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House flies (Musca domesticaL.) (Diptera: Muscidae) are challenging pests to control. Biological control using Carcinops pumiliobeetles may help to reduce house fly populations. However, it is unknown if C. pumiliobeetles are compatible with Beauveria bassiana, another house fly biological control option. Five strains of commercially available (GHA, HF23, and L90) and newly discovered (NFH10 and PSU1) strains of B. bassianawere used to test the comparative susceptibility of adult house flies and adult C. pumiliousing different laboratory exposure methods. Adult house flies were susceptible to B. bassianain contact filter paper assays (89%–98% mortality) and immersion assays (100% mortality) at the same 108conidia suspension using 0.1% CapSil as an aqueous surfactant. Carcinops pumiliowere less susceptible than flies to B. bassianainfection using the contact and immersion assays at the same 108conidial concentration, with 4.4%–12.2% and 8.3%–24.6% mortality, respectively. Immersion in an aqueous conidial suspension resulted in higher mortality compared to contact with treated filter papers at the same 108concentration with house flies and beetles. We conclude that C. pumiliocan safely be used as a biological control agent for house flies with B. bassianain animal production systems.

House fly (Musca domesticaL.) (Diptera: Muscidae) populations can negatively impact poultry layer facilities, posing a risk to human and animal health and egg food safety. House flies quickly develop resistance to traditional chemical control methods; therefore, improved biological control may provide opportunities for improved integrated pest management (IPM) programs. Biological control methods currently used include augmentative releases of pteromalid pupal parasitoids and application of the fungal entomopathogen Beauveria bassiana(Balsamo) Vuillemin. This study used bioassays to compare the impact of different B. bassianastrains on survival of house flies and of 3 species of filth fly parasitoids. The B. bassianathat were compared were 3 new field-collected isolates, an older field-collected isolate (L90), and a common commercially available strain (GHA). Flies and parasitoids were exposed to filter paper treated with 1.5 × 109spores of each strain and a control. All field-isolated strains induced lower mean survival times in house flies than GHA did. The results for all species of parasitoids demonstrated less difference among the treatment groups and the control than in-house flies. Although there was some effect of B. bassianaexposure on parasitoid mortality, the expected spatial separation of parasitoids from areas of application may offer some protection. Using the most effective tested strains of B. bassianaand filth fly parasitoids jointly could be a biological component of an IPM plan for fly control in poultry facilities.