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

摘要

This study was conducted to determine the action of isolates JAB 07, CB 7 and AM 9 of the fungus Beauveria bassiana on the eggs, larvae and engorged nymphs of Rhipicephalus sanguineus. 109 conidia/ml was standardized for each isolate, and suspensions containing 108 and 107 conidia/ml were obtained by serial dilution. A bioassay was prepared for each life cycle phase of the tick. Each assay comprised of 10 treatment groups, consisting of one fungal isolate, one conidial concentration and one control group containing only the suspension vehicle. For the egg infection, 0.1 g (about 270 eggs) was placed in one ml suspension at different concentrations. Each engorged larvae (n=250) and nymph groups (n=50) received 2 ml of one conidial suspension. The eggs, larvae and nymphs were placed in an incubator at 27+or-1 degrees C and humidity above 80%. The fungal isolates applied at different spore concentrations decreased the percentage of hatching larvae derived from infected eggs (0.7 to 12.1% of hatching) as well as the ecdysis of larvae (7.7 to 33.7% of ecdysis) and nymphs (0 to 16.7% of ecdysis). No difference in the infectivity to eggs was observed between the isolates, but the application of 109 conidia/ml of JAB 07 and AM 9 significantly decreased the hatching of larvae compared to the 107 conidia/ml concentration. The isolate CB 7 was more efficient in reducing the number of larval ecdysis. The isolates and concentrations tested did not differ in their ability to reduce the ecdysis percentage of nymphs, but an intense pathogenic activity of the fungus was observed..