Comparative efficacy of nucleopolyhedrovirus (NPV) alone and in conjunction with chemical insecticides against fall armyworm, Spodoptera frugiperda (J. E. Smith) (Noctuidae: Lepidoptera) under laboratory conditions

The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Noctuidae: Lepidoptera), is one of the most damaging pest affecting a variety of crops, especially maize. Insecticides are the primary tool for controlling S. frugiperda in corn, but when used indiscriminately, they pollute the environment. This study investigated the compatibility of a nucleopolyhedrovirus (NPV) with selected insecticides against S. frugiperda under laboratory conditions. The insect culture was initiated from field-collected larvae, and subsequent generations were maintained in laboratory. Four insecticides, chlorantraniliprole, emamectin benzoate, spinetoram, and cypermethrin, were applied at sublethal concentrations. NPV was isolated from infected larvae, and its concentration was determined. The combination of lethal NPV concentration (1 x 10(9) POB ml(- 1)) with sublethal spinetoram (10 ppm) exhibited synergistic effects, resulting in maximum larval mortality (86.66%). Similar synergistic effects were observed with lethal NPV concentrations, sublethal chlorantraniliprole (3 ppm), and emamectin benzoate (5 ppm). LC50 values indicated increased susceptibility of 2nd instar larvae compared to 3rd instar larvae. Combining lethal doses of NPV with sub-lethal doses of the above-mentioned insecticides showed improved efficacy compared to individual applications. The study highlights the potential of combining NPV with sublethal concentrations of insecticides, particularly spinetoram, emamectin benzoate, and chlorantraniliprole, for enhanced and sustainable control of S. frugiperda. The observed synergistic effects in these combinations present a promising strategy for effective integrated pest management.