Pathogenicity of four strains of entomopathogenic fungi against the bovinetick Boophilus microplus

Objective-To evaluate the pathogenicity of 4 strains of the entomopathogeni c fungi Metarhizium flavoviride var flavoviride and Metarhizium anisopliae var anisopliae in vitro against the bovine tick Boophilus microplus. Sample Population-300 B microplus females were used for each series of 5 co nidial suspensions of the 4 fungal strains; a control group of 60 females w as treated with sterilized water. Procedure-For each fungal strain, sporulating cultures were used to produce conidial suspensions containing 10(4), 10(5), 10(6), 10(7), and 10(8) coni dia/ml. A bioassay was per-formed by immersing B microplus females in conid ial suspensions; the procedure was repeated with a new group of 60 females for each dilution (a total of 300). A control group was immersed in the sam e volume of sterilized distilled water. Ticks were maintained at 27 C and 8 0% relative humidity for 7 days, and the following variables were evaluated : weight before egging, egging weight, percentage eclosion, reproductive ef ficiency, and percentage control. Results-A low index of eclosion was found in the treated groups, with a pro gressive decrease in percentage eclosion (control=100%) with increased coni dial concentration. The highest level of effectiveness of biocontrol was de tected in groups treated with concentrations of 10(7) and 10(8) conidia/ml. Conclusions and Clinical Relevance-Strains of the entomopathogenic fungi M anisopliae var anisopliae and M flavoviride var flavoviride were effective as biological control agents against B microplus, with M flavoviride strain CG-291 being the most effective. The pathogenicity of these strains and th e development of an application method for this fungus for control of ticks may result in improved animal productivity and a reduction in environmenta l pollution through the use of fewer chemical insecticides.