The influence of temperature and photoperiod changes on the Nearctic cereal aphid parasitoid Aphelinus nigritus (Howard)

Aphelinus nigritus (Howard) is a Nearctic solitary aphid parasitoid found in the Great Plains of the United States. It attacks cereal aphids during warm summer and fall months, but little is known about its life history. This study aims to describe degree day accumulation requirements for development and possible overwintering strategies of A. nigritus. Two replicated experiments were initiated to investigate whether A. nigritus is triggered to enter diapause following changes in environmental conditions. In the first experiment, we isolated the effects of changing light cycles and typical temperature fluctuations on newly emerged adults, while in the second experiment we isolated these effects on parasitoid larvae within aphids. Typical temperature fluctuations simulated summer and fall conditions in Oklahoma:  24-28ºC and 10-14ºC daily fluctuations respectively, each at 15:9 L:D, 12:12 L:D and 9:15 L:D.  Available data reveal that when emerging adults and their subsequently parasitized hosts were exposed to warm temperature fluctuations, developmental times were similar among day lengths.  Developmental times were also similar among warm temperature treatments when parasitoid mummies were exposed to variable day lengths.  However, no-to-low emergence rates at the low temperature and shortest daylength are preventing comparisons of developmental times; mummies remain under observation for emergence.  These findings indicate that environmental changes during the early/mid-instar parasitoid life stage for A. nigritus can influence development.