Combined effect of biopesticides on the digestive enzymatic profiles of Cnaphalocrocis medinalis (Guenée) (the rice leaffolder) (Insecta: Lepidoptera: Pyralidae).

Plant extracts, especially botanical insecticides, are currently studied more and more because of the possibility of their use in plant protection. Many of the natural plant compounds and organic compounds used in the control of insect pests are known to affect digestive enzymes. When fed a diet of rice leaves treated with botanical insecticides and bacterial toxins in bioassays, activities of the digestive enzymes protease, amylase, and lipase in the rice leaffolder larvae are affected. Digestive enzyme activities were affected by botanical insecticides and bacterial toxins individually and in combination. When combined, the effect was more severe at low concentration. There were statistically significant differences (P < or = 0.05) in enzyme activities in combined and individual treatments. The combination of Btk and botanical insecticides caused a two-fold decrease in enzyme activity even at reduced concentration. Clear dose-response relationships were established with respect to enzyme activity. A synergistic effect of botanical insecticides and bacterial toxins was found when combined in low doses. These effects are most pronounced in early instars.