Oxidative stress and antioxidants in overwintering larvae of cold-hardy goldenrod gall insects

Antioxidant and pro-oxidant systems were studied in overwintering larvae of two cold-hardy gall insect species, the freeze-tolerant fly Eurosta solidaginis and the freeze-avoiding moth Epiblema scudderiana. An increase in the levels of the oxidized form of glutathione suggested slight oxidative stress in both species during the winter. Freeze-tolerant Eurosta solidaginis larvae generally had decreased activities of antioxidant enzymes in the winter, indicating that these larvae do not face increased challenge from oxidative stress during the numerous freeze-thaw events they experience. Instead, existing defences must be sufficient to prevent any damage. By contrast, increased winter activities of antioxidant enzymes in freeze-avoiding Epiblema scudderiana suggest that these larvae must defend against the formation of reactive oxygen species. This may result from the oxidative nature of winter metabolism in these larvae, as well as a dependence on lipid oxidation as their fuel over this season. Xanthine dehydrogenase activity decreased dramatically in both species during the autumn, reducing the potential for the formation of the pro-oxidant xanthine oxidase. Indeed, xanthine oxidase activity fell to undetectable levels by winter in Epiblema scudderiana and was not detectable at any time in Eurosta solidaginis.