Examining Effects of Fungal Miticides on Varroa Mite Populations and Honey Bee Health

Commodities

• Animals: bees
• Animal Products: honey

Practices

• Animal Production: animal protection and health, inoculants, parasite control, preventive practices
• Crop Production: application rate management, beekeeping, biological inoculants, pollination, pollinator health
• Education and Training: demonstration, extension
• Pest Management: biological control, biorational pesticides, botanical pesticides, disease vectors, genetic resistance, integrated pest management, prevention
• Sustainable Communities: food access and security

This project evaluates entomopathogenic fungi (EF) as a sustainable biological control for Varroa mites, a leading cause of honey bee colony losses. Miticides remain the primary management tool, but resistance is widespread and concerns persist regarding residue contamination and long-term colony health. EF offer a promising alternative; however, their effectiveness has been limited by the high temperatures inside beehives. To address this limitation, thermally tolerant fungal strains developed through laboratory selection will be tested in field colonies to determine their ability to reduce Varroa populations under real-world conditions. Colonies will be monitored for mite mortality using standard assessment methods, and fungal strains will be re-isolated from infected mite cadavers to further select for virulence and host specificity in subsequent trials. In addition to evaluating efficacy against Varroa mites, this project will examine potential effects of fungal exposure on honey bee health. Adult worker bees will be sampled before and after treatment, and RNA sequencing will be used to assess changes in gene expression associated with immune function and overall colony health. This approach will determine whether fungal treatments provide secondary benefits beyond mite suppression. This research aims to advance development of a residue-free, sustainable Varroa management tool. Results will contribute to sustainable apiculture and provide beekeepers with a practical strategy for managing honey bee parasites.

Research Objectives:
(1) Determine the efficacy of heat tolerant strains for managing Varroa mite populations in field conditions.

(2) Evaluate the effect of fungal treatments on worker bees by analyzing changes in gene expression after exposure to EF treatment.

(3) Perform strain selection by re-isolating fungi from Varroa mite cadavers collected from treated colonies.

Educational Objectives:
(1) By Dec 2026, increase beekeeper knowledge of EF Varroa management strategies, measured by a pre/post 5-question quiz in a live presentation with ≥50 attendees.

(2) By Jan 2027, deliver one conference presentation (AHPA 2026) and one local/regional beekeeper meeting talk, documented by agenda listing and attendance counts.

(3) By Jan 2027, publish one 1-2 page WSU Extension factsheet summarizing results and practical uses.