Effect of pyriproxyfen and diofenolan on the metamorphosis and enzymatic activities in tobacco cutworm, Spodoptera litura.

Spodoptera litura (Lepidoptera: Noctuidae) is a polyphagous pest of agricultural crops and causes severe economic loss. In the present study, the biological effect and enzymatic activity of two insect growth regulators, pyriproxyfen and diofenolan was evaluated against S. litura larva. The penultimate instar larvae (0, 24, and 48-hours old) were treated topically at the last three abdominal tergites with sublethal doses (1, 2, and 4µg/µl) of both the juvenile hormonal analogues (JHAs). Several effects were observed such as prolongation in larval-larval and larval-pupal ecdysial duration, larval and pupal mortality, eclosion failure, formation of intermediates, low pupation and reduced adult emergence. Along with these metamorphic catastrophe effects, both JHAs had inhibitory effects for acetylcholinesterase (AChE) but excitatory effects for glutathione –S-transferase enzyme (GST). Whereas, Log IC50 and IC50 values for adult emergence inhibition rate were found to be -0.98 and 0.1 µg/ µl for 24-hours old larvae (Pyriproxyfen); 0.005 and 1.01 µg/ µl for 48-hours old larvae (Pyriproxyfen); -0.085 and 0.82 µg/ µl for 24-hours old larvae (Diofenolan); -0.09 and 1.23 µg/ µl for 48-hours old larvae (Diofenolan). Our result manifests the insecticidal potency of both the IGRs against S. litura.