The effect of Beauveria bassiana (Hypocreales: Cordycipitaceae) on the redlegged earth mite, Halotydeus destructor (Trombidiformes: Penthaleidae), evaluated through laboratory and microcosm trials

The redlegged earth mite (RLEM, Halotydeus destructor (Tucker)), a major agricultural pest in Australia, is primarily managed by synthetic pesticides. However, the emergence of pesticide resistance in many field populations has prompted growing interest in alternative biopesticides. In the laboratory, Beauveria bassiana (Balsamo-Crivelli) Vuillemin significantly affected both RLEM adults and nymphs when applied in vial or agar-based bioassays, but not in a leaf dip assay. A field rate of a commercial formulation of Beauveria registered for control of 2-spotted spider mites significantly reduced RLEM survival and reproduction. Lower concentrations decreased mite survival but paradoxically increased reproductive output. In a microcosm ‘semi-field’ trial, all tested concentrations of Beauveria reduced the survival of RLEM adults but did not necessarily decrease net reproductive output. In conclusion, B. bassiana has efficacy against RLEM, however a hormetic effect at low concentrations may enhance offspring production. Further research is necessary to explore optimal concentrations, thermotolerance, product formulations, mite life stages, and field-based efficacy.