The use of entomopathogenic fungi for the control of parasitic mites, Psoroptes spp

Abstract

In vitro trials were carried out to evaluate the potential of fungal pathogens as biological control agents of parasitic mites, Psoroptes ovis (Hering) (Acari: Psoroptidae) from rabbit hosts (synonym: Psoroptes cuniculi). The fungus Hirsutella thompsonii Fisher showed no pathogenicity. Metarhizium anisopoliae (Metschinkoff), however, showed a high level of pathogenicity; 3 days after exposure to fungal conidia all mites were dead and 6 days after exposure 60% of the dead adult females, 10% of the dead adult males and 30% of the dead female nymphs had fungal hyphae protruding from their cuticular surface. There was a significant effect of conidial concentration on the number of mite cadavers that displayed fungal infection. Exposure to between 1x10(4) and 1x10(6) conidiaml(-1) resulted in 2-25% of the mites being infected. Mean infection levels were highest, 71%, when the mites were exposed to 1x10(7) conidiaml(-1). Similarly, there was a significant effect of conidial concentration on the time taken for the mites to reach 50% levels of mortality (LT(50)) The mean LT(50) value was approximately 2.7 days, when the mites were exposed to a solution of 1x10(7) and 1x10(8) conidiaml(-1) which was significantly shorter than controls exposed to 0.03% Tween-80 solution only. There was no significant effect of passaging the fungus, either once or twice, through the host on the subsequent infectivity of M. anisopliae. The potential for use of entornopathogenic fungi for the control of parasitic mites, particularly in relation to sheep, is discussed.