Effects of photoperiod and temperature on preimaginal development and summer diapause of Chrysocharis pubicornis (Zetterstedt) (Hymenoptera: Eulophidae), a pupal parasitoid of leafminers (Diptera: Agromyzidae)

Abstract

The preimaginal development of Chrysocharis pubicornis was studied at different temperatures and 14L:10D photoperiod. The lower developmental threshold was 7.4 and 7.2°C, and the thermal constant was 297.4 and 307.5 degree-days for males and females, respectively. The effects of combinations of different temperatures and photoperiods on larval diapause induction and termination were also examined. Larval development showed a short-day type response affected by temperature. The percentage of individuals entering diapause increased with the temperature and photoperiod. The critical photoperiod for diapause induction was between 12 and 14 h at 25°C, whereas at 15 h and 20°C the diapause rate did not reach 50% within the photoperiod range tested. Regardless of the photoperiod, diapause terminated at 15°C but was maintained at 25°C. At 20°C, 90% of individuals terminated diapause at 12 h photoperiod but only 16% at 16 h photoperiod. A significant effect of the photoperiod on the post-diapause emergence pattern of wasps was observed at 15°C. From these results, it is considered that summer diapause enables C. pubicornis to synchronize its occurrence with that of the garden pea leafminer, Chromatomyia horticola.