DIFFERENT RESPONSES TO TEMPERATURE IN 3 CLOSELY-RELATED SYMPATRIC CEREAL APHIDS

Chromosomal races of the aphid Sitobion miscanthi (Takahashi), and a c losely-related species S. near fragariae (Aphididae: Macrosiphini) sho w seasonal differences in abundance in eastern Australia. We tested wh ether this was related to differences in temperature response, using c ontrolled laboratory conditions. Intrinsic rate of increase, tau(m), m ean relative growth rate (MRGR), and longevity were compared at differ ent temperatures, and rates of increase were compared outdoors under a mbient conditions. Using laboratory data, we simulated population grow th, for comparison with outdoor populations. There were significant di fferences in responses to temperature regimes both in the laboratory a nd outdoors. Outdoor populations fell well short of predicted sizes. S . miscanthi (2n = 18) showed evidence of adaptation to warmer conditio ns. In contrast, S. nr fragariae showed consistent evidence for adapta tion to cooler conditions, and S. miscanthi 2n = 17 was approximately intermediate. These data indicate that temperature responses are impor tant in the ecology, evolution and pest status of S. miscanthi clones and S. nr fragariae in Australia.