Department of Agricultural Entomology, Agricultural College and Research Institute, Madurai-625 104, Tamil Nadu (India).
Fourth and fifth larval instars of Spodoptera litura (Fabricius) were treated with 10 per cent aqueous extract of Tribulus terrestris L. to study its influence on larval biomass and virus yield produced in vivo. Larvae were inoculated with NPV at 1 x 108 PIBs/ml through castor leaves, using three methods, viz, NPV simultaneously with T. terrestris, and 24 h later, and earlier to T. terrestris treatment and compared with NPV alone. Virus yield was recorded eight days after virus inoculation. Larvae treated with NPV along with T. terrestris extract simultaneously and 24 h later with T. terrestris weighed significantly more than the remaining treatments and also yielded maximum quantity of occluded bodies of 5.226 ± 0.463 and 5.182 ± 0.416 x 109 PIBs/g of larvae (1.59 and 1.58 -fold) for the 4th instar; and 5.377 ± 0.629 and 5.525 ± 0.541 x 109 PIBs/g of larvae (1.64 and 1.70-fold) for the 5th instar, respectively, when compared with larvae treated with NPV alone and 24 h earlier with T. terrestris extract. Size of the 4th and 5th instar larvae had positive relationship with the yield of NPV in vivo. But the weight of 5th instar larvae showed no correlation with the yield of NPV.
