OAHN Bee Network Project: Tracking natural varroa mite population growth in honey bee colonies

Project Lead: Dr. Colette Mesher

Collaborators:  Paul Kozak

To download the full report for this project, please click here: https://www.oahn.ca/wp-content/uploads/2024/01/Final-Report-OAHN-Varroa-Population-Growth.pdf


The goal of this study was to examine Varroa population growth across a season and into the next spring using a number of different monitoring methods, in order to answer questions around the timing and efficacy of mite monitoring. In addition, this study also examined the effect mite levels have on colony growth and overwinter survival. Both the alcohol wash and sticky board were able to capture Varroa population growth over the season, with lower levels of mites seen in the spring and higher infestations seen in the late summer and fall. In contrast, uncapping brood was not found to be a reliable technique for determining Varroa infestation. Mites were found under the cappings for the most highly-infested colonies, but not found for the majority of the test colonies, including those where the alcohol wash and sticky board detected mites. Mite levels were consistently lower in the isolated test yard in Port Loring, Ontario at all time points compared to the three test yards in Guelph, Ontario. Regression analyses found that the probability of a colony dying overwinter increased with increasing mite levels in September using all three monitoring methods. However, none of the three regression analyses were significant at p = 0.05. A surprising finding from the study was that colonies with larger adult bee populations in September were significantly more likely to die over the winter. While part of these findings can be explained by larger colonies having higher mite levels, an important factor was likely large colony populations in September being associated with colonies that swarmed late in the year, leading to queen issues and colony overwinter mortality. Large populations in September were not associated with large cluster sizes in November (and possible starvation over winter). Colonies with small cluster sizes in November were more likely to die over the winter.