Sub-lethal concentrations of the entomopathogenic fungus, Beauveria bassiana increase fitness costs of Helicoverpa armigera (Lepidoptera: Noctuidae) offspring.

Abstract

We assessed the effects of exposure of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) larvae to the entomopathogenic fungus Beauveria bassiana (isolate DC2) on life history parameters of the subsequent generation. Mortality assays against second instar larvae showed B. bassiana isolates to be significantly virulent, causing high mortality. Life history parameters such as developmental time, fecundity and survivorship were affected in the offspring of survivors of exposure to LC25 and LC50 concentrations of B. bassiana DC2. Pre-adult duration of H. armigera was significantly extended and total longevity and female progeny fecundity were decreased. Oviposition duration was shortened compared to offspring of untreated controls. All population parameters including intrinsic (r) and finite (λ) rates of increase and net (R0) and gross (GRR) reproductive rates were significantly decreased in offspring derived from H. armigera larvae treated with B. bassiana DC2. The intrinsic rate of increase (r) was 0.198 d-1, 0.120 d-1 and 0.111 d-1, respectively, for the F1 generation of controls (untreated), LC25- and LC50-treated cotton bollworm. The morphogenetic effects of B. bassiana observed due to the indirect effect of sub-lethal concentrations included abnormal pupae and adults and mortality resulted from the malformations. Pupal weight was reduced in offspring of treated individuals but sex ratios did not differ. Our results revealed that B. bassiana increased fitness costs of H. armigera in both direct (mortality) and indirect (disruption of normal development) ways. Adverse effects of sub-lethal fungal treatments on the parent generation carried over to the next generation.