Vespa velutina Lepeletier, 1836

The Asian predatory wasp, also known as the Asian Hornet or yellow-legged hornet, (Vespa velutina) is a species of hornet indigenous to Southeast Asia. It is of concern as an invasive pest species in some other countries.^[1]

Appearance[edit]

Vespa velutina is slightly smaller than the European hornet. Typically queens are 30 mm in length, and males about 24 mm. Workers measure about 20 mm in length.^[2] The species has distinctive yellow tarsi. The thorax is a velvety brown or black with a brown abdomen. Each abdominal segment has a narrow posterior yellow border, except for the fourth segment, which is orange. The head is black and the face yellow. Regional forms however, vary sufficiently in colour to cause difficulties in classification, and several subspecies have been variously identified or rejected. The form Vespa velutina nigrithorax is the one that is causing concern about its invasiveness in Europe.

Biology[edit]

Like other hornets, Vespa velutina build nests that may house colonies of several thousand individuals.^[3] Females in the colony are armed with formidable stingers with which they kill their prey and defend their nests. The nest is of paper, roughly in the shape of a prolate spheroid with a vertical long axis. It commonly grows very large, more than half a metre in length. Unlike the nest of the European hornet, Vespa crabro, its exit is usually lateral rather than at the bottom. The nesting season is long, and a colony commonly begins by building a nest in a low shrub, then abandoning it after some months and rapidly building a new one high in a tree, possibly as an anti-parasitic measure. The next generation of young queens finally will disperse for the winter.^[4]

Vespa velutina opportunistically hunts a very wide range of insects, including flies, dragonflies and Orthoptera, typically capturing them by pursuit.^[2] The major concern about their invasiveness however, is that when they find a bee colony or an apiary, they tend to settle down and specialise in honeybees as their prey. A wasp occupies a position above a beehive as its hunting territory. It flies about within an area of about half a square metre, scanning the direction from which foraging bees return to the hive. Each wasp vigorously defends its hunting territory, chasing off any rivals. However, as soon as it catches a bee it flies off and another wasp replaces it, usually within a few seconds. The circadian activities of the two species of honeybees are similar, and the hunting wasps match them; their most intense activity is in the morning and afternoon, not near dusk or noon.^[1]

In their native range Vespa velutina mainly hunt Apis cerana, the Eastern honey bee, which has evolved a strategy of avoiding hovering hornets by rapid entry and exit from the hive when hornets are about. The guard bees also ball hornets to death. However, where the European honey bee has been imported, Vespa velutina finds them easier prey than Apis cerana because Apis mellifera have not been subjected to selection for countering concentrated hawking by hornets. For example, Apis mellifera approach their hives more indirectly and slowly when they detect hawking hornets, instead of darting in as fast as possible in the way that Apis cerana does. They also ball hornets to death in the way that Apis cerana do, but less effectively, and they do not achieve as high a temperature in the ball. Furthermore, when they detect that wasps are hawking, Apis cerana tend to withdraw into the nest and Apis mellifera do not.^[1]

Apis cerana guard bees also use wing shimmering in response to the presence of Vespa velutina. This is a very generalised response to disturbance and has variously been suggested to be an aposematic signal or a strategy for disruption of visual patterns, similar to the behaviour of Apis nuluensis and Apis dorsata.^[5]Apis mellifera exhibits no such behaviour. In any event, when Apis mellifera occur together with Apis cerana. Vespa velutina preferentially hawk Apis mellifera foragers.^[1]

Distribution[edit]

Vespa velutina originates from Southeast Asia, particularly the tropical regions, from Northern India, Pakistan, Afghanistan, Bhutan, China, Taiwan, Burma, Thailand, Laos, Vietnam, Malaysia, the Indo-Chinese peninsula and surrounding archipelagoes.

As an invader the wasp has appeared in France, Spain, Portugal, South Korea and Japan. Further invasions are expected in various countries including much of Europe.^[6]

Pest status and invasiveness[edit]

Vespa velutina has become an invasive species in France where it is believed to have arrived in boxes of pottery from China in 2004.^[7] Since then the wasp has been preying on honeybees. Humans have been attacked after disturbing hornets; although the species is not aggressive it "charges in a group as soon as it feels its nest is threatened".^[3] There have been reports of people hospitalised in France after suffering anaphylactic shock as a result of multiple stings. Because of hornets' larger size, their sting is more serious than that of a bee.^[7]

By 2009 it was thought there were several thousand nests in the area of Bordeaux (capital of the Aquitaine region) and surrounding départements.

The wasp has spread to northern Spain, as confirmed by the Beekeepers Association of the Basque Country (Gipuzkoako Erlezainen Elkartea) and the Neiker etimology institute in Irún, after breeding colonies were found.^[8] It has reached Portugal in 2011.^[9]　Also reported as naturalised for the last 3 years or so on the Japanese island of Tsushima.^[10]

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  Vespa velutina - usual colour variant. Dorsal aspect.

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  Vespa velutina - usual colour variant. Lateral aspect.

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  Vespa velutina nigrithorax, dark colour variant - Toulouse.

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  Nest of Asian predatory wasp approximately 30 feet up on a durian tree in Malaysia.

References[edit]