Author(s):

AK Sadawarte, MN Nachane MP Moharil and NS Satpute

Abstract: Helicoverpa armigera nucleo polyhedrosis virus (HaNPV) is the most promising bio-agent. However, as the age of the larvae increases, then susceptibility to HaNPV decreases. This becomes a bottleneck in its effectiveness. Present study deals with the reasons behind this decrease in efficacy. Role of phenoloxidase (PO) in age related resistance, characterization of PO was studied. Phenoloxidase activity was more in cellular fraction of hemolymph in normal larvae of H. armigera. Whereas it was high in plasma fraction of virosed larvae. Moreover its magnitude was more in 5^th instar larvae as compared to 3^rd instar larvae. The Km of PO from virosed larvae decreased in respect to normal larvae, where as the Vmax in virosed larvae increased over that of normal larvae. Dopamine was found to be the best substrate than any other studied. Enzyme PO was optically active at 40⁰C in normal larvae as well as virosed. The PO from normal and virosed larvae of H. armigera showed almost 100 % enzyme activity up to 30^oC, which decreased thereafter. Optimum pH for PO activity was found to be 9.0 for normal and virosed H. armigera larvae. Amongst all inhibitors of PO tested SDS was found to be the best followed by EGTA >PTU> EDTA > PMSF> DMSO > Garlic extract. Two PO isozymes were present in hemolymph of normal and virosed H armigera larvae.

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