Antifeedant and cytotoxic activity of gibberellic acid against Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae)

The present study investigates the effect of gibberellic acid (GA3), a terpenoid and phytohormone, on the digestive physiology and intermediary metabolism of the cotton bollworm Helicoverpa armigera Hubner (Lepidoptera, Noctuidae). Incorporation of GA3 (800 mu g g(-1) diet) in an artificial diet results in significant reductions in the rates of diet consumption and the efficiency of conversion of food consumption by by H. armigera larvae. The relative growth rate decreases as the concentration increases. The relative alpha-amylase activity in sixth-instar larvae of H. armigera decreases significantly after ingestion of four concentrations of GA3. Histological studies of the midgut in GA3-treated larvae (800 mu g g(-1) diet) show degeneration of the epithelial cells. The alanine and aspartate aminotransferase activity decreases at the highest concentration. However, acid phosphatase, alkaline phosphatase, gamma-glutamyl transferase and lactate dehydrogenase activity increase significantly compared with the control. The results clearly demonstrate the adverse effects of GA3 on H. armigera via interruption of nutritional physiology and metabolism.