Effect of dietary stress of emamectin benzoate on the fitness cost of American bollworm, Helicoverpa armigera (Hübner, 1808)

Abstract

Present study assessed the effect of Emamectin benzoate (EMB) on the survival, growth and nutrition efficiency of Helicoverpa armigera. Dietary EMB exhibited a significant systemic toxicity in H. armigera larvae resulting in LD50 and LD90 value of 0.092 µg/mL and 0.156 µg/mL, respectively. Feeding with 0.05–0.2 µg/mL EMB caused 10–100% larval mortality in a dose-dependent manner. Feeding the IV instars of H. armigera with 0.1–1.6 µg/mL EMB-incorporated diet deterred feeding significantly. Substantial deterrent effects of EMB with lower LD50 values indicate the noteworthy systemic toxicity of EMB on the H. armigera larvae. Both choice and no-choice bioassay with dietary EMB showed a distinct preference of larvae towards control diet. Feeding the larvae with sublethal doses of 0.05 − 0.01 µg/mL EMB impaired ingestion and digestion, and induced considerable post-ingestive toxicity in larvae. Relative Consumption Rate (RCR) and the Relative Growth Rate (RGR) were recorded in the range of 1.653–3.985 and 0.385–0.978, respectively. The nutrition indices of larvae revealed reduction in Efficiency of Conversion of Ingested Food (ECI) by 10–24% and Efficiency of Conversion of Digested Food (ECD) by 2.0–52% and in Approximate Digestibility (AD) by 09–63%. The noticeable decrease in the food utilization, digestion and assimilation may have resulted in the observed reduced larval growth. The decreased metabolic efficiency in H. armigera larvae implicated that dietary EMB probably weakened the biochemical machinery of larval gut and reduced physiological fitness. The results suggest that use of EMB can be an effective tool in Integrated Pest Management program of H. armigera.