The bagworm Thyridopteryx ephemeraeformis (Haworth) is univoltine and overwinters as diapausing eggs within the silken bag from the female moth. We have sought to determine whether selection of this overwintering site protects eggs against desiccation and low temperature injury. Bag-enclosed eggs retained water nearly three times more effectively (net water loss rates were lower) than naked eggs. A similar trend was noted in the ability of eggs to withstand prolonged exposure to subzero temperatures: naked eggs were four times more susceptible to chilling injury compared with those tucked inside a bag. Plastic or tissue paper artificial bags did not mimic the protection against cold. The eggs contained low levels of glycerol and sorbitol, suggesting no major role for these cryoprotectants. Bagworm eggs are not freeze tolerant, and their high water content implies that they have neither been enhanced for water conservation nor cold hardiness. These observations indicate that use of the female bag as the overwintering site is crucial to high winter survival by T. ephemeraeformis.
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Vol. 95 • No. 4