Pathogenicity of Metarhizium anisopliae (Deuteromycetes) and permethrin to Ixodes scapularis (Acari: Ixodidae) nymphs
Effectiveness of the entomopathogenic fungus Metarhizium anisopliae , for controlling nymphal Ixodes scapularis , was tested in laboratory and field trials. In the laboratory, M. anisopliae (Metschnikoff) Sorokin strain ESC1 was moderately pathogenic, with an LC 50 of 10 7 spores/ml and induced 70% mortality at 10 9 spores/ml. In a field study, however, 10 9 spores/ml M. anisopliae did not effectively control questing I. scapularis nymphs, and significant differences were not detected in pre- and post-treatment densities. For nymphs collected and returned to the laboratory for observation, mortality was low in treatment groups, ranging from 20 to 36%. To assess whether a chemical acaricide would synergistically enhance pathogenicity of the fungus, we challenged unfed nymphal I. scapularis with combinations of M. anisopliae and permethrin, a relatively safe pyrethroid acaricide, in two separate bioassays. Significant interactions between M. anisopliae and permethrin were not observed, supporting neither synergism nor antagonism.