It's tough being a bug in winter, yet some creatures, like goldenrod gall fly larvae, miraculously manage to survive icy winters and emerge unscathed in spring. But surviving frosty conditions is only part of the problem; since water is locked up in ice, bugs are also in danger of drying out. So how do the larvae manage to overwinter? Jason Williams and colleagues at Miami University wondered whether the larvae gradually develop both cold tolerance and resistance to water loss as temperatures plummet between autumn and winter(p. 4407).
Williams explains that in early autumn, few larvae can survive subzero temperatures. However, by winter the bugs develop freeze-tolerance, churning out sugar-like substances called cryoprotectants that act as anti-freeze, so that the youngsters can endure a frosty –20°C. Even more impressive,goldenrod gall fly larvae become desiccation resistant and can compete with desert beetles when it comes to cutting their water losses. But are these two remarkable abilities linked? From early autumn to mid-winter, the team measured larval survival rates after freezing, as well as the bugs'cryoprotectant levels and resistance to water loss. They found that a seasonal decline in water loss rates was directly linked to boosted cryoprotectant levels in the insects' circulatory systems. Williams concludes that the gall flies' anti-freeze doesn't just stop the insect from turning into an icicle;it may also conveniently protect larvae from the perils of dehydration.