Immunological and antioxidant responses of larval Helicoverpa armigera (Lepidoptera: Noctuidae) to gibberellic acid in the diet

Gibberellic acid (GA3) is usually used as a plant growth regulator to enhance the quality and quantity of crop yield. Moreover, GA3 may also affect insects and other herbivores that rely on a particular plant for their living. Hence, in the present study the defensive mechanisms of Helicoverpa armigera (Hubner) fed on the diet contating GA3 have been considered. The larvae fed with GA3 significantly exhibited cellular and humoral inhibitory responses such as, reduced nodule formation and phenoloxidase activity. Antioxidant system was also affected; the lowest activity of peroxidase, catalase, superoxide dismutase, ascorbate peroxidise, glucose-6-phosphate dehydrogenase, and glutathione S-transferases was observed in control larvae while the highest activity was found in those larvae that were provided with a diet containing 800 mu g/g GA3. The metabolites like triglyceride, glycogen, and cholesterol were reduced compared to the control. It is concluded that the use of plant growth regulators like GA3 not only does benefit plants for their growth and yield, but also can somehow help plants to withstand the impact of herbivores. Hence, studies covering direct field collected insects from crop plants treated with PGRs would be beneficial for further studies.