Pathogenicity of the entomopathogenic fungus Metarhizium anisopliae to the red-legged tick, Rhipicephalus evertsi evertsi

摘要

Rhipicephalus evertsi evertsi?is an economically-important tick of livestock in Africa mainly due to its ability to transmit?Babesia equi?to horses,?Anaplasma marginale?to cattle and to cause paralysis in lambs, adult sheep and calves. This study investigated the pathogenicity and hence the bio-control potential of?Metarhizium anisopliae?to eggs and all other off-host stages of?R. e. evertsi. The eggs and larvae were infected by placing them on filter paper wetted with conidial suspension. Tick instars were infected by dipping in?M. anisopliae?suspenssion (1×103–108conidia/ml) and incubated together with the eggs at 25°C and 100% relative humidity (RH). The mortality of eggs and all tick stages tested increased with increasing conidial concentration and were higher (P>0.05) in conidia formulated in oil than in those formulated in water. For instance, the LC50?in unfed larvae was 1×104?conidia /ml in oil formulation and 1×105?conidia /ml in water formulation. No difference was observed in mortality between fed and unfed tick stages.