Control of tick populations by spraying Metarhizium anisopliae conidia on cattle under field conditions

Conidia of the entomopathogenic fungus, Metarhizium anisopliae, in oil/water formulation (1 × 10(8) conidia/ml) were sprayed at 3 weekly intervals on Rhipicephalus evertsi evertsi and Rhipicephalus (Boophilus) decoloratus ticks while feeding on Afrikana bulls grazing in paddocks for a period of 1 year. The fungus reduced the on-host tick populations by 83% 3 month after commencement of the experiment. The formulation by itself had only minimal effect on the tick population. Tick populations and fungal efficacy were highest at the peaks of rainfall and relative humidity or soon thereafter. Fed and unfed adult R. e. evertsi and R. (B.) decoloratus collected at the end of the experiment from the fungus-sprayed and from the control cattle and incubated in the laboratory exhibited a mortality of 93% in oil formulated conidia and 14% in oil control. The corresponding mortality in R. (B.) decoloratus was 100% in fungus and 11% in oil control. Ticks on the fungus-sprayed groups had significantly higher mortality (P < 0.05) than on the control groups. Furthermore, no significant difference (P < 0.05) was observed in fungus-induced mortality between the two tick species. Mortalities induced by Triton X-100 (0.05%), sunflower oil (20%) and water alone were low, suggesting that they were non-toxic to ticks at the concentrations used and no significant difference was observed among them. No physical or behavioral abnormalities were observed in the fungus-sprayed cattle at any time during the course of the experiment. All groups of cattle gained weights during the experimental period.