Metarhizium anisopliae sensu lato (s.l.) oil‐in‐water emulsions drastically reduced Rhipicephalus microplus larvae outbreak population on artificially infested grass

Rhipicephalus microplus Canestrini, 1887 (Arachnida: Ixodidae) is a mandatory bloodsucking ectoparasite, and it is considered one of the main sanitary problems in livestock. In the development of new technologies for controlling ticks, Metarhizium anisopliae complex (M. anisopliae s. l.) Sorokın, 1883 (Ascomycota: Clavicipitaceae) have been shown to be an effective and safe alternative. However, when applied in the field, abiotic factors may directly influence their microbial activity, and different oily adjuvants enhance fungal efficacy, stability and viability under environmental conditions. Here, the efficacy of two Metarhizium anisopliae s.l. isolates (CG 148 and CG 347) were compared in mineral oil (MO) or vegetable oil (VO) emulsions to control cattle ticks under semi‐natural conditions, as well as their persistence in the soil over time. Engorged female ticks were placed on the soil of grass pots previously treated or not with conidial oil‐in‐water emulsions. Both M. anisopliae s.l. oil‐in‐water emulsions tested were able to control R. microplus, achieving up to 100% daily efficacy, and remained viable in the soil for up to 60 days after treatment. These results show the prospective applicability of Metarhizium spp. to control the cattle tick and a real possibility for its control in the environment. Metarhizium anisopliae s.l. isolates formulated in soybean or mineral oil‐in‐water emulsions persisted in the soil for up to 60 days. Soil drenched with Metarhizium anisopliae s.l. oil‐in‐water emulsions is a promising strategy for the biological control of ticks. Rhipicephalus microplus females were infected and killed when exposed to soil treated with Metarhizium anisopliae s.l., reducing future generations of this tick.