2021 National 4-H Beekeeping Essay Competition
Topic: Immunity: Threats to Bee Colonies and Methods to Defend Against the Threats
Ocean County 4-H, New Jersey
Varroa, American Foulbrood and the Amazing Honey Bee
Albert Einstein is quoted to have said “If the bee disappeared off the face of the Earth, man would only have four years left to live.”1 Bees are vital for the preservation of ecological balance and biodiversity in nature.2 The Western honey bee (Apis mellifera) provides one of the most pivotal of ecosystem services, pollination, and makes food production possible. The annual global production of food that depends directly on pollination is worth between $235 and $577 billion.2 A third of the world’s food production depends on bees, i.e. every third spoonful of food depends on pollination.2 Unfortunately, the future of bees and the future of dependent agricultural economies are in jeopardy.
The greatest single contributor to the decline of honey bee health is the Varroa destructor mite.3,4 Varroa is an ectoparasitic mite that exploits the honey bee’s lifecycle.3,4 A single Varroa can shorten the lifespan of a bee by one-third, and two mites can shorten it by one-half.3-5 It feeds on the fat bodies of developing larvae and adult bees and aggressively reproduces within an infected colony.3 By weakening and ultimately killing colonies by out- reproducing their host, Varroa is a primary cause of colony collapse disorder.5 Furthermore, Varroa facilitates the transmission of multiple viruses, including Deformed Wing Virus (DWV), and other diseases which may lead to honey bee mortality.4,5
To control the spread of Varroa, beekeepers initially used acaricides, pyrethroids, and organophosphates pesticides.4,5 Unfortunately, these chemicals have been found to increase the early replacement of the queen, heighten mortality in adults and brood, reduce body weight in queens, decrease the amount of lipids, carbohydrates and proteins in workers.2,5 Furthermore, these compounds have also been found to accumulate in the beeswax which impacts the development of bee larvae.5 The frequent use of these synthetic miticides to control Varroa has resulted in the development of resistance to many of the chemical components of these miticides.1,2,5 Likewise, the excessive or improper use of synthetic compounds has also resulted in the contamination of hive products which pose a health risk to both bees and human consumers.5
Another major threat to colony health is American Foulbrood (AFB); a transmissible and lethal bacterial disease of honey bee brood that is found worldwide. AFB is caused by the spore forming bacterium Paenibacillus larvae.6 Infections affect most of the brood, severely weakening the colony and eventually killing it. Although AFB is not highly contagious, bacterial spores can easily be spread between hives and apiaries through the exchange of equipment and movement of infected combs.6 Adult bees are not affected by AFB but can spread spores within and between infected and clean hives through robbing and drifting.6 AFB spores can remain viable for over 50 years and are resistant to freezing and high temperatures.7
Within a colony, spores are spread by nurse bees performing in-hive tasks, such as cleaning and the feeding of young larvae with spore-contaminated food.8 Billions of spores are produced in the dying larvae.8 Furthermore, in the nurse bees attempt to clean away the diseased pupae, they become carriers for the disease and further infect new young larvae when they feed them.8 The traditional control measure for American Foulbrood is to exterminate all bees in an infected colony by burning all dead bees and hive materials, particularly the wax comb.6,8
Specifically, to combat Varroa and AFB, researchers have been studying the instinctive hygienic behavior of bees.9,10 Hygienic behavior is the detection, uncapping, and removal of diseased brood from the hive.9 It is most commonly observed in worker bees aged 15 to 20 days.9 Bees with this recessive trait are able to detect and physically remove disease-infected brood from the colony.9 Hygienic bees have been shown to have an acute sense of smell for the odor of diseased brood.10,11 Since they are able to detect and remove diseased brood before the human eye can detect any sign of disease symptoms, it prevents the disease from spreading throughout the colony.10 Hygienic behavior against Varroa and AFB is an important defense that bees have during the long period in winter when there is no brood nest. Colonies with a high frequency of hygienic behaviors can reduce the weakening and mortality of worker bees during winter before the new reproductive season begins.10,11 Selective breeding for the naturally occurring social immune trait of hygienic behavior has emerged as an sustainable approach in beekeeping.11
Accumulating evidence also suggests the importance of the gut microbiota of bees for overall honey bee health.12-14 The bee microbiota is responsible for converting dietary compounds in the gut, enhancing sucrose responsiveness, and stimulating the immune system.12 The type and amount of nutrients (pollen and nectar) available during the foraging season also influences the composition of the gut microbiota.12 During spring, summer, and autumn, young worker (nurse) bees stay inside the hive to care for larvae and feed on nutrient- rich pollen, whereas older worker bees become foragers that feed on nectar and honey to fuel their energy-expensive flights.13 In late autumn, newly emerged adult worker bees become winter bees with an extended lifespan (~6 months) to help ensure colony survival during the cold winter season.14 These bees are responsible for thermoregulation inside the hive and feed strictly on food stores (pollen, beebread, and honey) as well as retain their feces all winter which affects their gut microbiota.12 Researchers are currently investigating the gut microbiota of winter bees to understand the physiological adaptations of honey bees to survive the winter season.12,15
Pollinator health is a top priority, both ecologically and economically significant. Honey bees are the most agriculturally important pollinator worldwide. Because bee colony losses typically occur during the winter months, winter bees are highly critical for colony survival.12 By understanding the factors influencing the health status of winter bees; including hygienic behavior and the gut microbiota, the effects of Varroa and AFB may one day be alleviated by helping honey bees help themselves. In the end, whether it is survival or extermination, the health of honey bees will have profound consequences, from flower to farmer to fork.
