Abstract: The cowpea weevil, Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), is the main storage pest of cowpea seeds in Iran. Using biorational insecticides instead of conventional insecticides is an appropriate alternative for controlling this pest. In this study, the lethal and sublethal effects of diatomaceous earth and spinosad against C. maculatus adults on glass surface were evaluated under laboratory conditions. The results indicated that the LC₅₀ values at 24 and 48 h after treatment were 1.47 and 0.2 g/m² for diatomaceous earth and 102.9 and 68.8 mg ai/L for spinosad, respectively. Both compounds had high acute toxicity against cowpea weevil. Sublethal effects of LC₂₀ concentration of the diatomaceous earth and spinosad against C. maculatus adults were studied by detecting biological parameters. LC₂₀ concentration of diatomaceous earth and spinosad reduced the fecundity of the pest by 71.5% and 17.2%, the egg hatching rate by 57.5% and 27.8%, and adult longevity by 74.7% and 17.1%, respectively, compared to the control. Pupal period of the insect exposed to LC²⁰ concentration of diatomaceous earth and spinosad increased by 4.8% and 2.3%, respectively, compared to the control. The sublethal effect study showed that both diatomaceous earth and spinosad negatively affected life parameters of cowpea weevil. In general, combination of lethal and sublethal effects revealed that diatomaceous earth had high potential in controlling cowpea weevil.

Key words: Callosobruchus maculatus, biorational insecticides, life parameters, lethal effects, sublethal effects