Persistence and efficacy of a Beauveria bassiana biopesticide against the house fly, Musca domestica, on typical structural substrates of poultry houses

Entomopathogenic fungi, such as Beauveria bassiana, offer potential for use as biopesticides for control of house flies in poultry production facilities. This study evaluates persistence and efficacy of oil-formulated B. bassiana conidia against adult house flies on a range of structural substrates commonly found in poultry houses. Exposure of flies to fungal-treated surfaces produced high levels of infection leading up to 100% mortality in 6–10 days. However, the infectivity of the spray residues declined rapidly within 1 or 2 weeks following repeated fly exposures. Investigations showed that, in the absence of flies, conidia remained viable on test surfaces for up to 3 months regardless of substrate type, application method or fungal production batch. Rather, it was the presence of flies themselves that was responsible for reducing persistence. The exact mechanisms remain unclear but involve a combination of physical removal and chemical deactivation, with decay rates increasing at higher fly densities. While the rapid decay could pose a challenge for operational use, the results suggest it might be possible to tailor treatment frequencies to fly densities with, for example, weekly applications at high fly densities and longer intervals when populations decline. Further research is needed to determine persistence in semifield and field settings and to quantify the influence of fly densities under natural exposure conditions.