How Do We Save the Bees from Varroa?
Varroa destructor mites vector a myriad of disease and viruses to honey bees, like Deformed Wing Virus (DWV) causing wing and abdominal deformities and Lake Sinai virus (LSV) which is commonly associated with colony collapse disorder. EPA registered mite treatment options are losing efficacy. It is time for a novel approach to the million-dollar question for beekeepers worldwide – how do we save the bees from Varroa destructor mites? Scientists from Fungi Perfecti LLC, Washington State University and USDA explore antiviral compounds in fungal extracts to reduce DWV and LSV viral load in honey bees afflicted by Varroa.
Extracts of Polypore Mushroom Mycelia Reduce Viruses in Honey Bees
The consequences are grave if we are unable to find safe, effective, long term solutions to manage Varroa destructor mites and the diseases they vector to honey bees. World renowned mycologist and owner of Fungi Perfecti LLC, Paul Stamets, has teamed up with Washington State University to test the efficacy of viral reduction in honey bees using fungal extracts (see video). Their recent publication in Nature has received worldwide attention as the first potential antiviral solution for honey bees.
Stamets et al. isolated extracts of Hoof Fungus (Fomes fomentarius), Artist’s Conk (Ganoderma applanatum), Reishi (Ganoderma resinaceum) and Turkey Tail (Trametes versicolor) (Figure 1). Researchers collected and placed worker bees in cages where they were kept for 7 days, receiving mushroom extracts mixed into a 1:1 sugar/water syrup. At the end of 7 days, the bees were tested to determine viral load. Different groups of bees received different concentrations of mycelial extract (0.01%, 0.1%, or 1%). The highest concentration (1%) resulted in the highest efficacy in reducing viral load. A similar experiment was conducted in the field on nucleus colonies using 1% mycelial extracts of F. fomentarius and G. resinaceum. Nucleus colonies were sampled for viral load prior to and 12 days following treatment.
The researchers saw significant viral reduction in all mycelial extract treated colonies compared to the control in caged laboratory trials. Mycelial extract treated colonies saw an overall 23-fold reduction in DWV (sample size (n)=58, probability (p)=0.0001) and 21-fold reduction in LSV (n=10, p=0.004). F. fomentarius (1%) showed the most dramatic results with an 800-fold reduction in DWV (p=0.005). G. resinaceum showed a 500-fold reduction in LSV but showed the greatest variance (p=0.08).
Researchers used DNA analysis to validate the reduction in DWV and LSV in field nucleus colonies 12 days after mycelial extract treatment. F. fomentarius showed a 79.7-fold reduction in DSW (n=18, p=6.32 × 10−6) and 87.9-fold greater reduction in LSV (n=18, p=0.02) than in control colonies. G. resinaceum showed a 79.6 greater fold reduction in DWV than control colonies (n=20, p= 1.31 × 10−8). G. resinaceum showed the most promising result in the field for LSV reduction with a 45,000-fold greater reduction than control colonies (n=20, p=5.34 × 10−6).
In addition to mycelial extracts, birch fungal growth substrate (sawdust) containing endophytic and saprophytic fungal associates (Graphostroma platystoma, Chondrostereum purpureum, Trametes versicolor) may provide anti-viral benefits that will be explored in future studies to distinguish if birch wood phytochemicals like betulinic acid aid in viral reduction provided by the fungal associates.
Results from these trials are promising but not conclusive. Mycelial extracts may play an important role in future varroa treatment options, however, the mechanisms that reduce viral load are still unknown. Additional research into possible negative side effects, long term safety and health of honey bees should be assessed as many EPA registered varroacides can be harmful to beekeepers and/or the honey bees. Before marketing the mycelial extracts to beekeepers worldwide, Paul Stamets and WSU colleagues must follow up with treated colonies, validate results on a larger scale, and determine best management practices.
Stamets, P; Naeger, N; Evans, J; Han, J; Hopkins, B; Lopez, D; Moershel, H; Nally, R; Sumerlin, D; Taylor, A; Carris, Sheppard, W. L. 2018. Extracts of Polypore Mushroom Mycelia Reduce Viruses in Honey Bees. Nature 8, Article number: 13936.