Canadian Forest Service Publications

Overwintering survival of bagworms (Lepidoptera: Psychidae): influence of temperature and egg cluster weight. 2013. Rhainds, M.; Régnière, J.; Lynch, H.J.; Fagan, W.F. The Canadian Entomologist 145: 77–81.

Year: 2013

Issued by: Atlantic Forestry Centre

Catalog ID: 34606

Language: English

Availability: PDF (request by e-mail)

Mark record


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.

Plain Language Summary

The bagworm, Thyridopteryx ephemeraeformis, is a major pest of juniper, arborvitae, and many other ornamental urban trees. The historical records from the last 150 years indicate that the distribution of bagworms in the United States does not extend north of Indiana. Over the last 5 years or so, bagworms have become established in the Windsor area. We evaluated potential survival of overwintering eggs using broad-scale field data and demonstrated a low rate of egg survivorship for a maximum daily temperature of -17°C, a threshold that is rarely reached in the Windsor area; thus, bagworm eggs are expected to survive most winters in Windsor. Because of heavy motor-vehicle traffic in the area and the risk of human-assisted movement of ballooning larvae, the situation with bagworms in the Detroit–Windsor corridor is of concern. In biological terms, it is similar to the geographic expansion of gypsy moth following its introduction to North America.