EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON DIAPAUSE OF 2 APHELINUS SPP (HYMENOPTERA, APHELINIDAE) PARASITIZING THE RUSSIAN WHEAT APHID

The effects of photoperiod and temperature on the diapause of Aphelinus varipes (Foerster) from Kazakhstan and Aphelinus near varipes from Alberta, which both attack Russian wheat aphid, were studied in the laboratory. At 20-degrees-C, 50% of A. varipes entered diapause when the photoperiod was between 12.5L:11.5D and 13L:11D whereas 50% of A. nr. varipes entered diapause when the photoperiod was around 14L:10D. Diapause induction was close to 100% at 11.5L:12.5D for both species. Maximum sensitivity to photoperiod occurred 2 days after parasitization for A. varipes and 3 days after parasitization for A. nr. varipes. At 30-degrees-C, the proportion of wasps entering diapause was reduced to 40 and 72% for A. varipes and A. nr. varipes, respectively. Exposing diapausing mummies to temperatures from 10 to - 10-degrees-C for 4-20 weeks shortened the postdiapause developmental time. Survival was lowered by exposing mummies to - 10-degrees-C for over 8 weeks. Postdiapause developmental rate was directly temperature dependent. The lower threshold and thermal constant for postdiapause development were estimated to be 10.3-degrees-C and 189 degree-days (DD) for A. varipes and 7.41-degrees-C and 204 DD for A. nr. varipes.