ABSTRACT

Suspensions containing Bacillus thuringiensis (B.t.) and Bacillus polymyxa (B.p.) were evaluated as microbial control agents against American bollworm (ABW) Heliothis armigera larvae. Latent effects on pupae formation, adult emergence, fecundity and fertility were also investigated. Significant mortality was obtained three days after feeding larvae on treated diet with the tested pathogens. Average weight of pupae formed in the bacterial treatments significantly reduced compared to the control. Mean percentage of adult emergence from pupae treated in the larval stage was significantly less in the bacterial treatments than in the control. Emerged adults lost their normal ability for laying viable eggs particularly when the highest concentration was tested against 2^nd instar larvae. All the effects were concentration, instar and strain dependent. Great effect was obtained when younger larvae fed for three days on treated diet with 107 (cell/ml) from any of the two tested pathogens. In general, the B. t. strain was more potent for killing larvae, inhibiting pupation and emergence of H. armigera than the B.p. strain in all treatments. However, the contrast was evident when their effects on adult fecundity and fertility were considered. The ^2nd instar larvae were more sensitive to both strains of B.t. and B.p. than the 4^th instar larvae.