EFFECT OF PARASITISM BY ANAPHES SP (HYMENOPTERA, MYMARIDAE) ON THE COLD-HARDINESS OF LISTRONOTUS-OREGONENSIS (COLEOPTERA, CURCULIONIDAE) EGGS

The cold hardiness of egg parasitoids is critical to their survival in winter because these organisms have little control in the choice of their overwintering site. The supercooling points of Listronotus oregonensis eggs increased from -24.9 to - 22.1-degrees-C as eggs matured. When these eggs were parasitized by Anaphes sp., their supercooling point remained stable at -22.9-degrees-C throughout the development of the parasitoid. Anaphes sp. maintained its cold hardiness by increasing its levels of glycerol and fructose. When the parental generation was exposed to a combination of low temperature and short photo-period, the supercooling point of the daughter generation (F1) was significantly decreased. A further decrease in the supercooling point was observed when F1 individuals were stored at 3-degrees-C for 14 or 20 days. These data show that local extinction of populations overwintering in nonsheltered habitats is probably common in southwestern Quebec.