July 2024, The Ohio State University, Entomology Department received a phone call regarding an ‘Africanized honey bee’ colony from a Hamilton County beekeeper. The beekeeper bought a few feral colonies from another beekeeper and experienced one of the colonies being more ‘aggressive’ than the others. He concluded that these were ‘Africanized honey bees’ aka’ killer bees’, put a net around the colony preventing their escape, and sent us a few dozen bees for identification. After he sent the specimens to us, he killed the colony!
Suspected ‘Africanized honey bees’ sent by the beekeeper.
There are 7 species of honey bees (Apis spp) worldwide. The western honey bee (Apis mellifera) is the most well-known for its role in honey production and agriculture. The only other domesticated bee is the eastern honey bee (Apis cerana) native to south and southeast Asia.
While only the genus Apis includes true honey bees, other bee species have been managed for honey production. Stingless bees from the genus Melipona are widely managed in the neotropics. A few other stingless bees in the genus Tetragonula, described from Sri Lanka (Silva et. al. 2018), have been managed for centuries to nest inside clay pots to allow the collection of honey that is particularly important in ayurvedic medicine (Nahala et. al. 2023) These bees have unique adaptations and behaviors that make them important in their respective ecosystems and for local honey production.
Western honey bees
The common name, ‘honey bee’ in the United States refers to the single species, Apis mellifera, which was introduced in early 1600, and is now called the ‘western honey bee’.
It is believed that the species A. mellifera originated in Africa and Asia (Frazier et. al. 2024), and it has been managed for the production of beeswax and honey and, more recently, for pollination activities. Human activity has moved this species throughout the world, except in Antarctica. There are 6 subspecies of A. mellifera recognized in the United States and Canada, namely the German black bee (Apis mellifera mellifera), the Spanish honey bee (Apis mellifera iberiensis), the Italian honey bee (Apis mellifera ligustica), the Carniolan honey bee (Apis mellifera carnica) and the Caucasian honey bee (Apis mellifera caucasica). Being subspecies, all of these bees can successfully interbreed and the US population of bees shares a mixed genetic background. In this article, WHB refers to all the western subspecies of A. mellifera.
African honey bees
In Africa, there are 12 subspecies of A. mellifera that have been recognized so far. One of the subspecies is A. mellifera scutellata, commonly known as the East African lowland honey bee, found in southern and eastern regions of Africa.
African HB colonies have a higher rate of colony growth, reproduction, and swarming (Winston et. al, 1983). For these reasons, as well as Western HBs' failure to adapt to tropical regions, led Brazilian scientists to import African HB to Brazil in 1956 to improve honey production.
Somehow, a few queens escaped and mated with local European drones in Brazil and produced a hybrid, now called the Africanized HB. In this article, the original population of A. mellifera scutellata will be called African HB and the hybrid population present in the New World, will be called Africanized HB.
After the escape, the hybridized African HB population in Brazil gradually expanded into northern parts of the Americas, arriving in the southern US in 1990. However, there is no pure African HB that can be found in the population currently, and it is virtually impossible to distinguish WHB from Africanized HB without genetic testing or rigorous morphometric analysis.
Defensive behavior of African honey bees
Frazier et. al. (2024) found that the environmental conditions in which African bees evolved are completely different from the environment in Europe where WHB evolved. Environmental pressures, pests, human honey hunters, animal predation and wet and dry seasons have played a significant role in the evolution of the African HB compared to temperate-evolved WHB. Research reported that African HB responds more quickly when disturbed and sends out 3-4 times more workers than WHB (Winston et. al, 1983).
Considerable variation in behavior and biology has been found within the African HB. For example, colonies within the same apiary range from docile to aggressive and it can be difficult to make a clear-cut definition to analyze these behaviors. Also, there are significant differences in the hygienic behavior of African HB colonies in two different locations in Kenya, and swarming patterns varied within and among the Ethiopian subspecies.
Also, there is frequent inaccurate identification of African subspecies, raising the question of the validity of some research findings Frazier et. al. (2024).
Africanized bees can be gentle over time!
In 1994, Africanized HB arrived in Puerto Rico and hybridized with the WHB population. In 2017 a study published by Avalos et. al. found a drastic reduction of the aggressive behavior of Puerto Rican Africanized HB populations within 12 generations (1994-2006). This rapid evolution of ‘gentle behavior’ was observed based on genomic analysis and the forces involved in driving the evolution of these bees are challenging to determine, but, they propose three factors, i.e. negative human-honey bee interaction, geographic isolation, and low levels of predation on honey bee colonies may have driven selection against honey bee aggression in Puerto Rico within a short period of time, which is the only place in the new world where gentle Africanized HB have evolved.
Identifying Africanized bees using forewing measurements.
