Joint toxicity and control efficacy of chemical pesticides and insecticidal bacteria against Spodoptera frugiperda (Lepidoptera: Noctuidae)

Abstract

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a globally prevalent pest, posing a substantial threat to a wide range of crops. Nevertheless, the long-term and excessive application of single pesticides has led to the development of resistance to multiple pesticides in FAW. In this study, nine different combinations of two compound mixed pesticides were investigated. The combinations of Metaflumizone (MFZ) with Empedobacter brevis, and Emamectin benzoate (EMB) with Bacillus thuringiensis G033A all demonstrated significant synergistic effects in the control of FAW, with their Coefficient of Toxicity Collaboration (CTC) all surpassing 120. When the recommended dose of E. brevis was reduced by 50%, and the recommended dose of MFZ was decreased by 25%, and 50% respectively, the compound pesticides still maintained high field control efficacy against FAW (over 80% on the 7th day). Similarly, when the recommended dose of B. thuringiensis G033A was reduced by 50%, and the recommended dose of EMB was decreased by 25%, and 50%, respectively, high field control efficacy against FAW was also achieved (over 70% on the 7th day). Nevertheless, when the reduction of MFZ and EMB exceeded 75% of the recommended dose, the synergistic effect of the mixture also began to decline. Our research indicates that it is feasible to reduce the doses of both chemical pesticides and bioengineered bacteria by 50% each. The combinations of MFZ and E.brevis, as well as EMB and B. thuringiensis G033A, can be effectively applied for the control of FAW.