Synergistic effect of fumigation with ethyl formate and methyl salicylate on mortality of life stages of adzuki bean beetle, Callosobruchus chinensis (L.)

Abstract Ethyl formate (EF) is becoming an insecticide of choice for protecting stored commodities. Along with EF, methyl salicylate (MS) is also naturally occurring, and both are generally regarded as safe fumigants for their higher threshold limit values (TLV) and residual status below minimum residue limit (MRL). Sub-lethal doses of EF and MS were evaluated to determine if there was a synergistic effect on fumigation against life stages of the adzuki bean beetle, Callosobruchus chinensis (L.) infesting adzuki bean grains. Based on lethal dose (LD) values, the C. chinensis eggs and adults were equally susceptible to EF followed by larvae and pupae. Adults were the most MS-sensitive followed by eggs and larvae, and pupae were the most tolerant stage. The mortalities of all the life stages of C. chinensis by combined fumigation with sub-lethal EF and MS doses were significantly higher compared to the sum of their separate fumigations revealing a notable synergistic effect. Moreover, the maximum doses of EF and MS tested for synergistic fumigation test did not hamper the germination potential of adzuki been seeds. The synergistic effect between EF and MS can significantly reduce the dose rate of flammable EF against C. chinensis thereby offering a good prospect for EF + MS formulation as an alternative to safeguard stored adzuki bean.