Background and aims: Fungi from the genus Metarhizium are used increasingly in commercial formulations against insects. But a few field experiments have been performed to kill ticks with these fungi. The development of tick resistance to acaricides and our awareness that chemicals are harmful to the environment, this study was conducted with the aim to evaluate efficacy of applying 4 different formulations of Metarhizium anisopliae fungus to combat Hyalomma ticks.

 Methods: In this experimental study, 4 different formulations were used which included: 1) Distilled water with 2% Tween and Metarhizium anisopliae, 2) Distilled water with 10% cotton seed oil, 0.01% sucrose, 0.2% tween and Metarhizium anisopliae, 3) Distilled water with 10% liquid paraffin, 0.01% sucrose, 0.2% tween and Metarhizium anisopliae and 4) distilled water as the control group. The four prepared formulations were equally sprayed on 128 mature ticks, in 4 groups. Number of dead ticks due to spray of formulations were counted in the following days. Treatment effect based on mortality of ticks, was assessed using time-survival analysis.

 Results: Though of the suspensions made with water, liquid paraffin, cotton seed oil and the fungus, cotton seed oil suspension was the best treatment effect, but there were not significant differences between these three groups. There were significant differences between these groups and control group (P<0.05).

 Conclusion: Oil suspension containing Metarhizium anisopliae fungus can be used instead of toxic chemicals compounds to eliminate Hyalomma ticks from farm animal bodies, with no harm to the environment, animals and humans. Therefore, further research is recommended in this regard.