Biological Characterization of the Predominant Strains of Fall Armyworm in India with Regards to Biocontrol Agents and Pheromone

The invasion of fall armyworm (FAW) to the Eastern hemisphere poses a major challenge to the food security efforts of several nations including India. Invasive FAW population is primarily composed of two predominant strains differentiated based on the mitochondrial cytochrome c oxidase (COI) gene, known as COI-RS (hybrid strain) and COI-CS (corn strain). COI-RS, in particular was found to be different from the ancestral rice strain in America and displayed characteristics of typical inter-strain hybrid population. Although the ancestral populations have been tested for their mating behaviour and response toward pheromones and biocontrol agents, similar studies have not been performed on the invasive populations. We report here the inter-strain mating behaviour of COI-RS and COI-CS populations from India along with their susceptibilities towards different biocontrol agents. COI-RS larvae were more susceptible to SpfrNPV infection compared to COI-CS larvae. The response towards other biocontrol agents was similar in the two strains. Electroantennogram res­ponse study revealed that the two strains differed in their response towards FAW pheromone, where COI-CS males displayed higher mean antennal response towards Z-9-tetradecenyl acetate (87%), Z-11-hexadecenyl acetate (12.5%) and Z-7-dodecenyl acetate (0.5%) than COI-RS males. Similar to the ancestral population, we found unidirectional mating between COI-RS females and COI-CS males while the reverse cross did not yield viable offspring. However, further detailed studies are required to confirm this observation.