Reduced physiological and reproductive fitness induced by Nerium oleander leaf extracts in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

Helicoverpa armigera is one of the most devastating, cosmopolitan, polyphagous and multivoltine pests of agricultural crops. The growing side-effects of synthetic insecticides used to control agricultural pests, have amplified demand for the relatively safe and biodegradable compounds which offer benefits over synthetic chemical insecticides. Hence, the current study investigates the effects of Nerium oleander methanol leaf extracts on the physiological and reproductive fitness of H. armigera. Addition of the range of extract concentration; 0.5%–10.0%; in the larval diet induced an appreciable and dose-dependent effect on the developmental parameters of H. armigera. The extract, though resulted in moderate larval and pupal mortality, caused significant growth regulatory effects. A prolonged larval duration, formation of larval-pupal intermediates and significant reduction in the average larval weight gain by 26.5% - 63.4%; and pupal weight by 23.9% - 63.4% was recorded. The 74.6% to 54.9% reduction in the oviposition duration in the emerged adults, and diminished fecundity and egg hatch in the corresponding range of 0.78–0.63 and 0.89–0.62 demonstrated negative impact of the extract on the adult reproductive fitness. The adverse impact of N. oleander methanol leaf extracts on the growth and development of H. armigera leading to the reproductive disadvantage in adults can be beneficial in the field management; though its use can only be ascertained after identification of bioactive constituents and elucidating their mode of action.