Effects of sheep fleece washings on the germination and growth of Beauveria bassiana

The development of biopesticides against ectoparasites must take into account the effect that an animal host’s secretions and host associated micro-organisms may have on the viability of the applied agent. In this study, the effects of secretions washed from the pelt of sheep on the viability and growth of the fungal pathogen Beauveria bassiana, were assessed. The fungal isolate had been obtained from the parasitic sheep scab mite Psoroptes ovis. It was added to 0.05% Tween 80 in which sheep fleece had been washed up to six times, to ascertain whether successive washings had any effect on the viability of conidia over 6 days. The effects of sterile and non-sterile washings on viability and growth were also investigated. Results indicated that substances in the sheep fleece may cause a significant reduction in the viability of conidia. Viability was linked to the number of times the sheep pelt had been washed in the Tween, with conidia incubated in the first wash from the sheep pelt showing a significantly greater decrease in viability compared to those incubated in the sixth wash. Viability was not linked to the sterility of the washes, although there was a significant difference between length of germ tube growth from viable conidia in sterile and non-sterile washings.