Natural mortality of invasive fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in maize agroecosystems of northeast India

Abstract

Invasive fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is a pest of American origin that has recently invaded Asian countries, including India. After causing huge losses in the Africa and Asia, the FAW is now affecting large areas of India. Indigenous natural enemies of related pest species are the first defense against invasive pests and understanding their role in population suppression of invasive pests is a first step towards the development of a comprehensive management program. Therefore, we studied the natural enemy complex responsible for natural mortality of FAW in northeast India. Various locations were surveyed across five major districts of Meghalaya state, where more than 26 species of natural enemies were found attacking FAW. A total of 56.6% to 73.1% of larvae were found to be either parasitized or infected with naturally occurring entomopathogens. Species richness and diversity of predators were determined in maize fields at different locations. Values of Menhinick's species richness index (DMn) varied from 0.23 to 0.31 and Shannon-Wiener index (H) ranged from 2.16 to 2.6 across various locations. The Simpson Index (D) indicated high predator diversity in maize fields. The entomopathogenic fungus, Metarhizium rileyi (Farlow) Samson and the baculovirus, SpfrNPV were observed to be the dominant mortality factors throughout the season, responsible for >50% mortality of FAW larvae. This investigation demonstrated that indigenous natural enemies of related noctuid species can widen their host range and successfully adopt the invasive FAW as a novel host/prey in invaded regions. Therefore, conservation of such biocontrol agents could be vital for mitigating FAW damage in maize agroecosystems.