Effects of extreme, fluctuating temperature events on life history traits of the grain aphid, Sitobion avenae

Altered temperatures affect insects' life history traits, such as development period and fecundity, which ultimately determine population growth rates. Understanding insects' thermal biology is therefore integral to population forecasting and pest management decision-making such as when to utilise crop spraying or biological control. Aphids are important crop pests in temperate regions, causing considerable yield losses. The aphid thermal-biology literature is, however, heavily biased towards the effects of rising mean temperatures, whereas the effects of fluctuating, extreme climatic events (e.g., heat waves and sub-zero cold periods) are largely overlooked. This study assessed the effects of laboratory-simulated heat waves and sub-zero cold periods on the survival, development period, and fecundity of the grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae: Microsiphini), in addition to assessing maternal effects on the birth weight and development period of the offspring of exposed individuals. Exposure to heat stress periods (total of 16h at 30 degrees C) significantly reduced aphid fecundity and increased physiological development period (in day-degrees) resulting in a reduced population growth rate. Cold exposure (total of 1.33h at -15 degrees C) reduced population growth rate due to an elongated development period (in days), but did not affect fecundity or physiological development period (in day-degrees). Both cold and heat stress significantly reduced aphid survival. Maternal experience of heat stress reduced nymphal birth weight although nymphal development period was not affected by either cold or heat stress. The results suggest that including the effects of fluctuating, extreme temperature events on aphid life history in population forecast models is likely to be of great importance to pest management decision-making. The demonstration of maternal effects on birth weight also suggests that cross-generational effects of heat waves on population growth rates could occur.