Laboratory and field evaluation of Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) for the control of Rhipicephalus microplus (Acari: Ixodidae) in the Mexican tropics

The aim of the present study was to evaluate the effect of Metarhizium anisopliae to control Rhipicephalus microplus under laboratory and field conditions (larvae on vegetation) in the Mexican tropics. In the laboratory study, Ma34, Ma14 and a mixture of Ma34+Ma14 strains of M. anisopliae were evaluated for their control of the adult and larval stages of R. microplus, using the adult and larval immersion test respectively. The reproductive efficiency index of engorged females was determined in the treated and control groups. In the adults, the Ma34 and MA14 strains both produced an efficacy of 100% on engorged females at 1×10⁸, 1×10⁷ and 1×10⁶ conidia/ml; however, only Ma34 killed 100% at 1×10⁶ conidia/ml dose. The mixture of both strains (Ma34+Ma14) produced an efficacy of 100% on engorged females at 1×10⁸ conidia/ml. R. microplus engorged females treated with Ma34 and a mixture of strains Ma34 and Ma14 reduced egg oviposition by 55.5% and 39.1% respectively compared to treated controls (P <0.001). In the larval evaluation, Ma14 produced an efficacy of 45-62%; however, Ma34+Ma14 increased the efficacy reaching 90% (1×10⁸ conidia/ml concentrations, P <0.05). In the field study, twelve 9m² plots with vegetation were artificially infested with R. microplus larvae. Six plots were used as control and six as test areas. The treated plots received the Ma34+Ma14 (1×10⁸ conidia/ml) by manual scattering at 0, 14 and 28 days post-treatment (PT). The number of larvae in the treated and control group was determined at 0, 7, 14, 21, 28 and 35 days PT by the tick drag method. This field study was carried out in two different seasons (January-March, wet, April-May, dry). In the wet season trial the efficacy of M. anisopliae to control R. microplus was 67.7% and 100% in the dry season trial .In conclusion, the mixture of Ma34 and Ma14 strains of M. anisopliae showed a high efficacy to control both larval and adult stages of R. microplus under laboratory conditions, and in field conditions these strains were efficient to control larval stages on vegetation.