The objective of this study was to evaluate the toxicity of the pyrethroid deltamethrin on the entomopathogenic fungus Metarhizium anisopliae var. anisopliae, considering the conidia germination speed as parameter. Suspended conidia in a concentration of 5.42 x107 conidia/ml were treated with deltamethrin at concentrations of 50 μg/ml, 250 μg/ml, 500 μg/ml, 750 μg/ml (diluted treatments), 31.25 ρg/ml, 31.25 ηg/ml and 31.25 μg/ml (ultra diluted treatments) and incubated for 24 h. Samples were collected among 0 and 24 h of incubation, then germinated conidia were counted, assessing the percentage of germination and germination speed. The results showed that 50 μg/ml of deltamethrin reduced and delayed conidia germination and it was 100% inhibited by the concentrations of 250 μg/ml to 750 μg/ml. Ultra diluted treatments with deltamethrin were not inhibitory and treatments with 31.25 ρg/ml and 31.25 ηg/ml of deltamethrin showed a significant increase of germinated conidia, indicating a possibly hormesis, that is, the biological effects of low level exposures of these concentrations of deltamethrin on conidia germination of M. anisopliae.
