Preparation and Application of Biocontrol Formulation of Housefly—Entomopathogenic Fungus—Metarhizium brunneum

Utilizing entomopathogenic fungi as a biological control method for parasitic houseflies in livestock presents a promising and innovative alternative. This study aimed to evaluate the control efficacy of a lyophilized <i>Metarhizium brunneum</i> preparation, both alone and in combination with the insecticide low-dose deltamethrin, to control houseflies in Hu sheep on a farm based in Gansu Province, northwestern China. The experimental design included four groups: <i>M. brunneum</i> wettable powder (WP) treatment group, <i>M. brunneum</i> + deltamethrin combination WP treatment group, deltamethrin group, and a control group. By observing the mortality rate of houseflies at 1, 3, 5, and 7 days post-treatment, the data were analyzed, and control efficacy was calculated to evaluate the effectiveness of each treatment group on houseflies at different time points. On day 7, the combination of WP with deltamethrin resulted in 79.2% control of housefly larvae and pupae and 85.42% control of adult houseflies, respectively, surpassing the efficacy observed in the deltamethrin-only group. The incorporation of low-dose insecticides into the fungal treatment increased the mortality rate by 17.1% compared to the use of <i>M. brunneum</i> alone, significantly reducing the overall pesticide usage while enhancing the efficacy of biological control.