STORED-PRODUCT AND QUARANTINE ENTOMOLOGY Selection of Cold Injury Treatments to Facilitate Release of the Parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae) Reared on the Rice Weevil (Coleoptera: Curculionidae)

The use of cold treatments to kill the rice weevil, Sitophilus oryzae (L.), before eclosionbut allow theparasitoidAnisopteromalus calandrae (Howard) tocompletedevelopment and eclosion was examined. Cold tolerance, crystallization temperature, and developmental stage of rice weevilswere examined at 2-d intervals between 18 and 30d after riceweevil oviposition. Themedian crystallization temperaturedropped from 216 to2248Cover this time, andcold tolerancewas lowest between day 20 and 24. Based on these data, rice weevil immatures were exposed on days 18, 19, 21, 22, 23, and 24 after oviposition for 2 h to various subzero temperatures. Hosts were exposed to parasitoids for oviposition on day 20. Before parasitization, rice weevils were either frozen internally by exposure to 2258C, or were subjected to nonfreezing chilling injury by exposure to 2128C. Rice weevils exposed to cold after parasitization were subjected to chilling injury by exposure to either 212 or 2108C. Freezing rice weevil larvae before parasitization resulted in poor production of parasitoids and a sex ratio favoring males. Exposure to 2128C for 2 h, 2 or 3 d after parasitization resulted in production of parasitoids similar to unchilled controls, and a slightly higher female-tomale ratio than the controls. The production of A. calandrae was better after exposure to 2108C, but at this temperature some rice weevils eclosed. The treatment of 2 h at 2128C, 3 d after parasitization gave the best parasitoid survival and ensured rice weevil mortality.