Susceptibility of the Two-Spotted Spider Mite, Tetranychus urticae Koch, to the Fungal Pathogen Hirsutella thompsonii Fisher

Abstract

Laboratory bioassays determined the susceptibility of the two-spotted spider mite, T. urticae Koch, to H. thompsonii thompsonii Fisher. Direct placement of conidia onto mites which were placed on bean leaf discs floating on distilled water in covered petri dishes yielded a mean mortality of 96.5%. Mortality of mites placed on leaf discs cut from bean plants previously sprayed with a commercial formulation of the bioacaricide and placed in the covered dishes ranged from .apprx. 24-99%. No significant response to dose of Mycar occurred at the rates tested (1.2-9.6 g/l). Under greenhouse conditions (22.degree.-30.degree. C; 50-90% RH [relative humidity]), the formulated material failed to either sporulate on sprayed foliage or cause mite mortality. Raising humidity levels with intermittent misting of foliage increased sporulation of the fungal inoculum on plant surfaces, but no infections occured in mites on those plants.