Effect of entomopathogenic native fungi from paddock soils against Rhipicephalus microplus larvae with different toxicological behaviors to acaricides.

The objectives of this study are to: (1) evaluate the in vitro acaricidal effect of 54 Metarhizium anisopliae strains, six Beauveria bassiana strains and one Purpureocilium lilacinum strain, against the larvae of two populations of Rhipicephalus microplus (multi-resistant and susceptible to chemical acaricides); and (2) determine the lethal concentrations required to eliminate the 50% (LC50) and 99% (LC99) of larvae through the use of entomopathogenic fungi (EF) with high acaricidal effects. The mortality percentage was evaluated by larval immersion tests at a dose of 1 × 10 conidia/mL for each fungal strain. For calculating LC50 and LC99, four doses (1 × 10, 1 × 10, 1 × 10 and 1 × 10) were used. Nine strains of M. anisopliae and the P. lilacinum strain showed a high mortality percentage in the R. microplus larvae of both populations. The best strains that showed the lowest values of LC50 and LC99 for tick elimination were MaV50 and PlV01. In conclusion, several strains of entomopathogenic fungi showed a high acaricidal effect against the R. microplus larvae of both populations, suggesting that these fungi might be a promissory adjuvant in the control of R. microplus, including those who are resistant. Finally, the discovery of a P. lilacinum strain with a high acaricidal effect is also reported.