Many overwintering insects in temperate and polar regions

must endure cold and severely desiccating conditions, but most studies of adaptations for winter survival have focused primarily on survival at low temperature, with little consideration of water conservation. However, several authors have emphasized that certain adaptations affect not only coldhardiness but also resistance to water loss (Ring and Danks, 1994; Block, 1996; Danks, 2000), suggesting that both behavioral and physiological adaptations for survival at low temperatures also promote water conservation. Many insects avoid variable and extremely harsh conditions by overwintering beneath leaf litter or snow, where conditions are relatively mild and stable, near 0 °C and 100 % relative humidity (RH) (Marchand, 1996); however, others are exposed to the coldest of ambient winter temperatures and must also resist drying conditions (Danks, 1991). Most insects cannot survive internal ice formation and are termed freeze-intolerant. The seasonal accumulation of glycerol and other low-molecular-mass polyols and sugars, termed cryoprotectants, promotes increased cold-hardiness and resistance to water loss (Lee, 1991). These substances colligatively increase the insect’s hemolymph osmolality, which enhances the ability of its body fluids to supercool (i.e. to remain in the liquid state below the melting point). These substances also act in a similar colligative manner to reduce the vapor pressure deficit between the insect’s hemolymph and the environment and, thus, decrease its rate of water loss. Other insects achieve the same result by decreasing their body water content, which concentrates their hemolymph (Ring, 1981; Rickards et al., 1987). Insects used in studies of adaptation to cold have been collected in a variety of habitats and associated environmental conditions such as in plant stems, under bark and rocks, in soil and within plant galls (Leather et al., 1995). Several species of gall-inducing insect, including the tephritid Eurosta solidaginis (Fitch) (Lee et al., 1995), the olethreutid moth Epiblema scudderiana (Clemens) (Rickards et al., 1987) and cynipids of the genus Diplolepis (Rickards and Shorthouse, 1989; Shorthouse et al., 1980; Sømme, 1964), have been used in cold-hardiness studies, partly because it is easy to collect large numbers in mid-winter. Wasps of the genus Diplolepis, all of which induce galls on wild roses (Shorthouse, 1993), are particularly useful for comparative studies of cold-hardiness because some species 2115 The Journal of Experimental Biology 205, 2115–2124 (2002) Printed in Great Britain © The Company of Biologists Limited 2002 JEB4053