maternal and larval photoperiod. Sapfeeding duration and tissue-feeding duration were longer and pupal weight was higher at fall larval photoperiod than at summer larval photoperiod. Individuals reared at summer larval photoperiod emerged as adults, and those reared at fall larval photoperiod entered diapause dormancy as pupae. The sap-feeding duration of diapausing larvae was higher for individuals from fall maternal photoperiod than for those from summer maternal photoperiod. Maternal photoperiod had no effect on tissue-feeding duration or pupal weight. A small proportion of larvae reared at summer larval photoperiod had extremely long sap-feeding durations and entered diapause dormancy. Photoperiod-induced changes in larval development may explain the prolonged, late-summer development times that have been frequently observed in Phyllonorycter species.
