Evaluation of the entomopathogenic fungi Beauveria bassiana GHA and Metarhizium anisopliae UAMH 9198 alone or in combination with thymol for the control of Varroa destructor in honey bee (Apis mellifera) colonies

The efficacy of two entomopathogenic fungi, Beauveria bassiana GHA and Metarhizium anisopliae UAMH 9198 for controlling Varroa destructor in honey bee colonies was determined during early fall in a northern climate. Fungal treatments were applied in hives as dry conidia mixed with corn flour either alone, or in combination with a thymol treatment. The treatments were applied using two delivery methods, dispenser tray and duster. The combined treatments of fungi and thymol showed the highest miticidal efficacy (>82%) but these treatments were not significantly different to thymol only treatments for mite control. Of the fungal treatments applied alone, M. anisopliae UAMH 9198 delivered by dispenser tray caused significantly higher mite mortality than the control treatments (62%, p<0.0001). Treatments of B. bassiana GHA applied alone also had a significantly higher rate of miticidal efficacy relative to controls, but the rates of efficacy were relatively low (41-53%). There were significant interactions between fungal treatment and delivery method. M. anisopliae UAMH 9198 delivered by tray was significantly more effective at controlling mites than when applied with a duster, whereas the opposite occurred for B. bassiana GHA. La eficacia de dos hongos entomopatogenos, Beauveria bassiana GHA y Metarhizium anisopliae UAMH 9198, para controlar Varroa destructor en colonias de abejas meliferas se determino a principios de otono en una zona con clima frio. Los tratamientos fungicos se aplicaron en colmenas como conidios secos mezclados con harina de maiz, solos, o en combinacion con un tratamiento de timol. Los tratamientos se aplicaron usando dos metodos de administracion, bandeja dispensadora y espolvoreador. Los tratamientos combinados de hongos y timol mostraron la eficacia acaricida mas alta (> 82%), pero estos tratamientos no fueron significativamente diferentes a los tratamientos con timol solo para el control de los acaros. De los tratamientos fungicos aplicados solos, M. anisopliae UAMH 9198 administrado con bandeja dispensadora causo una mortalidad de acaros significativamente mayor que los tratamientos testigos (62%, p < 0.0001). Los tratamientos de B. bassiana GHA aplicados solos tambien tuvieron una tasa significativamente mas alta de eficacia acaricida en comparacion con los testigos, pero las tasas de eficacia fueron relativamente bajas (41-53%). Hubo interacciones significativas entre el tratamiento con hongos y el metodo de administracion. M. anisopliae UAMH 9198 aplicado con bandeja fue significativamente mas efectivo en el control de los acaros que cuando se aplico con un espolvoreador, mientras que lo contrario ocurrio para B. bassiana GHA.