COLD TOLERANCE OF PSEUDALETIA UNIPUNCTA AND PERIDROMA SAUCIA (LEPIDOPTERA: NOCTUIDAE)

Pupae and 3rd-instar larvae of Pseudaletia unipuncta (Haw.) survived longer at 0 and −2°C than other immature stages, and insects reared at 15°C were more cold tolerant than those reared at 20°C. Egg survival at 0°C varied greatly among replicates suggesting genetic differences among females. No adults survived 2 weeks at 0°C. Peridroma saucia (Hub.) would not rear satisfactorily at 15°C and, other than eggs, all stages tested were from rearings at 20°C. Eggs from adults at 15°C were more cold tolerant than those from adults at 20°C. There were no differences in survival among any of the larval stages or pupae. Some adults survived 6 weeks at 0°C. No stage of either species survived over 8 weeks at 0°C nor 4 weeks at −2°C indicating that overwintering on the Canadian prairies is unlikely.