Does Recently Invaded Fall Armyworm, Spodoptera frugiperda Displace Native Lepidopteran Pests of Maize in India?

Competitions are common among interacting species for resources or space. In India, recently invaded fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) has to compete with native lepidopterans to become successful in an exotic environment. Invasive FAW and native pink stem borer (PSB), Sesamia inferens belong to the same feeding guild, and hence they are intraguild competitors. FAW is an aggressive pest and is known to have a cannibalism/predation habit and hence a good model system to study the ecological interactions. The present study examined the incidence of different lepidopteran pests in maize fields for three years after the recent invasion. Incidence of FAW increased over the years compared to other lepidopteran pests. Laboratory and field intraguild competition studies were conducted to understand the survival and fitness of FAW and PSB larvae under different competition scenarios. Our study demonstrated that survival of FAW was reduced in intraspecific as compared to interspecific competition. However, survival of PSB was significantly reduced in interspecific competition due to intraguild predation by FAW. Fitness cost analysis of PSB pupae survived in competition with FAW larvae indicated that they were negatively affected with reduced pupal weight. Low field incidence of PSB and its lowest survival in the presence of intraguild competitor, i.e. FAW prove that PSB might get displaced from the maize ecosystem in the near future.