Links Between Desiccation Resistance and Cold-Tolerance in an Overwintering Insect: Seasonal and Geographic Trends
In this dissertation, I have examined possible links between physiological parameters associated with survival at low temperature and water balance of an overwintering insect. The first study provided a seasonal characterization of cold-tolerance and desiccation resistance in overwintering larvae of the goldenrod gall fly, Eurosta solidaginis. From September 20 to October 30 larvae exhibited a gradual increase in cold-tolerance that was associated with increases in cryoprotectants. In contrast, larvae exhibited a two-phase increase in desiccation resistance. The first was a dramatic six-fold reduction in rate of water loss that occurred between October 3 and October 16 as the gall tissue senesced. The second, more subtle reduction occurred between October 16 and December 11 and was associated with cryoprotectant production. The second study examined cues for the rapid, seasonal increase in desiccation resistance of E. solidaginis larvae associated with senescing of the gall tissue. Desiccation resistance increased dramatically within three days of removal from the gall, and was primarily due to reductions in respiratory water loss as larvae entered dormancy. This study illustrated that dormancy in overwintering insects that was primarily thought to be an adaptation to conserve metabolic fuels, also may be essential for water conservation. I also examined cold-tolerance and desiccation resistance in three widely separated populations of overwintering E. solidaginis larvae from Michigan, Ohio and Alabama. Larvae from the most northern population had higher concentrations of the cryoprotectant glycerol, were more cold-tolerant, and had lower rates of overall water loss after acclimation to 5 °C. In contrast, southern larvae had lower rates of metabolism and transpiratory rates of water loss after acclimation to 20 °C. Lastly, I examined possible links between extracellular solute regulation and cell volume maintenance in larvae subjected to dehydration and freezing. After dehydration, low temperature, and freezing exposures, larvae had lower relative hemolymph volumes and lower than expected hemolymph osmolalities compared to controls, suggesting that hemolymph solutes are regulated and extracellular water was removed during the treatments. There was no substantial movement of ions between fluid compartments in dehydrated or frozen larvae, but cryoprotectants may have accumulated in intracellular fluids during these stresses.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:cold tolerance desiccation resistance freeze cryoprotectants sorbitol glycerol
Date of Publication:01/01/2005