Drone brood frame
Some acaricides used in alternative control strategies against Varroa, such as formic acid or essential oils, do not always provide sufficient efficacy. As complementary measures, we recommend the removal of drone brood or the establishment of young colonies in spring. These interventions aim to slow the development of Varroa populations and thereby reduce infestation pressure. They have the advantage of being applicable during the main beekeeping season, whereas the use of chemotherapy would entail significant risks of contaminating honey harvests.
Removal of capped drone brood: an effective biotechnical method to reduce Varroa infestation
The removal of capped drone brood exploits the well-documented preference of Varroa destructor for drone cells, which are infested approximately eight times more frequently than worker cells. This biological trait allows drone brood to function as a trap for mites. The Swiss field trial evaluated the effectiveness of this measure under local conditions and assessed its necessity within a control concept based solely on autumn formic acid treatments. :contentReference[oaicite:4]{index=4}
Approximately twenty Dadant Blatt colonies were divided into comparable test and control groups. In the test group, a dedicated drone frame was inserted at the edge of the brood nest at the end of March. Capped drone brood was removed regularly once at least 1 dm² was sealed. Control colonies received no such intervention. Parameters recorded included the number of removed drone cells, mites contained within them, natural mite fall, efficacy of subsequent formic acid treatments, colony development and honey yield.
In 1993, favourable conditions allowed an average of 4.2 removals per colony. On average, 3,374 capped drone cells were removed per colony, containing 788 mites. From May onwards, natural mite fall diverged markedly between groups. After late-summer formic acid treatments, mite populations in treated colonies were 3.5 times lower than in controls. Several untreated colonies exceeded 5,000 mites, with visible symptoms such as deformed wings.
In 1994, with less favourable weather and only 2.3 removals per colony, the effect remained significant: control colonies harboured more than twice as many mites as treated colonies. Thus, even limited drone brood removal effectively slowed Varroa population growth.
No significant negative impact was observed on honey production, colony strength or total worker brood production. Concerns that the method might select for mites preferring worker brood were considered unfounded, as worker brood remains the dominant reproductive substrate throughout the year.
However, drone brood removal alone does not replace acaricide treatments. It functions as a complementary biotechnical measure that suppresses mite population growth in spring and early summer, enabling safer timing of autumn treatments. Early introduction of the drone frame, continuous placement adjacent to the brood nest and strict removal before emergence are essential.
In conclusion, capped drone brood removal is an effective and colony-safe component of integrated Varroa management, significantly reducing infestation pressure when combined with appropriate autumn treatments. :contentReference[oaicite:5]{index=5}
See also:
- Varroa destructor
- Practical Guide 1.2.5: Formic acid strips (Formicpro®)
- Integrated varroa control throughout the season
- Everything about swarming