What percentage of Varroa mites are in the phoretic state during the summer? Key Insights for Beekeepers

During the summer months, approximately 15-20% of Varroa mites are in the phoretic state, actively moving within the hive or attached to adult bees. The remaining 80-85% are found in capped brood cells, where they reproduce and feed on developing bee larvae. This distribution has significant implications for varroa mite treatment strategies, as most mites are protected within cells during this period.

Key Points Explained:

1. Phoretic vs. Reproductive Mites

   • Phoretic mites (15-20%): These are mobile mites clinging to adult bees or roaming the hive. They spread between colonies via drifting or robbing bees.
   • Reproductive mites (80-85%): These mites are hidden in capped brood cells, where they lay eggs and feed on pupae. Their protected location makes them harder to target with treatments.

2. Seasonal Dynamics

   • Summer’s high brood production creates abundant hiding spots for mites, reducing the phoretic population.
   • In contrast, winter (with little/no brood) forces nearly all mites into the phoretic state, making them more vulnerable to treatments like oxalic acid.

3. Treatment Implications

   • Summer challenges: Most mites are shielded in brood cells, requiring treatments that penetrate capped cells (e.g., formic acid or thymol-based products).
   • Timing matters: Integrated Pest Management (IPM) strategies should combine summer treatments with brood breaks or trapping frames to reduce protected mite populations.

4. Monitoring Tips

   • Alcohol wash/sugar roll: Best for estimating phoretic mite levels.
   • Brood sampling: Necessary to assess total infestation, as phoretic counts alone underestimate the problem.

Understanding this balance helps beekeepers choose the right varroa mite treatment timing and methods, ensuring healthier colonies year-round.

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