House fly (Musca domestica L.) management in poultry production using fungal biopesticides

House flies, Musca domestica L., are economically and medically important insect pests in poultry production facilities. Standard, chemical pesticide-based control options for flies are becoming increasingly difficult due to insecticide resistance and regulatory constraints. Biopesticides based on naturally occurring fungal pathogens could provide an alternative tool for integrated pest management (IPM) in poultry production. Here we addressed several issues related to field application, persistence and performance of fungal biopesticides against flies. We demonstrated that residual spray treatments of fungal biopesticides, Beauveria bassiana and Metarhizium anisopliae could sustainably suppress fly populations through lethal and sub-lethal impacts on reproductive output. The study developed a cost-effective field delivery system whereby teneral adult flies are targeted via the application of oil-formulated spores to the lower portions of basement walls where flies momentarily rest to harden themselves following emergence. We also evaluated inexpensive, non-toxic contractor-grade plastic sheets as potential wall covering materials to support long-term spore viability. The infectivity of oil-formulated B. bassiana against flies on typical structural substrates of the poultry houses including plastic sheets declined rapidly within one or two weeks following repeated fly exposures. In further laboratory bioassays, conidia viability and enumeration tests demonstrated that flies reduced fungal persistence and infectivity through deactivation and physical removal of conidia, with higher fly densities and greater cumulative exposure hastening the decline. Nonetheless, flies' detrimental effects were substantially reduced at realistic (lower) densities and overall fungal efficacy was only marginally affected since very low densities of viable conidia were still able to cause rapid mortality, suggesting the potential for relatively long re-treatment intervals to achieve fly control. Fungal spray treatments remained viable for up to 13 weeks under laboratory conditions and periodic exposure of flies to the spray residue showed high levels mortality, with very little decline in mortality rate over time. Equivalent treatments placed in a commercial poultry house showed much more rapid decline. One trial at the end of summer showed conidia to remain viable up to seven weeks. However, repeats during the winter months revealed spore decay in one to two weeks, with fly mortality rates influenced accordingly. The exact reasons for the more rapid decay remain unclear but could be linked to high concentrations of ammonia in the basement areas, especially during winter when ventilation is minimal. While the rapid spore decay poses a challenge for operational use, our laboratory and field experimental results suggest the potential for adaptive treatment regimes with weekly spray intervals in conditions with very high fly populations and/or high ammonia levels, and potentially monthly spray intervals when fly populations and ammonia levels are reduced. Nevertheless, careful monitoring and adjustments of current housing and manure management to improve indoor air quality and create thermally stable environments would be necessary to increase the persistence and long term efficacy of biopesticide treatments. Overall, the study contributes to wider adoption of mycopesticide products as well as promotes commercial development of other potential fungal species/isolates and contributes to the reduction of pesticide consumption in the poultry industry.