Interaction between Beauveria bassiana and Bacillus thuringiensis var. israelensis for the control of house fly larvae and adults in poultry houses.

Field trials were carried out in the poultry houses to determine if a spray formulation of Beauveria bassiana (Balsamo) Vuillemin isolate R444 would enhance the control potential of Bacillus thuringiensis var. israelensis (Bti) applied in chicken feed as a larvicide against house fly larvae and the emergence of adult house flies. The trials compared larval mortalities and adult house fly emergence that resulted from the Bti plus B. bassiana treatments with those resulting from a commercial larvicide, Larvadex, plus B. bassiana treatments. All treatments significantly reduced the house fly larval densities and adult house fly emergence compared with any of the agents acting alone. After 6 wk of application, house fly larvae decreased by 11% as a result of B. bassiana treatment alone, 41% for 250 mg.kg(-1) Bti alone, and 42% for 500 mg.kg(-1) Bti alone. Larval mortalities as a result of the combination treatments were 45 and 52% as a result of 250 mg.kg(-1) Bti plus B. bassiana and 500 mg.kg(-1) Bti plus B. bassiana treatments respectively. House fly larval mortalities as a result of Larvadex and B. bassiana were 30% for Larvadex alone and 38% as a result of Larvadex plus B. bassiana. The Bti treatments were more effective at inhibiting the emergence of adult house flies than Larvadex, even when Larvadex was applied together with B. bassiana. The interaction effects of Bti plus B. bassiana and Larvadex plus B. bassiana were additive. These trials suggested that in the control of house fly larvae, the efficacy of Bti, applied as a larvicide, may be improved with frequent spray applications of B. bassiana to the chicken manure.