Commercial formulation of Metarhizium anisopliae for the control of Rhipicephalus microplus in a pen study

•Metarhizium anisopliae oil formulation against Rhipicephalus microplus in pen study.•The average efficacy of Metarril® oil-based formulation was roughly 47%.•Oil formulation reduced the hatching percentage and egg production index of ticks.•Metarril® oil-based formulation was efficient against R. microplus in pen studies.

The present study evaluated, for the first time, the effect of the commercial formulation Metarril® SP Organic of Metarhizium anisopliae plus 10% mineral oil to control Rhipicephalus microplus in a pen study. Three groups were formed with six animals each: the first group was exposed to Metarril® plus 10% mineral oil and 1% Tween 80; the second group was exposed to sterile distilled water, mineral oil and Tween 80 (oil control group); and the third group received no treatment (control group). The fungal formulation contained 1 × 108 conidia ml−1. Each animal was sprayed with 3 L of formulation. Fallen ticks were counted daily and a sample of 20 engorged females per day was incubated for assessment of biological parameters. Throughout the study period, Metarril® oil-based formulation showed an efficacy ranging from 19.20% to 67.39% in comparison with the control group; and from 8.18% to 61.38% in comparison with the oil control group. The average efficacy of Metarril® oil-based formulation was 47.74% and 40.89% in comparison with control and oil control groups, respectively. Changes in the biological parameters of engorged R. microplus females were observed in the first three days after treatment, with a significant reduction in hatching percentage and egg production index. We concluded that Metarril® SP Organic plus 10% mineral oil was efficient against R. microplus in pen studies. However, further in vivo studies are required to increase the efficacy and to establish a protocol for the use of this product in the field against the cattle tick.