Thermal tolerance of adult greenbug, Schizaphis graminum: Different role of sugars and polyols

The Greenbug Schizaphis graminum (Rondani), one of the major pests of cereals, overwinter as adults and nymphs in temperate regions. The aphid population increases in early spring as the weather conditions become favorable, but it gradually decreases in mid-June as air temperature rises. Adult aphid colonies were acclimated to measure cold tolerance at ۲۰, ۱۵, ۱۰, ۵, and ۰ °C for one week. In contrast, other colonies were acclimated to measure heat tolerance at ۲۰, ۲۵, and ۳۰ °C for one week and ۳۵ °C for two days. Then, the lowest temperature resulting in ۵۰% mortality (LLT۵۰) and the highest temperature resulting in ۵۰% mortality (ULT۵۰) of tested populations were defined. Moreover, changes of sugars and polyols were studied at the end of each thermal regime. The lowest LLT۵۰ was -۱۳.۲ °C at ۰ °C and the highest ULT۵۰ was ۴۰.۱ °C at ۳۵ °C. In the cold acclimation condition, glucose was the highest at ۰ °C and reached to ۸۰.۹ µmol/g f.w. However, in the heat acclimation condition, the mannitol was the highest at ۳۵ °C and reached to ۴۳.۷ µmol/g f.w. Findings indicate that high temperatures due to climate change could be a threat to aphid population size and distribution.