Found in Translation

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Found in Translation

When is it Time for a Comb-Over?
By: Jay Evans, USDA Beltsville Bee Lab

In December 2024, veteran beekeeper Bob Binnie gave the American Honey Producers Association an update on his learned belief that rotating out comb from his operation is critical for healthier, more plentiful bees. He started on this path after reading a 2001 paper by Jennifer Berry and Keith Delaplane that followed colonies for three (!) years and showed better brood patterns across years in colonies built around new wax versus darkened wax of an indeterminate but substantial age (Berry, J. A., & Delaplane, K. S. (2001). “Effects of comb age on honey bee colony growth and brood survivorship”. Journal of Apicultural Research, 40(1), 3–8, https://doi.org/10.1080/00218839.2001.11101042). This made me wonder about the state of the art for this question, since it has surely been on the minds of beekeepers and researchers for a while. Several recent papers have reinforced the need to remove old comb, whether to reduce pesticide residues or infectious microbes, while also exploring means to redeem used comb, or at least wax, as a safe component of hives.

Megan Colwell from the University of Manitoba devoted her PhD work to a set of clever experiments aimed at assessing the movement of harmful viruses from diseased bees into frames of comb and then back out into bees of later generations (Colwell, M. “A study on novel transmission routes of honey bee (Apis mellifera L.) viruses with a focus on the epidemiological role of wax comb”, 2022, University of Manitoba). A practical outcome of this work was to see what beekeepers might do, aside from constant comb rotation, to reduce the impacts of lingering viruses. She found that comb from deadout colonies that was left to rest for 30 days showed a substantial (20-50% depending on the virus) decrease in virus levels (Colwell, M.J., Pernal, S.F. Currie, R.W. (2024) “Treatment of waxborne honey bee (Hymenoptera: Apidae) viruses using time, temperature, and electron-beam irradiation.” Journal of Economic Entomology117:34-42. doi:10.1093/jee/toad216). Surprisingly, the temperature at which combs were stored did not matter much across the tested range, which covered climatic extremes in Manitoba (from -20oC to +20oC). In addition, the use of expensive ‘e-beam’ irradiation only marginally reduced virus levels in treated comb compared to control comb that went on the same 4600 km round trip to the radiation bank but was not subjected to radiation. All tested comb tended to hang onto at least some viruses, as assessed by genetic tests for the integrity of viral RNA genomes. So, is a 20-50% reduction of pathogens over time a sign your dead-out combs are safe? Maybe so for viruses, where the goal is not to eliminate them from the colony (impossible) but to lower disease by reducing the contagious surfaces encountered by future bees. This is the logic behind wiping deck chairs with bleach between cruises to reduce future cases of norovirus; somebody’s auntie is still going to get sick, but hopefully a higher proportion of guests will have a pleasant cruise and enjoy the buffets. Regardless, it is promising that viruses show some decay over a matter of weeks, but this work suggests that more can be done to accelerate this decay.

To that end, David Saleh and colleagues tried to knock out viruses by heating colony food resources to more extreme temperatures of 70oC (158 degrees Fahrenheit) for one hour. Importantly, while most studies have used RNA integrity as a measure for viral infectivity, this study went an extra step by inoculating healthy bees with viral soups rescued from treated hive stores (fresh pollen and bee bread). Extreme temperatures did the trick, almost completely killing viral activity in hive stores. Such high temperatures will melt wax, so these researchers also tested heat treatments just below the wax melting point (at or below 60oC). They achieved decent inactivation of viruses at 60oC (over 97% inactivation after one hour), suggesting that a heat pulse just below melting temperatures could work for sterilizing entire frames (Saleh, D. S., Story, C. M., Palmer, W., Ha, G. J., Madella, S., Ryabov, E. V., & Corona, M. (2024). “Deformed wing virus in bee bread: infectivity and thermal inactivation”. Journal of Apicultural Research, 63(4), 711–720. https://doi.org/10.1080/00218839.2024.2357448).

As beekeepers know, both miticides and crop-protection pesticides can also accumulate in wax and impact bee health. In the miticide class, wax contaminated with the organophosphate coumaphos has been shown to impact queen and drone health. This fact, coupled with the high absorbance of coumaphos into beeswax, means that this once-vital but rarely used mite treatment is still found in older comb at worrisome levels. Rogan Tokach and colleagues at the University of Nebraska recently embarked on a study to try to quantify the impacts of comb containing high pesticide residues on the abilities of colonies to raise emergency queens. This work was precipitated by an extreme observation: a bee yard near the University’s Extension Research Facility that simply could not sustain bee life over multiple years thanks to unusually high usage of crop pesticides. The researchers established nucleus colonies with one frame of foundation and two frames of drawn comb containing pollen and honey. These drawn frames came from either control colonies in good health or colonies that had died in prior years in the yard with acute pesticide poisoning. They added a fourth frame, containing eggs, into each box along with 3 ½ pounds of worker bees and then waited for those workers to seize the day by rearing emergency queens. Successful queen replacement occurred in 84% of the control colonies and only 33% of colonies carrying contaminated comb and food stores, indicating a longterm effect of accumulated pesticides (Tokach, R.; Smart, A.; Wu-Smart, J. (2023) “Re-using food resources from failed honey bee (Apis mellifera L.) colonies and their impact on colony queen rearing capacity.” Scientific Reports 13. doi:10.1038/s41598-023-44037-2). Their analyses suggest that pesticide impacts came from stored pollen consumed by nurse bees as they raised brood.


To help address this potential problem, Christina Kast and colleagues sought ways to cleanse and reuse wax from contaminated frames. First, they confirmed that a diverse set of pesticides found in pollen were readily absorbed by wax. They then tested both heat and a water rinse as means of removing embedded pesticides prior to producing new foundation. While melting wax and suspending it briefly in water was enough to decrease levels of water-soluble neonicitinoid pesticides, this process unfortunately had little effect on the majority of tested pesticides (Kast, C., Müller, J. & Fracheboud, M. (2024) “Temporal entry of pesticides through pollen into the bee hive and their fate in beeswax.” Environ Sci Pollut Res 31, 61060–61072. https://doi.org/10.1007/s11356-024-35224-3). A more advanced way to purify wax involves using the solvent methanol during the melting process to truly liberate wax from most accumulated chemicals. José Manuel Flores and colleagues confirmed this reduction in chemicals but worried that bees would notice and shun recently stripped wax. While it took an extra day for queens to start laying on comb drawn from treated wax, once they started doing so colonies produced at equal rates. This suggests that methanol treatment during wax rendering might indeed be a safe way to return beeswax to a more pure state (Flores, J.M.; Luna, A.; Rodríguez Fernández-Alba, A.; Hernando, M.D. Acceptance by Honey Bees of wax decontaminated through an extraction process with methanol. Insects 2023, 14, 593. https://doi.org/10.3390/insects14070593).

The ghosts of past threats need not ruin your use of combs, even from deadout colonies. For now, the recommendation remains to rotate out comb every few years, depending on cycles of brood and colony exposure to high levels off pesticides. To combat viruses after a colony loss event, letting combs sit for at least 30 days seems advisable, longer if you can keep them safe. This is, of course, not advisable for colonies with any signs of AFB, which should be discarded, and the jury is still out on the benefits and scale of a ‘time out’ needed after symptomatic EFB. Combs from colonies facing an acute pesticide event should probably be taken out of circulation completely unless you have access to advanced wax purification with methanol or another solvent that will pull wax-loving chemicals free. Meanwhile, do what you can to manage disease and exposure to pesticides. This will give your bees and their homes one less thing to worry about.