The effect of oxindole and biological insecticide Biolep®on toxicity, feeding indices, digestive enzymes and energy reserves of American cotton bollworm, Helicoverpa armigera Hubner (Lep.: Noctuidae)

Oxindole is an inhibitor of the eicosanoid signal leading to inhibiting the immune system of insects. One of the important problems of using biological agents such as Bacillus thuringiensis Kurstaki (BtK) is their low efficiency and slowness of effect. In this research, the effect of oxindole and Biolep® based on BtK, were investigated on toxicity, feeding indices, energy reserves, and digestive enzyme activity of Helicoverpa armigera Hubner (Lep.: Noctuidae) larvae. The results showed that oxindole increased larval mortality and decreased LC50 and LT50 values of Biolep®. The feeding indices of cotton bollworm were changed under the influence of sub-lethal concentrations of bacteria and oxindole. At the concentration of 0.5 g oxindole/ kg diet the relative growth rate (RGR) decreased and the approximate digestibility (AD%) increased compared to the absence of oxindole. The use of oxindole along with bacteria also decreased lipase activity. Glycogen as an energy reserve was adversely affected by simultaneous application of oxindole concentrations of 0.1 or 0.5 g.kg-1 and the sub-lethal concentrations of Biolep® compared to sub-lethal concentrations of Biolep® only. The results of this research showed that by adding oxindole as an inhibitor of eicosanoid signal and immune system to the diet of cotton bollworm, the effectiveness of Biolap® increased and the feeding physiology of the pest was affected.