Relationship Between Supercooling Point and Mortality at Low Temperatures in Indianmeal Moth (Lepidoptera: Pyralidae)

Indianmeal moth, Plodia interpunctella (Hübner), is classiÞed as a freeze-intolerant organism and one of the most cold-tolerant stored-product pests. The objective of this study was to determine the relationship between mortality at low temperatures after minimum exposure and the supercooling point (SCP) for laboratory-reared P. interpunctella at different stages of development. This relationship also was analyzed for Þeld-collected, cold-acclimated Þfth instars. Mean SCP of laboratory-reared larvae (i.e., feeding stage) was consistently above 16 C. Mean SCP of laboratoryreared pupae and adults (i.e., nonfeeding stages) and Þeld-collected, cold-acclimated Þfth instars was consistently below 21 C. The SCP seemed to be the boundary between survival and death for larvae. However, it seemed that a 1-min exposure was not sufÞcient to cause larval mortality at the SCP. Alternatively, for both pupae and adults, the SCP seemed not to play an important role in their survival at low temperatures, with signiÞcant mortality observed at temperatures higher than the mean SCP. Adults were the most susceptible to low temperatures with no survival occurring at 20 C, 3 C above its mean SCP. Results of this investigation demonstrate that P. interpunctella has a different response to low temperatures depending on stage of development and cold acclimation. Classifying P. interpunctella only as a freeze-intolerant organism disregards the occurrence of prefreeze mortality in this species. Therefore, a reclassiÞcation of this species (e.g., chill tolerant or chill susceptible) based on the extent of prefreeze mortality and the temperature and time of exposure at which it occurs is suggested.