Different thermal responses in two coexisting aphids may account for differences in their seasonal abundance in cotton fields

The coexistence of species competing for resources can be facilitated by differential effects of temperature on fitness components. The coexisting cotton aphids Aphis gossypii Glover and Acyrthosiphon gossypii Mordvilko show seasonal differences in abundance in North-Western China, the former reaching higher field abundances and declining later in the season than the latter. We hypothesized that differences in responses to temperature might be the proximate mechanism driving this difference in population dynamics between the two species. Aphids from laboratory-reared colonies and directly collected from the field in early summer were used to study their development, survival and reproduction under a range of constant temperatures. Life-table parameters suggest that A. gossypii performed better than Ac. gossypii under all temperature treatments tested, and the difference tended to be strongest under high temperatures. These observations are consistent with the higher numbers and the later decline of A. gossypii in the field compared with Ac. gossypii. Our findings help in understanding the seasonal population dynamics of both species, as well as in forecasting pest trends under global warming scenarios.