Supercooling point variability in the Indian meal moth, Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

Factors affecting the supercooling point (SCP) of the Indian meal moth, Plodia interpunctella (Hübner), were investigated under various conditions. The effects of geographic origin, time under laboratory conditions, laboratory diet, stage of development, age within stage, and season on P. interpunctella SCP were examined. Overall, SCPs ranged from ?28.6 to ?2.4 °C. At the times of collection, differences in SCP between field-collected individuals and individuals from laboratory sources were negligible. The minimum observed SCP for most of the cultures tested soon after collection was below ?20 °C. After 7 months under laboratory conditions, the mean SCP of field-collected and laboratory-reared cultures remained unchanged. No particular trend in SCP was observed when comparing cultures from northern and southern regions. Differences in laboratory diets did not affect mean SCP. Mean SCP for 1- and 4-d-old eggs was similar. Eggs (?24.4 °C), first instars (?23.5 °C), pupae (?22.2 °C), and adults (?22.4 °C) had lower mean SCPs than later instar larvae (?14.4 to ?11.6 °C). When confined in the laboratory for 8 months under conditions which were not controlled, monthly mean SCP for the same culture varied by as much as 5.7 °C. Plodia interpunctella appeared to regulate its SCP as the season changed, with a relatively high mean SCP during summer and a marked decline of more than 10 °C in fall. The SCPs obtained in this study suggest that very low temperatures may be needed for disinfestation of P. interpunctella at all stages of development.