Using worker bees, an attempt was made to identify the probability of Africanization for the bees sent by the Hamilton County beekeeper, using the ‘Fast Africanized Bee Identification System (FABIS) developed by Sylvester & Rinderer, (1987). The FABIS process is quick, and simple and can be used to screen large numbers of bees in a short period of time. This method has been tested in Africanized and European colonies and the accuracy has been verified.
The process FABIS method involves morphometric analysis using fresh weight or dry weight of the bees, forewing length, and hind femur length. In our case, average forewing length alone was enough to determine whether the bees provided were Africanized or not.
The FABIS method starts with the forewing length to determine the probability of Africanization. Any beekeeper in Ohio can easily adapt this method with a good microscope, a set of forceps, glass slides and a millimeter ruler.
The forewings of 10 bees were extracted at the base of the wing and the exact measurement was taken under a microscope using a calibrated ocular micrometer. If you do not have an ocular micrometer, you can use a ruler placed beside the wing and carefully measure the wing using the precise points, to the nearest 0.5 mm (see the arrows of the image below).
The average length of the forewing of our sample was 9.27 mm
This table from the FABIS method, shows the ‘Critical value measurements’ of the forewing length.
According to the FABIS table, the critical value of the wing measurement of an AHB is 9.001 mm, but the average of the 10 bees in our sample value was 9.27 mm, so the sample of bees sent by Hamilton County beekeeper is a Western HB, not an Africanized HB. What the Hamilton County beekeeper observed was an aggressive colony of WHB.
Myths and facts about Africanized honey bees
While Africanized honey bees can display more defensive behavior, aggression varies widely among individual colonies. Factors such as environment, management practices, and breeding play a significant role in their behavior.
Like other bees, Africanized honey bees usually only become aggressive when they feel threatened. They are more likely to defend their hive vigorously, but they don’t seek out humans to attack.
Experienced beekeepers can manage Africanized bees effectively. With proper techniques, they can coexist with these bees and even benefit from their honey production.
While Africanized HB can be more resilient in certain environments, many factors influence competition among bee species. Diversity in local ecosystems is crucial for overall bee health.
References
Atlas Hymenoptera - http://www.atlashymenoptera.net/page.aspx?id=238
Avalos, Arian; Hailin Pan, Cai Li, Jenny P. Acevedo-Gonzalez, Gloria Rendon, Christopher J. Fields, Patrick J. Brown, Tugrul Giray, Gene E. Robinson, Matthew E. Hudson & Guojie Zhang. 2017. A soft selective sweep during rapid evolution of gentle behaviour in an Africanized honeybee. Nat Commun 8, 1550. https://www.nature.com/articles/s41467-017-01800-0
Collins, Anita M., T E Rinderer, J R Harbo, A B Bolten. 1982. “Colony Defense by Africanized and European Honey Bees.” Science, vol. 218, no. 4567, 1982, pp. 72–74. JSTOR, https://www.jstor.org/stable/1689218
Frazier M, Muli E, Patch H. 2024. Ecology and Management of African Honey Bees (Apis mellifera L.). Annu Rev Entomol. 2024 Jan 25;69:439-453. https://www.annualreviews.org/content/journals/10.1146/annurev-ento-020823-095359
Hepburn, H. R., S. E. Radloff. 1998. Honeybees of Africa. https://link.springer.com/book/10.1007/978-3-662-03604-4
Nahala, Maheen N. M. et al. 2023. Anticancerous Properties of Tetragonula travancorica (stingless bee) Honey on Reproductive Cancer Cells. December 2023. International Journal of Agro Nutrifood Practices 3(4):1-9. https://www.researchgate.net/publication/376686211_Anticancerous_Properties_of_Tetragonula_travancorica_stingless_bee_Honey_on_Reproductive_Cancer_Cells#fullTextFileContent
Silva, Saumya; Chulantha Prasanga; Diyes Chulantha; Prasanga DiyesInoka KarunaratneInoka; Karunaratne Jayanthi Priyankara; Edirisinghe Jayanthi; Priyankara Edirisinghe. 2018. Rediscovery of Tetragonula praeterita after 1860: An unremarked common stingless bee endemic to Sri Lanka. March 2018Journal of the National Science Foundation of Sri Lanka 46(1) DOI: 10.4038/jnsfsr.v46i1.827. https://jnsfsl.sljol.info/articles/10.4038/jnsfsr.v46i1.8271
Sylvester, H. A., & Thomas E. Rinderer. 1987. Fast Africanized bee identification system (FABIS) manual. https://www.ars.usda.gov/ARSUserFiles/60500500/PDFFiles/101-200/185-Sylvester--Fast%20Africanized%20Bee%20Identification.pdf
Winston, M. L; O. R. Taylor; G. W. Otis (1983). "Some differences between temperate European and tropical African and South American honeybees". Bee World. 64: 12–21. https://doi.org/10.1080/0005772X.1983.11097902
Winston, M.L. 1992. Killer Bees: The Africanized Honey Bee in the Americas. Harvard Univ. Press.