Drones get a bad rap. The male of the species is often viewed as ‘lazy’ and inconsequential when compared to the critical roles played by the queen or worker bees. When facing the devastating effects of varroa mite infestation, the opinion that drones are not so important has led to the varroa control method known as ‘drone brood removal’. Though not without some merit, drone brood removal is a short-sighted solution to a long-term issue. What drones bring to the table is essential not just for survival of the colony, but for the species.
What is the big idea?
The male of the species has one main job. Drone bees are to mate with the queen. They are larger than worker bees, with long abdomens and distinct eyes. Drones also have a longer development time of 17 to 19 days in the capped brood cell, as opposed to the worker bees who are in the cells for only 12 days. As varroa also reproduce in the capped brood cells, the longer development time means that the possibility for female varroa mites to be mated with, is much higher. Where an infected drone cell allows 2-3 mated female mites to survive, a worker bee cell only allows 1.7 mated female mites to survive. And the more mated mites you have, the worse your varroa infestation.
Beekeepers are left to weigh up the contributions that drones make to the colony, against the devastating effects of the mite. And as a lot see strong drone populations as inconsequential, they are opting to remove drone brood in early spring, so as to reduce the development of the varroa mites.
But here is the catch. Queen mating mainly takes place from late April to June. Beekeepers who remove drone brood too early severely reduce the available males for mating, and therefore the selection of the fittest.
Why is that a problem?
Each hive needs a certain population of males (2000 – 6000) to be healthy, as developed males are responsible for the fertilization of the queens. A good mixture of males at the drone congregation area (where the mating of the queen takes place) helps to spread different genetic information. This brings genetic diversity to the species, which is key to survival and adaptation.
For queens, there is an additional biological benefit. Queens that have mated with a selection of strong, diverse males have fully loaded ’spermathekes’ and are far more likely to have lifespans of more than 1 year in a hive. An issue for many beekeepers is the diminishing lifespans of queens. Where beekeepers in the past would replace queens every 2-3 years, they are nowadays often having to replace queens on a yearly basis. As with everything in beekeeping, this cannot be accredited solely to fewer mating partners. However brood removal, when coupled with the spread of virus´s caused by varroa, certainly makes queen loss worse.
Drone brood removal is often applied alongside other varroa control treatments, like formic acid. This presents a very specific threat, as formic acid is directly linked to heavy queen losses. If a queen dies early in the season due to formic acid treatment, the hive will immediately start building a new queen cell, which needs to be mated by mid to late August once matured. If there is no longer a strong population of drones, there may not be sufficient partners for the new queen. Next spring these queens will suddenly stop creating eggs, but as they are still in the hive, the hive will not develop during early spring. This means weaker colonies that cannot pollinate the surrounding areas in this short and crucial time. To make matters more dire, climatic changes are forcing pollinators to be ready earlier each year.
All biological systems are dependent on multiple factors, and while we are learning more and more all the time, we do not yet understand these factors. As beekeepers, our approach is to apply the lightest touch as possible, especially when chemicals, or human actions such as brood removal are involved. Removing drone brood may be an easy fix to a difficult problem. It may even be necessary to save the colony, but tread lightly, as the consequences are felt in other areas such as queen losses and less genetic diversity in the colony. Mites are a very real and also quite new problem (in evolutionary terms) for honey bees. Their biology has not yet had the time to evolve natural defenses. This is where we can help, but we still should always keep as close to nature as possible.