Overwintering survival of bagworms, Thyridopteryx ephemeraeformis (Lepidoptera: Psychidae): Influence of temperature and egg cluster weight

The present study relates the survival rate of bagworm eggs to extreme winter temperature and weight of egg clutches. The eggs were collected in the spring of 2009 at 104 locations in the mid-western United States of America across a latitudinal range from 36.5-41.5 °N. Egg survival after a 1-week incubation period was overdispersed, suggesting that survival of individual eggs within a clutch is highly correlated. Logistic regression analysis revealed that the survival of eggs, assessed after 1 or 12 weeks of incubation, significantly increases with the weight of egg clutches and increasing minimum winter temperature (expressed as the maximum temperature during the coldest day of winter). Lethal temperature for 50% of egg clusters was -14 °C for clusters weighing 0.1 g and -18.1 °C for 0.4 g clusters. The regression model developed here provides a tool to forecast the persistence of bagworm populations in recently colonised locations in Michigan, United States of America and southern Ontario, Canada.