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 20, 15, 10, 5, and 0 °C for one week. In contrast, other colonies were acclimated to measure heat tolerance at 20, 25, and 30 °C for one week and 35 °C for two days. Then, the lowest temperature resulting in 50% mortality (LLT50) and the highest temperature resulting in 50% mortality (ULT50) of tested populations were defined. Moreover, changes of sugars and polyols were studied at the end of each thermal regime. The lowest LLT50 was -13.2 °C at 0 °C and the highest ULT50 was 40.1 °C at 35 °C. In the cold acclimation condition, glucose was the highest at 0 °C and reached to 80.9 μmol/g f.w. However, in the heat acclimation condition, the mannitol was the highest at 35 °C and reached to 43.7 μmol/g f.w. Findings indicate that high temperatures due to climate change could be a threat to aphid population size and distribution.