A Cause of or Cure for Colony Collapse Disorder?
Honeybees use pheromones, or chemical messengers, to communicate with each other and orchestrate complex but cohesive hive activities. While such chemical communication is crucial to hive function, some studies have implicated pheromones in Colony Collapse Disorder (CCD), the sudden disappearance of worker bees from a colony.
The term CCD was first used in 2006 to describe the growing worldwide phenomenon of missing bees (vanEngelsdorp et al.). In addition to threatening biodiversity, CCD has grave economic implications, as the economic value of pollination was estimated at roughly $200 billion in 2005 (Food and Agricultural Organization). Explanations for CCD and its recent, sustained rise range from disease to pesticides to pests to environmental conditions. The cause remains largely unknown and could be a combination of various factors.
Pheromones have been identified as both a possible cause of and a solution to CCD. But first, some background on the fascinating chemistry of honeybee pheromones. Pheromones are hormones secreted as liquids from glands in honeybee adults, larvae or pupae (Bortolotti and Costa). They induce behavioral responses in other bees by coming into physical contact with bees’ antennae and mouthparts, whose receptors interpret the signals. Pheromones can act in either the liquid or gas phase to induce such changes.
These signals can be categorized as releaser pheromones, which stimulate short-term, behavioral responses, or primer pheromones, which induce longer-term physiological changes in bees. Pheromones produced by brood (developing bees) and queens tend to be primer pheromones important to social dynamics within the colony, while worker bees produce mainly releaser pheromones (Bortolotti and Costa).
One such releaser pheromone is the alarm pheromone, released when a bee stings. Alarm pheromones attract other bees to the site, causing them to sting or charge in defense (Bortolotti and Costa). The “brood recognition” pheromone, in contrast, is a primer pheromone that prevents worker bees from reproducing. Produced by brood, this recognition pheromone inhibits the development of ovaries in worker bees, helping to maintain the caste system within the hive (Mohammedi et al.). The “queen signal” also helps to maintain the hive’s social dynamics. Consisting of many different pheromones, it is the main determinant of colony function. Produced by the queen, the queen signal dictates the hive’s social hierarchy by preventing the rearing of new queens, stimulating workers to perform their duties and inhibiting reproduction by workers (Bortolotti and Costa).
These queen pheromones may contribute to hive weakness and CCD, a study by Penn State University, North Carolina State University and Tel Aviv University researchers showed. The study found that inseminated, reproductively healthy queens produced pheromones most appealing to worker bees. This makes sense, given that well-mated queens generate genetically diverse, productive hives that are more likely to resist CCD. When queens are poorly mated, however, they secrete pheromones that cause workers to replace them by rearing a new queen. This process significantly reduces hive productivity, as it takes weeks for the queen to start laying eggs and even longer for those eggs to develop into working bees. Such periods of decreased productivity could jeopardize hives by decreasing their honey supplies and thereby available nutrients (Niño et al.).
A recent study by researchers at the Queen Mary University of London identifies supplemental pheromones as a possible solution to CCD, however. According to the study, adding forager pheromones to hives that prevent young bees from foraging could protect colonies from CCD. Forager pheromones dictate the rate of forager bee maturation and in doing so, help maintain a proper nurse bee to forager bee ratio. The 2015 Queen Mary University of London study examined forager bee activity, as bees are known to react to stress by foraging for pollen more frequently and for longer periods of time. When lack of nutrients, disease or other environmental factors threaten the hive, bees respond by foraging at a younger age. Researchers attached radio trackers to bees and followed their movements, finding that young foragers were much less productive than older ones. Additionally, young foragers were more likely to die when foraging. Increased foraging by younger bees therefore significantly reduced hive productivity and vitality, accelerating hive collapse (Perry et al.).
So one way to prevent this potential cause of CCD would be to add pheromones that inhibit the foraging response in young bees to hives. Such chemical manipulation would stem further hive weakening in colonies experiencing stress. In this way, the enormous power of pheromones could be harnessed to stop CCD.
Bortolotti L, Costa C. “Chemical Communication in the Honey Bee Society.”In: Mucignat-Caretta C, editor. Neurobiology of Chemical Communication. Boca Raton (FL): CRC Press; 2014. Chapter 5. Available from: http://www.ncbi.nlm.nih.gov/books/NBK200983/
Food and Agricultural Organization. “Protecting the Pollinators.” http://www.fao.org/ag/magazine/0512sp1.htm. Retrieved 2015-04-5.
Mohammedi, A et al. “Effect of a Brood Pheromone on Honeybee Hypopharyngeal Glands.” Comptes rendus de l’Academie des sciences. Serie III, Sciences de la vie 319 (1996): 769–772. Print.
Niño, Elina L. et al. “Chemical Profiles of Two Pheromone Glands Are Differentially Regulated by Distinct Mating Factors in Honey Bee Queens (Apis Mellifera L.).” PLoS ONE 8 (2013): n. pag. Web.
Perry, C J et al. “Rapid behavioral maturation accelerates failure of stressed honey bee colonies.” PNAS 2015 112 (11) 3427-3432; Web. doi:10.1073/pnas.1422089112
vanEngelsdorp, D. et al. “Colony Collapse Disorder Preliminary Report.” 5 January 2006. Mid-Atlantic Apiculture Research and Extension Consortium (MAAREC) – CCD Working Group. http://www.beekeeping.com/articles/us/ccd.pdf