Laboratory and Field Evaluation of Bacillus thuringiensis Berlinger var Kurstaki, on African Bollworm (Helicoverpa armigera, Hubner)

Laboratory and field testing of Delfin, a water dispersible micro granule containing Bacillus thuringiensis (Bt) was carried out to see its efficacy against African Bollworm (Helicoverpa armigera) on haricot bean at Melka Werer between June 1990 and September 1991. In the laboratory, a factorial experiment (CRD in 3 replication) with four rates of the product (0.00, 1.50, 1.75 and 2.00 kg/ha) at five developmental stages (eggs to 4th instar larvae) of the insect was carried out. Molasses (2 1/ha) were added to each Bt treatment to serve as a sticker and feeding initiator. Haricot bean leaves or green pods were dipped in the Bt preparation and placed in the petridishes continuing the insect at different developmental stages. In the field experiment, the different rates of Bt preparation and endosulfan 35 percent EC (2 1/ha) were evaluated under controlled (plants in synthetic cloth cages) and natural (uncontrolled) field condition in RCBD with 4 replication. The different stages of the insect were introduced to the crop (haricot bean variety Ex. Rico 23) at flowering stages and after about 24 hours the different Bt preparation + molasses or endosulfan were sprayed. Laboratory results indicated that Bt treatments were significantly different from the check and larval mortality increased with increased rate of Bt applications. Effective control of ABW was achieved when Bt at the rate of 1.50 kg/ha was applied on 1st and 2nd instar larvae with average mortality of 99.6 percent and 90.8 percent respectively. Results of field testing also revealed that differences in larval mortality between treated and untreated plots were significant and all treated plots rendered better grain yields than the untreated ones. Bt was also equally effective as endosulfan in the control of early instars of ABW. However, its impact on other harmful or beneficial insects was unclear and its use in combination with synthetic chemicals remains subject to further investigations.