Partially purified Glycine max proteinase inhibitors: potential bioactive compounds against tobacco cutworm, Spodoptera litura (Fabricius, 1775) (Lepidoptera: Noctuidae)

Abstract

Spodoptera litura (Fabricius, 1775), a polyphagous defoliator with broad host spectrum, causes significant damage to agriculturally important crops. Serine protease is primarily responsible for most of the proteolytic activity in the larval gut of lepidopteran insects. Second-instar larvae were reared on an artificial diet containing serine trypsin inhibitor partially purified from Glycine max seeds. Different concentrations were amended in the diet, i.e. 25, 50, 100, 200, and 400 μg/mL. The larval development period, total developmental period, longevity, fecundity, larval weight, and mean relative growth rate were decreased at the 100 μg/mL concentration. However, with further increase in concentration, the above parameters were all found to increase. Nutritional indices revealed reduction in efficiency of conversion of digested food and approximate digestibility, whereas increase in efficiency of conversion of ingested food had significant influence on food assimilation. Trypsin activity was suppressed at 100 μg/mL with increase in exposure interval. Results reveal that soybean protease inhibitor inhibited S. Litura gut proteinase and it was more effective at lower concentrations. Thus, low levels of inhibitor would be enough to affect the growth and development of the target pest for the development of transgenic plants.