Mobbed: small hive beetles are an invasive threat to bees

Small hive beetles (SHBs, Aethina tumida Murray) are native pests of African honey bee subspecies (Apis mellifera scutellata and A. m. capensis). Due their ability to survive transportation and flourish in temperate climates, SHBs are now established on several continents, including North America. In the US, the first SHB specimen was collected in South Carolina in 1996. Two years later, SHB reports were confirmed in Florida, and SHBs have since spread.1–3

SHBs do not cause extensive damage to bee hives in their native African range. Rarely seen in strong hives, SHBs concentrate their attack on weak colonies and scavenge on the remains after the hive succumbs or absconds. Nest abandonment is a common behavior in African honey bees; they abscond when overwhelmed with disease or they leave to seasonally migrate. Subject to different selection pressures, European honey bees subspecies (Apis mellifera lingustica) in North America display diminished versions of the defensive behaviors African bees use to suppress, contain and evade infestations. These behaviors include aggression towards beetles, removal of beetle eggs and larvae, herding and imprisoning beetles in propolis, and absconding.1

Adult SHBs are strong fliers. They are attracted to colony odors including honey, pollen and the scent of worker bees. After locating and entering a colony, SHBs stealthily feed on hive food stores. Adult SHBs are small and hide from bees in crevices. SHBs also escape bee aggression by running away or deliberating falling from frames. Female SHBs lay approximately 1,000 eggs in their lifetime. Females distribute small clutches of eggs throughout the hive in cracks, on pollen and even in capped bee brood. In heavily infested hives, the hatched larvae wreak havoc. SHB larvae both eat and spoil the hive's food stores. SHBs harbor the yeast Kodamaea ohmeri. Once in contact with honey and pollen, the yeast ferments the hive's food, producing a slimy mass that the bees will not eat. Structural damage to the wax comb caused by SHB larvae feeding can even cause the food to run out of the frames, fouling the colony. The strong odors emitted by the fermenting food exacerbate the infestation by attracting more adult beetles to the hive. In the US, even strong colonies can be overwhelmed, and the invading SHBs consume both the hive's ruined food and brood.1,2

After feeding, SHB larvae leave the colony and burrow into the soil near the hive's entrance to pupate. Adult SHBs emerge from the ground and seek a host colony. SHB pupation is affected by temperature and soil moisture; cold and arid conditions limit beetle pupation.1,2 In colder regions, SHBs temporarily halt reproduction and overwinter inside colonies. SHBs can produce several generations each year in warm climates.4 Favorable conditions in the southern US allow SHB populations to build, and beetles are frequently shipped to other regions of the country in bee packages. SHBs are also moved with migratory bee colonies. Due to climatic and other factors, the severity of the damage caused by SHBs varies regionally and by year. SHB damage is not limited to apiaries and can extend to honey houses and their contents. Frames removed for honey extraction can harbor SHB eggs. These hatch in the honey house, and if left unchecked, the SHB larvae spoil the honey.1,2

Interestingly, scientists recently discovered that SHBs can host several honey bee viruses, the introduced intestinal parasite, Nosema ceranae, and other gut trypanosomal parasites.5–8 The extent to which SHBs serve as reservoirs and spread these diseases, as well as whether these diseases negatively affect SHBs, is poorly understood.

The host and geographic range of small hive beetles may expand

SHBs are members of the beetle family Nitidulidae. Many Nitidulid species reproduce on rotting fruit, or their life cycles are closely connected to those of other social insect species. In laboratory experiments, SHBs successfully reproduced on fruit and in native bumble bee (Bombus impatiens) colonies.1 Commercial bumble bee colonies can also become naturally infested when placed near apiaries.9 These findings suggest that SHBs could not only temporarily survive on fruit in the absence of honey bee hosts, but also that they could successfully switch to parasitizing native bees. Bumble bees and other wild bees did not coevolve with SHBs. Thus, native bees likely lack natural defenses, and such a host expansion could be particularly damaging to bee populations.

Global warming also threatens to expand the range of SHBs. Scientists modeled current and future global climate conditions and examined their suitability for SHBs. Since SHBs flourish in warm humid conditions,4 results suggest that the range of SHBs is likely to increase.10

How can you manage small hive beetles in your honey bee colonies?

Beekeepers can take many steps to make their apiaries and honey houses less hospitable for SHBs.2 Preventative measures and treatment options are outlined in the extension article cited below.
Mid-Atlantic Apicultural Research & Extension Consortium11

References

  1. Neumann, P. & Elzen, P. J. The biology of the small hive beetle (Aethina tumida, Coleoptera: Nitidulidae): Gaps in our knowledge of an invasive species. Apidologie 35, 229–247 (2004).

  2. Cuthbertson, A. G. S. et al. The small hive beetle Aethina tumida: A review of its biology and control measures. Curr. Zool. 59, 644–653 (2013).

  3. Schäfer, M. O. et al. How to slow the global spread of small hive beetles, Aethina tumida. Biol. Invasions 21, 1451–1459 (2019).

  4. De Guzman, L. I., Frake, A. M. & Rinderer, T. E. Seasonal population dynamics of small hive beetles, Aethina tumida Murray, in the south-eastern USA. J. Apic. Res. 49, 186–191 (2010).

  5. Huang, Q., Lopez, D. & Evans, J. D. Shared and unique microbes between Small hive beetles (Aethina tumida) and their honey bee hosts. Microbiologyopen 8, e899 (2019).

  6. de Landa, G. F. et al. Pathogens Detection in the Small Hive Beetle (Aethina tumida (Coleoptera: Nitidulidae)). Neotrop. Entomol. (2020). doi:10.1007/s13744-020-00812-8

  7. Eyer, M., Chen, Y. P., Schäfer, M. O., Pettis, J. & Neumann, P. Small hive beetle, Aethina tumida, as a potential biological vector of honeybee viruses. Apidologie 40, 419–428 (2009).

  8. Cilia, G., Cardaio, I., dos Santos, P. E. J., Ellis, J. D. & Nanetti, A. The first detection of Nosema ceranae (Microsporidia) in the small hive beetle, Aethina tumida Murray (Coleoptera: Nitidulidae). Apidologie 49, 619–624 (2018).

  9. SPIEWOK, S. & NEUMANN, P. Infestation of commercial bumblebee (Bombus impatiens) field colonies by small hive beetles (Aethina tumida). Ecol. Entomol. 31, 623–628 (2006).

  10. Cornelissen, B., Neumann, P. & Schweiger, O. Global warming promotes biological invasion of a honey bee pest. Glob. Chang. Biol. 25, 3642–3655 (2019).

  11. Mid-Atlantic Apicultural Research & Extension Consortium. Small hive beetle. MAAREC (2015). (Accessed: 22nd September 2020)