Efficacy of combined treatments of abamectin with three inert dusts for the control of Callosobruchus chinensis on cowpea seeds

The insecticidal efficacy of abamectin (AB) and three inert dusts, diatomaceous earth (DE), zeolite (ZE) and kaolin (KA), was evaluated alone and in binary mixtures as stored cowpea protectants against Callosobruchus chinensis. Inert dusts (DE, ZE and KA) were tested at 100, 500 and 1000 mg/kg (ppm), and abamectin was applied at 0.1, 0.25 and 0.5 mg/kg (ppm). Adult mortality of C. chinensis was evaluated after 3 and 7 days of treatment, while progeny production and cowpea seed weight loss were recorded for all tested treatments after 60 days. The mortality of adults in the binary treatments was higher than the individual treatments of inert dusts or AB. Combined treatments of AB at 0.5 mg/kg with DE, ZE or KA at 500 and 1000 mg/kg led to 100% mortality after 7 days of treatment. Moreover, combined treatments of AB (0.25 mg/kg) with KA (1000 mg/kg), AB (0.25 mg/kg) with ZE (1000 mg/kg) and AB (0.5 mg/kg) with KA (100 mg/kg) caused 100% mortality of adults after 7 days of treatment. After 3 days, the binary mixture of AB (0.5 mg/kg) with KA (1000 mg/kg) was the only treatment inducing 100% adult mortality. All treatments with inert dusts, AB, and their binary mixtures caused significant decrease in progeny production of C. chinensis after 60 days of exposure. In particular, treatments with high concentrations induced strong progeny reduction and led to complete protection of cowpea seeds against weight loss and damage caused by C. chinensis after 60 days. Furthermore, no adverse effect on germination was observed in cowpea seeds treated with the highest application rates of inert dusts, AB, and their mixtures. Our findings demonstrated that binary mixtures of inert dusts with abamectin could be successfully used as potential protectants for cowpea seeds against C. chinensis.