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Pathogenicity of four strains of entomopathogenic fungi against the bovine tick Boophilus microplus

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  • 1 Department of Agronomy, Federal Center of Technological Education of Paraná, Pato Branco, Brazil Onofre, Miniuk and the Department of Biological Sciences, University of Caxias do Sul Biotechnology Institute, Caxias do Sul, Brazil Barros, Azevedo.
  • | 2 Department of Agronomy, Federal Center of Technological Education of Paraná, Pato Branco, Brazil Onofre, Miniuk and the Department of Biological Sciences, University of Caxias do Sul Biotechnology Institute, Caxias do Sul, Brazil Barros, Azevedo.
  • | 3 Department of Agronomy, Federal Center of Technological Education of Paraná, Pato Branco, Brazil Onofre, Miniuk and the Department of Biological Sciences, University of Caxias do Sul Biotechnology Institute, Caxias do Sul, Brazil Barros, Azevedo.
  • | 4 Department of Agronomy, Federal Center of Technological Education of Paraná, Pato Branco, Brazil Onofre, Miniuk and the Department of Biological Sciences, University of Caxias do Sul Biotechnology Institute, Caxias do Sul, Brazil Barros, Azevedo.

Abstract

Objective—To evaluate the pathogenicity of 4 strains of the entomopathogenic 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 conidial suspensions of the 4 fungal strains; a control group of 60 females was treated with sterilized water.

Procedure—For each fungal strain, sporulating cultures were used to produce conidial suspensions containing 104, 105, 106, 107, and 108 conidia/ml. A bioassay was performed by immersing B microplus females in conidial 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 same volume of sterilized distilled water. Ticks were maintained at 27 C and 80% relative humidity for 7 days, and the following variables were evaluated: weight before egging, egging weight, percentage eclosion, reproductive efficiency, and percentage control.

Results—A low index of eclosion was found in the treated groups, with a progressive decrease in percentage eclosion (control = 100%) with increased conidial concentration. The highest level of effectiveness of biocontrol was detected in groups treated with concentrations of 107 and 108 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 flavoviridestrain CG-291 being the most effective. The pathogenicity of these strains and the development of an application method for this fungus for control of ticks may result in improved animal productivity and a reduction in environmental pollution through the use of fewer chemical insecticides. (Am J Vet Res 2001;62:1478–1480)

Abstract

Objective—To evaluate the pathogenicity of 4 strains of the entomopathogenic 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 conidial suspensions of the 4 fungal strains; a control group of 60 females was treated with sterilized water.

Procedure—For each fungal strain, sporulating cultures were used to produce conidial suspensions containing 104, 105, 106, 107, and 108 conidia/ml. A bioassay was performed by immersing B microplus females in conidial 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 same volume of sterilized distilled water. Ticks were maintained at 27 C and 80% relative humidity for 7 days, and the following variables were evaluated: weight before egging, egging weight, percentage eclosion, reproductive efficiency, and percentage control.

Results—A low index of eclosion was found in the treated groups, with a progressive decrease in percentage eclosion (control = 100%) with increased conidial concentration. The highest level of effectiveness of biocontrol was detected in groups treated with concentrations of 107 and 108 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 flavoviridestrain CG-291 being the most effective. The pathogenicity of these strains and the development of an application method for this fungus for control of ticks may result in improved animal productivity and a reduction in environmental pollution through the use of fewer chemical insecticides. (Am J Vet Res 2001;62:1478–1480)