Promoting sustainable beekeeping and genetic diversity through drone comb trapping

Drones: The Forgotten Bees. Exploring the use of drone comb traps to fight varroa mites and improve genetic diversity in open-mated queens.

Honey bee drones (males) are being ignored by bee keepers as they focus on mite control and queen rearing. In this project, drone brood trap frames will be removed from honey production hives as a proven, non-chemical means to control mites during the spring and summer months. Instead of killing the drones like most methods suggest, capped drone frames will be moved into special drone rearing colonies so they can emerge as adults, saturate the local area, and potentially lead to better genetic diversity through open-mated queens.

Introduction:

Varroa destructor mites emerged as a serious problem for beekeepers in the 1980’s.  Now roughly three decades later, they continue to threaten the survival of bee populations (managed and feral) as well as the pollination dependent crops. Mites induce stress for honey bees and are a vector for many diseases attributed to colony losses.  Between 1948 and 2010, the number of producing colonies in the United States declined from 5.9 million bee hives to 2 million (USDA NASS).

Currently, all chemical miticide treatments negatively impact drone production.  Initially the chemical approach was an application of moderately toxic pesticides; Apistan (fluvalinate) and Checkmite (coumaphos). Although very effective, issues surrounding their use compounded; mites developed resistance, chemical traces were found in wax, queen rearing was impacted, drones were not surviving, and those drones that did survive had reduced sperm production.  Naturally occurring Thymol and Menthol also created post-treatment drawbacks with significant reductions in brood.  Mite Away Quick Strips containing formic acid were recently approved and unlike other treatments can be used during honey production.  Formic acid is the same naturally occurring chemical ants emit for defense.  Unfortunately, colonies treated with formic acid remove drone eggs and delay production of new drones.  Thus, although reported as safe, it results in half as many drones and occasionally a reduced worker brood population. 

Drone brood trap frames, on the other hand, are an effective non-chemical mite control method.  Yet again, the drones are also destroyed.  Research into the varroa mite’s reproductive cycle show female mites favor drone brood as a host for their eggs.  While drones are in the capped stage of development, immature mites feed off of the drone pupae’s blood.  Drones are favored because their cells remain capped an average of 2 days longer than a worker, and 6 days longer than queens.  This gives the female mite, who lays singular eggs in 30 hour increments, an opportunity to lay more eggs thus increasing the mite population an average of 1 to 2 more mites per cell.  With a potential of 8000 total cells on one frame of comb, 8000 to 16,000 more mites are possible in a frame of drone brood versus worker brood.  Because of this biological anomaly, beekeepers have turned to natural control efforts that trap mites in drone comb. Such efforts typically involve this comb being frozen, scraped out, or shocked with electricity.  Models supporting this method have predicted that reducing drone brood by 1% would reduce mite populations by as much as 25%. Once more, although very effective, drones are sacrificed.

Some mite control methods have been implemented which do not impact drones;  powered sugar dusting as a means to encourage bees to groom each other, screened bottom boards to keep fallen mites from returning to the colony, and local survivor queens genetically chosen for mite resistance are such examples.  Among these, queen rearing through high-end breeders and local micro-breeders is the best natural, long-term option.  This promotes bees that can deal with mites on their own accord.  There is just one problem; how do we pass on all improved genetics?

Mite resistant, survivor queen programs can be found in each of the Northern States where genetic lines are being developed with  both hygienic (cleaning out worker cells with mite infestations but not drone cells) and grooming behaviors (removing mites from the external surface of the bee).  Oddly, with all this attention to genetics, little effort has been given to drones whose sole task is to pass on genetic material.  This is easily evidenced by the amount of equipment found for sale in beekeeping catalogs for queens versus drones.  Most beekeepers concentrate on keeping hives alive for honey production and perceive drones as resource consumers – they eat, mate, and die. However, efforts to control mites by killing drones or making them infertile goes against the genetic progression being made in mite-resistant bees.  This oversight may very well result in more severe problems.  Unfortunately, solving this problem requires beekeepers to think differently and change some longstanding methods.

Genetic diversity is very important to honey bees.  It helps prevent infections, reduces the chance of non-viable drones being produced, and creates a hive of worker micro-colonies with diverse specialties based on the drone’s genetics.  Yet for this to happen, a queen must be able to mate with drones from different colonies; the number of different drones mated with averages 13; the total sometimes reaching 26.

Drones are created when, under many varying conditions, the queen lays an unfertilized egg in a larger sized cell. Being haploid, they only bring one allele with them from their mother.   If the drone’s mother (the queen) is a respected line, the male needs to be given the opportunity to mature, mate, and share his genetics (which is also the same as the queens) with other colonies as well.  By killing drones or making them infertile, the potential for bees to naturally evolve to adapt to mites is also being lost.