Efficiency of Lecanicillium lecanii to control the tick Rhipicephalus microplus

Abstract

Rhipicephalus microplus, known as the cattle tick, causes serious economic losses in the Brazilian cattle industry each year. Traditional parasite control is primarily based on the use of chemical acaricides, which unfortunately have many negative side effects. Biological control is seen as a promising alternative to chemical acaricide use. This study evaluates the entomopathogenic fungus Lecanicillium lecanii for effectiveness in controlling engorged females, eggs, and larvae of R. microplus. Conidial formulations of L. lecanii, isolate CG 420, were prepared in both oil (15% mineral oil) and aqueous suspensions. Ticks were immersed in a 1 ml oil-based conidial suspension at 1 × 10 8 conidia ml −1 or one of several aqueous conidial suspensions at 1 × 10 5, 10 6, 10 7 or 10 8 conidia ml −1. The control groups were immersed in water or oil solutions with no conidia. Treatments with aqueous conidial suspensions were conducted with 10 ticks per group (1 × 10 5, 10 6, 10 7, 10 8 conidia ml −1 or control) whereas the oil treatments used 30 ticks per group (1 × 10 8 conidia ml −1 or control). Bioassays were repeated twice on different days with different batches of conidia. After treatment, the biological parameters of engorged females were evaluated, while eggs and larvae were evaluated taking into consideration hatchability and mortality, respectively. The results indicate that L. lecanii has the potential to control engorged females, eggs and larvae of R. microplus. Better results were observed when conidial oil-based suspension was used. In general, engorged females treated with 1 × 10 8 conidia ml −1 oil suspensions died before laying eggs, resulting in 97.6% of tick control. As far as we know, this is the first report of the effects of L. lecanii on R. microplus tick.