Resumo

Metarhizium anisopliae is an entomopathogenic fungus that has proven action in biological control of various insects in agriculture and livestock. The cattle tick Boophilus microplus is a serious concern to the Brazilian cattle industry. It causes decreased meat and milk production, low alimentary conversion, damage to leather and transmission of pathogens. The use of entomopathogenic fungi as biological control agents for ticks has shown promising results. This study tests the in vitro effects of one M. anisopliae isolated on the tick B. microplus, in order to select for use in biological control of insects. We used an isolate of M. anisopliae collected soil of an agroforestry system in the forest zone of Pernambuco. For the microscopic analysis, we used the culture medium Sabouraud-dextrose-agar. The pathogenicity test was performed in 30 female B. microplus. The bioassay was composed of one treatment group (concentration: 108 conidia/mL and the control) with three repetitions. The ticks were treated by immersion for three minutes. The pathogenic fungal activity was demonstrated by the difference statistically significant, observed between the control and treatment. Averages were compared by Tukey test at a significance level of 5%. Microscopic observations showed the formation of vegetative and reproductive structures from the spore germination. Between 48 and 72 hours were observed mycelial differentiation, formed by hyphae hyaline, septate, uninucleate, appressoria, anastomosis, simple conidiophores, elongated and uninucleate conidia. Germination of conidia on the surface of the cuticle of the tick, occurred from 48 hours after infection. The most intense colonization was observed only after 96 hours. From this period, mummification and disruption of the cuticle of the tick was observed. M. anisopliae caused a mortality rate of 96%, 83% and 100% in three repetitions, respectively (mean 93%) compared with the control group (mean 3.0%). Based on statistical analysis, the mean of three repetitions did not differ significantly by Tukey test, but there was a significant difference in mortality in the control group. The cytological analysis showed characteristic structures of M. anisopliae. In vitro test, M. anisopliae showed effective control of B. microplus, suggesting high potential for their use as a microbial control agent of the B. microplus tick.