The effects of the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) were evaluated against the common louse parasite of cattle, Bovicola bovis (Piaget) (Trichodectidae: Ischnocera). Two different concentrations and formulations of conidial
suspensions were applied to contained populations of adult female lice. In vitro, lice immersed in
suspensions of M. anisopliae formulated in 0.03%
Tween 80 developed
infections; at the highest concentration (1x10(8)conidia ml-1) a mean of 71% (+/-11.52%, 95% C.I.) of lice became infected. Lice exposed to the
Tween 80 only in vitro, showed high levels of survival and zero
infection. In vivo, fungal conidia were applied to louse populations contained in 7 cm diameter circular arenas glued to the backs of Holstein cattle, maintained in controlled climate conditions. Conidia were formulated in either
Tween 80 or
silicone oil. The treatment with M. anisopliae resulted in high levels of
infection and there was no overall difference between the two formulations in the number of
infections observed. At the highest concentration (1x10(8)conidia ml-1) a mean of 73% (+/-15.57%, 95% C.I.) lice became infected. It is concluded that the strategic seasonal use of a fungal pathogen on cattle, applied in early winter, may be of value in suppressing the winter increase in abundance, preventing the population increasing to clinically significant levels.