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Pathogenicity of Beauveria bassiana isolates towards eggs, larvae and engorged nymphs of Rhipicephalus sanguineus

Nancy Prette Antonio Carlos Monteiro Marcos Valério Garcia Vando Edesio Soares About the authors

The aim of the present study was to determine the action of isolates JAB 07, CB 7 and AM 9 of the fungus Beauveria bassiana on eggs, larvae and engorged nymphs of Rhipicephalus sanguineus tick. A concentration of 109 conidia mL-1 was standardized for each isolate and suspensions containing 10(8) and 10(7) conidia mL-1 were obtained by serial dilution. A bioassay was prepared for each phase of the life cycle of the tick. Each assay comprised 10 treatment groups, consisting of one fungal isolate and one conidial concentration, and one control group containing only the vehicle of suspensions. For the eggs infection 0.1g (about 270 eggs) were placed at 1ml of suspension at different concentrations, each engorged larvae group (n=250) and engorged nymphs (n=50) received 2ml of one conidial suspension. Thereafter, eggs, larvae and nymphs were placed in on incubator at 27 ± 1°C and at a humidity above 80%. The fungal isolates applied at different spore concentrations caused a reduction in percent hatching of larvae derived from infected eggs (0.7 to 12.1% of hatching) and in percent ecdysis of larvae (4.7 to 33.7% of ecdysis) and nymphs (0 to 16.7% of ecdysis). No difference in the infection of eggs was observed between isolates (P>0.05), but the application of 109 conidia/ml of JAB 07 and AM 9 significantly reduced the hatching of larvae compared to the concentrations of 10(7) conidia mL-1. The isolate CB 7 was more efficient in reducing the number of larval ecdysis. The isolates and concentrations tested didn’t differ (P>0.05) in their ability to reduce percent ecdysis of nymphs, but an intense pathogenic activity of the fungus was observed.

biological control; entomopathogenic fungus; microbial control; tick

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