Lethal and Sub-Lethal Effects of Nomuraea rileyi on Larval Development and Adult Fitness of Helicoverpa armigera

Abstract

The cotton bollworm, Helicoverpa armigera, is a highly polyphagous pest causing severe yield losses in several agricultural crops, and biological control using entomopathogenic fungi offers a sustainable alternative to chemical insecticides. The present study evaluates the lethal and sub-lethal effects of Nomuraea rileyi on larval development and adult fitness of H. armigera. Larvae were exposed to different conidial concentrations of N. rileyi, and mortality, developmental duration, pupation rate, and adult emergence were recorded. Results showed significant dose-dependent mortality, with higher concentrations causing rapid larval death and reduced survival rates. Sub-lethal exposure resulted in prolonged larval and pupal developmental periods, reduced pupal weight, and decreased successful adult emergence. Adult fitness parameters, including longevity, fecundity, and reproductive output, were significantly impaired in individuals that survived fungal exposure during larval stages. Infected larvae exhibited characteristic mycosis symptoms, and fungal sporulation on cadavers confirmed successful infection and pathogen development. The study also demonstrated that even surviving individuals from treated groups showed reduced physiological performance, indicating strong carryover effects of fungal infection. Environmental conditions such as moderate temperature and high humidity enhanced fungal infectivity and overall pathogenic efficiency. The findings highlight both immediate mortality and long-term fitness costs imposed by N. rileyi on H. armigera populations. Overall, the results demonstrate the strong biocontrol potential of N. rileyi as an eco-friendly alternative for managing H. armigera, with both lethal and sub-lethal effects contributing to population suppression. These findings support the integration of entomopathogenic fungi into sustainable pest management strategies in agricultural systems.