Word Count: 1,000 words
Hygienic removal by adult worker bees of pupae infested with Varroa mites. October 2020.
Rodgers, P.(2014). Einstein and the Bees: Should you worry? Forbes. Available at: https://www.forbes.com/sites/paulrodgers/2014/09/09/einstein-and-the-bees-should-you- worry/?sh=441364178157
- World Bee Day (2020). The Importance of Bees. Available at: https://www.worldbeeday.org/en/about/the- importance-of-bees.html
- Ramsey SD, Ochoa R, Bauchan G, et al. (2019). Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph. Proceedings of the National Academy of Sciences Jan, 116 (5) 1792-1801. Available at: https://www.pnas.org/content/116/5/1792
- Hunt G, Given Purdue University: Beekeeping: What Beekeepers Should Know About Bee Mites. Available at: https://extension.entm.purdue.edu/publications/E-201/E-201.html
- Ellis JD, Zettel Nalen. University of Florida: Varroa Available at: http://entnemdept.ufl.edu/creatures/misc/bees/varroa_mite.htm
- USDA Agricultural Research Service. US Department of Agriculture. American Foulbrood Disease. Available at: https://wwars.usda.gov/northeast-area/beltsville-md-barc/beltsville-agricultural-research-center/bee-research- laboratory/docs/american-foulbrood-disease/
- American Foulbrood. Available at: https://beeaware.org.au/archive-pest/american-foulbrood/#ad- image-0
- Snyder R. American Foulbrood (ABF). Available at: https://beeinformed.org/2013/10/21/american-foulbrood- afb/
- Spivak M, Reuter GS (2001) Resistance to American foulbrood disease by honey bee colonies, Apis mellifera, bred for hygienic behavior. Apidologie 32: 555-565. (Apidae: Hymenoptera). J. Econ. Ento-mol. 91: 64-70.
- Kaira M Wagoner, Marla Spivak, Olav Rueppell. (2018). Brood Affects Hygienic Behavior in the Honey Bee (Hymenoptera: Apidae), Journal of Economic Entomology, Volume 111, Issue 6, December, Pages 2520–2530,
- Mendel (2020).Hygienic Bees Smell Disease and Do Something About It. How Hygienic Behavior in Honey Bees Influences Colony Health. Available at: https://backyardbeekeeping.iamcountryside.com/health- pests/hygienic-bees-smell-disease/
- Kešnerová, , Emery, O., Troilo, M. et al. (2020).Gut microbiota structure differs between honeybees in winter and summer. ISME J 14, 801–814.
- Raymann K, Moran (2018). The role of the gut microbiome in health and disease of adult honey bee workers. Curr Opin Insect Sci.;26:97–104.
- D’Alvise P, Böhme F, Codrea MC, Seitz A, Nahnsen S, Binzer M, et (2018).The impact of winter feed type on intestinal microbiota and parasites in honey bees. Apidologie.;49:252–64.
- Trager (2020).Chemistry World:Tweaking honey bee bacteria to fight colony collapse disorder. Available at: https://www.chemistryworld.com/news/tweaking-honey-bee-bacteria-to-fight-colony-collapse- disorder/4011119.article
Kaitlyn Culbert 2219 Longest Drive
Kaitlyn Culbert attends Toms River High School North in New Jersey. She first became interested in bees through a research contest sponsored by the Army Educational Outreach Program (AEOP) regarding pollinators. After coming in first place at AEOP, Katie decided to implement a research project involving Varroa mites and essential oils. She contacted local and state beekeeping clubs and beekeepers, researchers at Rutgers, Stockton, and the University of Florida, as well as commercial beekeepers to help her finalize her research project. Her research entitled, “Breakthroughs in Honey Bee Health: Continuous-Release Mist Diffusion of Thymol-Based Essential Oils” earned her First Place, Environmental Sciences at the Rutgers Junior Science and Humanities Symposium (JSHS) in March 2021. Most recently, Katie also earned First Place, Environmental Sciences at the Delaware Valley Regional Science Fair (DVSF) in April 2021. In the fall, Katie hopes to implement a field study of her Varroa and essential oils research. In the meantime, she completed her basic beekeeping certificate. Katie is also the Founder and Student Leader of the first beekeeping club at Ocean County 4H. When not involved with bees and beekeeping, Katie is also a competitive swimmer and is active in her high school Math, Robotics, and Bible Study Clubs.