Performance of Metarhizium anisopliae and Its Combination with Deltamethrin against a Pyrethroid‐Resistant Strain of Boophilus microplus in a Stall Test

Abstract

The use of the entomopathogenic fungus, Metarhizium anisopliae, to control ticks is a promising alternative to chemical acaricides, but both chemical and biological products could also work together in an integrated management. The current study evaluated the performance of M. anisopliae and its combination with deltamethrin to control a Boophilus microplus strain resistant to pyrethroid. Calves were held in individual pens and artificially infested with B. microplus. They were treated with an aqueous conidial suspension of M. anisopliae, a deltamethrin solution, or both fungus and deltamethrin combined. After treatment, engorged females that naturally dropped off from calves were counted daily and evaluated in the laboratory. The mean mortality rate was 32.57% in the groups treated with M. anisopliae, 38.58% in those groups treated with deltamethrin, and 30.92% in those treated with fungus and chemical combined. Additionally, ticks that dropped off from calves after 2 days had a lower nutrient index (NI) and egg production index (EPI) than those that dropped off at a later day after treatment. This indicates that M. anisopliae may reduce B. microplus population only for a few days after treatment when a simple aqueous conidial suspension was used.