Abstract: The effects of meal size and temperature on the detectable period of Sitobion avenae (Fabricius) in Adonia variegata (Goeze) were studied using a monoclonal antibody based indirect enzyme-linked-immunosorbent assay (ELISA), which can be used to evaluate the control effects of predatory natural enemies on S. avenae in wheat fields. The results showed that the curves of the middle decayed product of S. avenae in the gut of the predator, A. variegata, exhibited single peak modes at different temperatures and meal sizes. Temperature had a significant effect on the prey detectable period. With temperature increasing, the prey detectable period decreased. Especially when temperature was up to 30℃，the decay rate of prey increased sharply and the detectable period was very short, only 1.18 day. Meal size also affected the prey detectable period remarkably. While the number of preys consumed by the predators increased from one aphid to three aphids, the prey detectable period increased from 2.80 to 4.25 days at 25℃

Key words: Sitobion avenae, Adonia variegata, enzyme-linked-immunosorbent assay (ELISA), detect able period, meal size, temperature