The Asian Hornet (Vespa velutina) is one of many imported pests which plague European beekeepers. It landed in France early 2004 after a single queen caught a ride on pottery from China, from this lone queen the hornet has expanded across seventy percent of the country. Following rivers, it has migrated north into Belgium and Germany. Recently its southern migration has been confirmed with the hornet being found in Spain, Portugal and Italy.
Although smaller than our own European hornet the Asian’s hunting method of catching foraging bees returning to the hive can weaken the hive far more significantly that the odd foraging bee a European hornet may catch in the field.
There is also a risk to humans as the hornets build large nests, up to one meter in diameter, and are highly aggressive. This has led to many parts of the tabloid press inevitably labeling them ‘killer hornets’. The media often mistakenly printing pictures of the World’s largest hornet, the giant Asian hornet, alongside these articles. – I guess they look scarier.
Asian Hornet courtesy of http://www.nationalbeeunit.com : Giant Asian Hornet courtesy https://www.flickr.com/photos/justinlindsay/
As an English beek I know it is inevitable that these will one day make their way across the channel and become another problem I’ll have to deal with. However, research recently published demonstrates the impact of a lack of genetic diversity within the Asian hornet population – who all share the same mother from the original French landing in 2004.
The life cycle of a hornet colony can be split into two phases: growth and reproduction. From spring to the middle of autumn the hornet concentrate on building the colony producing predominantly workers. From autumn the colony starts to raise queens and male drones. Unlike honey bees the original queen dies in the colony at the end of the season but the young mated queens hibernate over winter then go on to establish new colonies in the spring. This research found two things:
- That Asian hornet colonies in Europe are raising male hornets far earlier that they are normally expected to do in their native habitat. Like honey bee drones, males do not contribute to the growth of the colony. The consequence of this is that the colony is expending resources unnecessarily creating males; this can limit colony development.
- It was also found that the males produced early in the season where diploid (for a primer on bee genetics go here) meaning they have a two sets of chromosome rather than the normal single set. Diploid drones are a common problem in heavily inbreed honey bee populations but are rare in wild populations with normal genetic diversity. Diploid drones are less productive in terms of reproductive performance. They have such a negative effect on colony performance that within honey bee colonies the workers will destroy any diploid drones they discover.
This phenomenon is well known as inbreeding depression in which a population which breeds extensively with its direct relatives becomes weakened and less competitive. One of the more famous examples of this in Britain is the plight of the moss carder bumblebee. In 2000 a study carried out at the University of Stirling demonstrated that the isolated populations of these bees lead to infertile males.
The Asian hornet will continue to be a challenge to beekeepers across Europe and undoubtedly at some point British beeks as well.
However, it nice to know they have their own problems as well.