The recommended treatment regimen against Varroa increases colony survival
Adherence to recommended treatment regimens against Varroa destructor improves the winter survival of honey bee colonies. Key findings:
- Compliance of beekeepers with recommended control measures against the mite Varroa destructor was assessed.
- Mite infestation levels and honey bee colony mortality were measured to evaluate the impact of compliance.
- Non-compliance resulted in higher mite infestation rates and increased colony mortality.
- A colony had up to a 25-fold higher risk of death when it was not treated as recommended.
- Communicating the impact of deviations from recommendations improves compliance.
Abstract
The ectoparasitic mite Varroa destructor negatively affects the health and survival of honey bee colonies, thereby requiring beekeepers to treat their colonies every year. A widely used mite control regimen is based on two organic compounds: formic acid and oxalic acid. To ensure optimal efficacy, several applications of these acids at predefined times are recommended. These recommendations are mainly based on experiments conducted under controlled conditions. There are no studies assessing effectiveness under natural field conditions.
We recruited 30 beekeepers for a longitudinal study in three Swiss cantons and monitored the management and health of their colonies over a two-year period. We assessed compliance with mite control recommendations and measured infestation levels with V. destructor, indicators of colony productivity (brood size and honey yield), and colony mortality in 300 colonies.
We observed a tenfold higher risk of colony death when beekeepers deviated slightly from the recommended treatment regimen compared with compliant beekeepers (odds ratio: 11.9; 95% CI: 2.6–55.2; p = 0.002). The risk of colony mortality was increased 25-fold in apiaries with substantial deviations from the recommendations (odds ratio: 50.4; 95% CI: 9.7–262.5; p < 0.0001). Deviations resulted in increased levels of V. destructor infestation prior to overwintering, which was likely responsible for the observed colony mortality. After communicating the apparent link between low compliance and low colony survival to beekeepers at the end of the first year, we observed improved compliance and higher colony survival during the second year.
Our results highlight the positive impact of adherence to the recommended therapeutic regimen against V. destructor on honey bee colony health and the need to better communicate the consequences of deviating from recommendations in order to improve compliance. Compliance also occasionally declined, suggesting the presence of implementation constraints that could be identified and potentially addressed in more detail using social sciences to further promote honey bee health.
Keywords
Apis mellifera ; Parasite control ; Varroa destructor ; Compliance ; Colony mortality ; Beekeeping management