Variations in the susceptibility of Indian populations of the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae) to selected insecticides

The fall armyworm, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae), is a new invasive species in India. This pest is occurring in serious proportions, causing significant damage to the maize crop in several states of India. Insecticides are sprayed regularly for the control of fall armyworm that could lead to the development of resistance. Hence, we measured the levels of susceptibility to insecticides among different populations of fall armyworm in India. The median lethal concentrations (LC 50 value) were estimated through leaf dip bioassays using third instar larvae for various conventional and newer insecticide molecules. The lowest LC 50 values were recorded on emamectin benzoate(0.11-0.12 ppm) and highest LC 50 values was recorded on chlorpyrifos (99.73-106.32 ppm). This study suggested that emamectin benzoate was relatively more toxic and chlorpyrifos was less toxic to the fall armyworm. Differences in LC 50 values for a given insecticide across populations was non-significant, suggesting the occurrence of similar populations in South India. Results of this study throw light on current levels of susceptibility prevailing in S. frugiperda for various insecticides and may form a basis for monitoring the development of resistance in S. frugiperda in India.