Sublethal effects of diazinon, fenitrothion and chlorpyrifos on the functional response of predatory bug, Andrallus spinidens Fabricius (Hem.: Pentatomidae) in the laboratory conditions

The sublethal effects of diazinon, fenitrothion and chlorpyrifos on the functional response of predatory bug, Andrallus spinidens Fabricius (Hem.: Pentatomidae), a potential biological control agent, were studied on 5th-instar nymphs. The experiment was conducted in varying densities (2, 4, 8, 16, 32 and 64) of last instars larvae of Chilo suppressalis Walker (Lepidoptera: Pyralidae) as prey at 25 ± 2 °C, 60% ± 10% relative humidity (RH) and a photoperiod of 16:8 h (L: D). The results of logistic regressions revealed a type II functional response in the control and all insecticide treatments. Comparison of functional response curves revealed that tested insecticides markedly decreased the mean of preys consumed by A. spinidens. Among them, functional response curve of A. spinidens in chlorpyrifos treatment was significantly lower than the other treatments. In this study, application of insecticides caused a decrease in the attack rate and an increase in the handling time of exposed bugs compared with the control. The longest handling time (3.97 ± 0.62) and the lowest attack rate (0.023 ± 0.007) were observed in chlorpyrifos and fenitrothion treatments, respectively. The results suggested that the adverse effect of these insecticides on A. spinidens should be considered in integrated pest management programs (IPM).