Long term efficacy of three chitin synthesis inhibitors and oxymatrine as cowpea seed protectants against Callosobruchus maculatus and Callosobruchus chinensis

Abstract

The residual efficacy of three chitin synthesis inhibitors (CSIs) (chlorfluazuron, hexaflumuron and lufenuron) and oxymatrine at an application rate of 5.0 mg/kg was evaluated against Callosobruchus maculatus and Callosobruchus chinensis monthly for 5 consecutive months (6 bioassays). In each bioassay, the mortality of two insect adults was counted after 7 days, progeny reduction and cowpea weight loss percentages were recorded after 45 days. Our results revealed that CSIs caused high level of adult mortality of both insects and oxymatrine caused a complete adult mortality (100%) for five months storage. The tested CSIs produced a significant progeny reduction of C. maculatus and C. chinensis but did not achieve a complete reduction of F1 progeny during all storage periods. A complete progeny suppression of two insects and full cowpea seed protection were observed in all oxymatrine treatments during the entire storage periods. A remarkable protection of cowpea seeds was also achieved in the treatments with CSIs particularly chlorfluazuron during the first 3 months. These findings indicate CSIs and oxymatrine could be implemented in IPM of these insects.