Monoterpenes improve the insecticidal efficacy of spinosad against Sitophilus oryzae (L.) on stored wheat

Abstract

Combination of crop protectants is an important approach to increase insecticidal efficacy and reduce the application rates. In this study, the insecticidal efficacy of spinosad and seven monoterpenes, alone and in binary combinations, was evaluated against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) in stored wheat. Spinosad was tested at application rates of 0.1 and 0.5 mg/kg while monoterpenes were tested at 0.5, 1.0 and 2.0 g/kg. Mortality of adults after 7, 14 and 21 days, progeny reduction after 45 and 90 days, and grain weight loss were recorded for all treatments. The results showed that the complete mortality (100.0%) of S. oryzae adults was observed in wheat treated with 0.5 mg/kg of spinosad + 2.0 g/kg of carvone or P-cymene or menthone after 21 days. At the same time, no progeny of S. oryzae was resulted in the combined treatments (0.5 mg/kg of spinosad + 2.0 g/kg of carvone or 0.5 mg/kg of spinosad + 2.0 g/kg of P-cymene) after 45 and 90 days. The same trends were observed for grains weight loss as the binary treatments at highest application rates preserved the wheat seeds free from damage caused by S. oryzae for 90 days.