Beekeepers in north Queensland have been familiar with Apis cerana, the Asian hive bee, since it was discovered in Cairns in 2007. There are now concerns that Varroa destructor (Varroa) will be able to switch back and forth between A. cerana and A. mellifera (the Western honey bee, often referred to as the European honey bee). If this is the case then A. cerana may drive high mite loads in managed A. mellifera colonies, as the Varroa population has more hosts on which to reproduce and any colonies that break down with high mite loads will become ‘mite bombs’, spreading Varroa to surrounding colonies of both species.
However, there are several points to keep in mind:
- Varroa typically only reproduces on drone brood of A. cerana – Varroa reproduction is limited to when there is drone brood being reared, and the amount of drone brood is less than the amount of worker brood
- Varroa does not tend to lead to the breakdown of A. cerana – they will not be a source of mite bombs
Evidence for and against host switches
Research assessing the ability of mites to reproduce when swapped between species has been mixed (Grindrod & Martin 2023). In some instances, Varroa has been infertile when switched to a different host species. However, only two studies used mites from both A. mellifera and A. cerana. Further, mites are often collected for transfer from worker brood cells. Since Varroa does not reproduce on worker brood of A. cerana this could bias the results.
Genetic testing can shed further light on the subject. If Varroa on both species in the same area are from the same genetic lineage this indicates that Varroa is likely able to switch between the hosts; if the lineages have diverged this indicates that host switches are unlikely – if the populations are genetically distinct then Varroa is not switching between them and mixing genes between populations. Beaurepaire et al (2015) performed genetic testing on Varroa sampled from A. cerana and A. mellifera from the same or adjacent apiaries in the Philippines and Vietnam, their results suggest the following:
- Varroa can switch hosts in the Philippines
- Varroa cannot switch hosts in Vietnam
- There may be more Varroa species than thought
Conclusion
There is a lack of reputable data about host-switching between A. mellifera and A. cerana. However, it is possible. Whether it is possible in northern Queensland will likely depend on the strain of Varroa present in Australia, and possibly on the strain of A. cerana. The impact on beekeepers if Varroa can switch between hosts is likely to be greater if A. cerana is producing large amounts of drone brood.
Acknowledgements
- Asian Honey Bee Literature Review 2013
- Grindrod & Martin (2023) Varroa resistance in Apis cerana: a review. Apidologie 54:14
- Beaurepaire, Truong, Fajardo, Dinh, Cervancia & Moritz (2015) Host specificity in the honeybee parasitic mite, Varroa spp. in Apis mellifera and Apis cerana. PLoS One 10: e0135103
- Image – Apis cerana, courtesy Nadine Chapman
- This article was peer-reviewed by Madeleine Beekman and Ben Oldroyd.
