Optimization of production of nucleopolyhedrovirus ofHelicoverpa armigera throughout larval stages

Studies were carried out to optimize production of nucleopolyhedrovirus of American bollworm,Helicoverpa armigera (Hübner), by treating larvae individually with an inoculum dose that allowed maximal larval growth and also gave the highest occlusion bodies (OB) yield/larva. The maximum virus yield of 12.2x 10⁹ OB/larva was obtained when 6-day-old larvae were fed individually with a dose of 1 x 10³ OB. Topical spiracular treatment of larvae as old as 8 days with 10 μ of 2x 10⁷ OB ml^-1 gave the highest yield, of 15.2x 10⁹ OB from 13-day-old larvae, of 12.8x 10⁸ OB from prepupae and of 1.49x 10⁸ OB from pupae at the time of their death. These studies showed that dietary inoculum is the best route for 6-day-old larvae and topical spiracular treatment is the best for 8-day-old larvae.