Activity of native and commercial strains of Metarhizium spp. against the poultry red mite Dermanyssus gallinae under different environmental conditions

The poultry red mite (PRM), Dermanyssus gallinae, is a major pest of laying hens with extremely limited control means. To evaluate the potential of natural and commercial entomopathogenic fungi (EPF) for use against D. gallinae, we tested four wild populations of D. gallinae from Israeli farms. The genus Aspergillus was identified as the most abundant isolates from the mites. Additionally, eight new isolates of Metarhizium belonging to the specie M. brunneum were identified. At all sites from which mites were collected in both seasons, the abundance of fungi on D. gallinae was greater during the winter season than during the summer season. Through indirect inoculations of adult D. gallinae, we examined the virulence of the native Metarhizium species, the commercial strain Ma-43 and a previously described acaropathogenic strain (Ma-7). All of the Metarhizium strains caused 56–95% mortality of adult mites by seven days after inoculation at a concentration of 5 × 10⁵ conidia per cm². The efficacies of Ma-43, Ma-7 and the most promising native strain were tested under optimal abiotic conditions (28°C; 85–100% RH) and abiotic conditions similar to those typically found in a poultry house (30 °C; 60% RH). Under optimal conditions, the efficacy of all three stains ranged between 85 and 92%. In contrast, under poultry-house conditions, the efficacy of control ranged between 30 and 40%. The incidence of mycoses on mite cadavers was significantly decreased under poultry-house conditions. These results demonstrate the potential of native and commercial Metarhizium strains for use as biopesticides. Future research should address suitable delivery methods and formulations for the effective control of D. gallinae under poultry-house conditions.