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

Abstract

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 entomopatógenos, Beauveria bassiana GHA y Metarhizium anisopliae UAMH 9198, para controlar Varroa destructor en colonias de abejas melíferas se determinó a principios de otoño en una zona con clima frío. Los tratamientos fúngicos se aplicaron en colmenas como conidios secos mezclados con harina de maíz, solos, o en combinación con un tratamiento de timol. Los tratamientos se aplicaron usando dos métodos de administración, bandeja dispensadora y espolvoreador. Los tratamientos combinados de hongos y timol mostraron la eficacia acaricida más alta (> 82%), pero estos tratamientos no fueron significativamente diferentes a los tratamientos con timol sólo para el control de los ácaros. De los tratamientos fúngicos aplicados solos, M. anisopliae UAMH 9198 administrado con bandeja dispensadora causó una mortalidad de ácaros significativamente mayor que los tratamientos testigos (62%, p < 0.0001). Los tratamientos de B. bassiana GHA aplicados solos también tuvieron una tasa significativamente más alta de eficacia acaricida en comparación con los testigos, pero las tasas de eficacia fueron relativamente bajas (41–53%). Hubo interacciones significativas entre el tratamiento con hongos y el método de administración. M. anisopliae UAMH 9198 aplicado con bandeja fue significativamente más efectivo en el control de los ácaros que cuando se aplicó con un espolvoreador, mientras que lo contrario ocurrió para B. bassiana GHA.

Keywords:

• entomopathogenic fungi
• biocontrol
• thymol
• Varroa destructor
• Apis mellifera
• Beauveria bassiana
• Metarhizium anisopliae

Acknowledgements

We are grateful to Paul Kelly for supplying the bees and managing the hives used in the experiments, as well as for designing and building the dispenser trays. We are also thankful to Nancy Bradbury, Miriam Martin, David Stotesbury and Mildred Delgado for their assistance with the experiments. We acknowledge the University of Alberta Microfungi Collection for supplying the Metarhizium anisopliae fungal isolate.