Insecticidal, genotoxic and biochemical effects of Shewanella sp. (SS4) and Thauera sp. (M9) on Spodoptera litura.

Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) is a polyphagous pest causing economic losses to a number of agricultural crops. The present study was conducted to explore the insecticidal potential of some soil bacteria against S. litura. Among the tested bacterial isolates, Shewanella sp. (SS4) and Thauera sp. (M9) caused higher larval mortality. Concentration–response bioassays indicated a dose‐dependent increase in larval mortality with maximum mortality of 80 and 76%, respectively, due to Shewanella sp. and Thauera sp. Both the bacteria negatively affected the growth and development, reduced adult emergence and induced morphological deformities in adults. Nutritional parameters of S. litura i.e. relative growth and consumption rate, efficiency of conversion of ingested and digested food as well as approximate digestibility of food decreased with increasing bacterial concentrations. Histopathological studies revealed the disruption of peritrophic membrane and midgut epithelium of larvae. Profiles of digestive enzymes i.e. α‐amylases, α, β‐glucosidases and galactosidases, lipases and proteases were also significantly decreased with bacterial treatment. Comet assay test indicated DNA damage in larval haemocytes due to bacterial infection. These results imply that both these bacterial isolates have the potential as biological control agents and may prove as environmentally friendly alternative for pest management techniques. [ABSTRACT FROM AUTHOR]