By Elizabeth M. Walsh, Ph.D.
Honeybees (Apis mellifera) are the most important managed insect pollinators in agricultural crop systems in the United States and Canada. However, annual colony mortality rates over the past 15 years have consistently exceeded historical records. Because honeybees are eusocial generalist pollinators and easy to manage, they offer a unique opportunity to investigate a wide range of questions at molecular, biological, and ecological scales. As the Anthropocene progresses and honeybees face rapidly changing land uses coupled with climate change and other threats, future research to mitigate the impacts of these factors is essential to increase honeybees' ability to fight for themselves, discover practical mitigation methods, and achieve stabilization of the health of the insects that have structured agricultural ecosystems.
Members of the American Association of Beekeepers (AAPA) and the Canadian Association of Beekeepers (CAPA) have contributed greatly to research efforts on honey bee biology, both at the basic and applied science scale. AAPA and CAPA have collaborated to publish a special issue in the Journal of Insect Science that brings together recent research conducted by members of both organizations. Specifically, the journal brings together Canadian and American research that addresses honey bee health in terms of 1) abiotic and biotic stressors, and 2) potential stress mitigation methods.
Key findings from the studies in the collection are highlighted below: See a detailed overview in the collection's introduction, click below to read the individual studies, or view the full collection of over 24 papers from the Journal of Insect Science for free: “Current honeybee research: exploring micro- and macro-aspects of health and sociobiology”
Abiotic and biotic honey bee stressors
Potential ways to reduce stress
In a study of different applications and treatment intervals, oxalic acid evaporation every 5-7 days was the most effective. Contrary to anecdotal recommendations in the beekeeping industry, applying glycerol oxalate to colonies with shop towels was not an effective method for Varroa mite control in the southeastern United States. Oxalic acid evaporation was about five times more effective when beekeepers induced larval resting in colonies during application. A new compound for Varroa mite control, 1-aryloxy-4-propoxybenzene, demonstrated 78.5% efficacy against Varroa mite with minimal adverse effects on honeybees and is expected to continue to be developed. Amitraz-based treatments combined with thymol-based treatments were particularly effective for Varroa mite control in the southeastern United States, but the reduction in honeybee populations after combined treatments requires further study. Treatments that delay Varroa mite re-emergence for 2-6 months in winter and spring were not always effective when applied in summer and fall in Florida. Natural chemical-based treatments can be used throughout the summer in eastern Canada to substantially reduce Varroa mite levels, but not Varroa mite-associated virus levels. Highly groomed honeybees discriminate between triggers of grooming behavior. Highly groomed honeybees responded strongly to Varroa mites and less to chalk dust, suggesting previously unknown subtle differences in grooming behavior. The anthranilic diamide chlortraniliprole was effective in preventing infestations of dwarf hive beetles in laboratory tests and small-scale field trials in the southeastern United States, and may enable a new chemical treatment for dwarf hive beetles. The method of managing honeybee colonies indoors allows laboratories to continue experiments through winter in temperate regions, but may affect the learning and thermoregulatory behavior of honeybees. Different essential oils and propolis extracts influenced the lifespan and gut microbiota abundance of individual honeybees, with some oils and extracts affecting genes related to nutrient assimilation and detoxification. Essential oils such as lemongrass, spearmint, and propolis are beneficial for honeybee health, with the caveat that thymol and other substances that may not have been investigated are more toxic than beneficial at field use levels. Two probiotic formulations, Bactocell and Levucell, increased larval levels in honeybee colonies in spring, but did not reduce gut parasites such as spore abundance of the genus Vairimorpha (formerly Nosema). Individual and in vitro studies of probiotic use show promise in improving honeybee disease resistance, but so far there is a lack of evidence in bee colonies or in the field to make the best management decisions. A survey of beekeepers in Pennsylvania from 2017 to 2022 found that control of Varroa mites was the strongest predictor of honeybee colony survival. Beekeepers who tried to replace queens in healthy colonies by placing queen cells in honey boxes had only a 6% success rate, but queen replacement may still be an effective method if the colony is already weakened. Profit modeling based on data from beekeepers in British Columbia found that compensating for colony losses with packages was less profitable than splitting colonies, and that beekeeping operations that diversified their income streams were generally more profitable than those that did not.
Dr. Elizabeth M. Walsh is a research scientist in the Honey Bee Breeding, Genetics and Physiology Unit of the USDA Agricultural Research Service in Baton Rouge, La. Email: Elizabeth.M.Walsh@usda.gov.
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