A Foreigner in France: the Asian Hornet in 2004 the Hornet Vespa Velutina L
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A foreigner in France: the Asian hornet In 2004 the hornet Vespa velutina L. was accidentally introduced into the South West region of France, probably via garden pots imported from China. Eradication of the species from France is now impossible. As this hornet is a predator of honey bees, the introduction into Europe of V. velutina is certainly bad news for beekeepers. Marie-Pierre ince its first introduction to France and central China, as far east as Taiwan Chauzat1 and in 2004, Vespa velutina has spread and as far south as Indonesia (Archer, Stephen Martin2 Sto 24 ‘départements’ from the 1994). When V. velutina occurs in tropical Charente-Maritime to the Gard (Haxaire regions, nests are normally found in the 1Food Safety et al, 2006) (Figure 1). Its introduction cooler highland or upland regions that Agency, France, was first officially noticed in 2005 in Lot- have a climate comparable to that found and 2University of et-Garonne. However field information in Southern Europe (Starr, 1992). Sheffield, UK has reported that some ‘black hornets’ The sub-species of V. velutina intro- have been observed in the vicinity of a or- duced into France is V. velutina nigritho- namental plant seller since 2004. rax (Haxaire et al, 2006), which is very The hornet has adapted well to its new easy to recognise since it is the only hor- environment, colonising urban, sub-ur- net or wasp that has an entirely dark Title image: An adult ban, agricultural and wooded areas. The brown body with only one orange band to- th hornet. Picture: Jean native range of V. velutina extends from wards the end of the abdomen (4 tergite). Haxaire. north-eastern India, throughout southern The nigrithorax colour form occurs in the 86 Biologist | Volume 56 Number 2, May 2009 Hornets | IOB Figure 1: French departments infested with V. velutina in 2009. India-China part of its distribution. The The hawking area in front of the hives life cycle of V. velutina is similar to that is territorial as other hornets that intrude of other hornets except that this species are quickly expelled. In Yunnan Province in its native range can produce very large China, hornet predation levels are highest colonies that can reach 75cm in length in the morning and afternoon, which cor- and contain up to 12,000 brood cells in 11 responds with the daily rhythm of honey combs (Martin, 1995). It has a long nesting bee flights (Tan et al, 2005). If a honey period that lasts from May to November. bee colony becomes sufficiently deprived The hornets (Vespa) consist of 23 spe- of workers, V. velutina will then enter the cies worldwide, and are widely distributed hive, feed on the honey and remove the throughout Asia. Europe has two native brood. hornet species: the European hornet, V. crabro L., which is found throughout Eu- Life history of V. velutina colonies rope and the oriental hornet, V. orienta- In France, data on the biology on V. ve- lis L., which has a distribution restricted lutina is still lacking although, like all to Bulgaria, Greece and Southern Italy. hornets and wasps, their nests are made Both species produce much smaller colo- of paper and mature nests are typically nies than V. velutina and are much less built near the top of trees or on buildings aggressive despite both being larger than – although subterranean nests have been V. velutina. recorded (Martin, 1995). The following in- In Asia, V. velutina is a predator that formation is based on direct observation Figure 2. V. velutina often focuses on European honey bees from Asian V. velutina colonies and is sup- attacks honey bee foragers when they return (Apis mellifera L) and to a lesser extent plemented by information on V. simillima, to the hive. the Asian honey bee (Apis cerana Fab.). In a hornet with a very similar biology. Picture: J. Haxaire India (Kashmir), V. velutina has been re- ported to limit colony development of Eu- ropean honey bees by the persistent pre- dation of adult bees (Shah et al, 1991). V. velutina is one of the most adept hornets at catching honey bees on the wing: other species land on the hive and grab indi- viduals that try and attack the hornet. V. velutina workers hover in front of the hive waiting for returning foragers (Figure 2). When the unsuspecting honey bee nears the hive the hornet swoops down, catching its victim on the wing. The head and ab- domen are removed and a meatball made of the flight muscle which is fed to larvae back in its nest. Volume 56 Number 2, May 2009 | Biologist 87 IOB | Hornets queens are produced: there is a good cor- relation between the number of queens produced and colony size, so larger nests produce more queens. If the queen dies be- fore sexual production, some of the work- ers will develop their ovaries within a few days and lay unfertilised (haploid) eggs. These will develop into males, and can mate with new queens if present. Queen- less V. velutina nests have been reported in France. All nests are only ever used once and are destroyed by birds or the weather, although the same nest-sites can be used year after year. A key characteristic of hornets such as V. velutina is their resilience to environ- mental change and their capacity to over- Figure 3: Embryo nest of V. velutina observed in France in a protected area. Picture: J.Haxaire come difficulties. Hornet populations com- monly fluctuate between years, often with a two year cycle that may be superim- All hornets have an annual lifecycle, posed on longer fluctuations. For example, with the mated queens emerging from population studies on the common wasps their over-wintering hibernation period Vespula germanica and Vespula vulgaris in spring. The queens quickly establish a in the UK found a two year cycle possibly small embryo nest, usually in an enclosed enclosed within a longer seven year cycle and protected place, such as a wall cavity (Archer, 1985). It remains unknown what or tree hollow. In the tennis ball-sized em- drives these population cycles; limited bryo nest, the queen rears her first batch nest sites and usurpation (queen fighting) of workers. rates have been suggested (Martin, 1992) In V. simillima these embryo colonies and the summer and autumn weather cer- often undergo relocation when 50-100 tainly play a role, but large fluctuations in workers are present (Dazhi et al, 1989), nest numbers between years are a trait since many sites do not allow for rapid common to all hornets. It is also unknown nest expansion, so forcing the colony to re- whether V. velutina populations in France locate to a new less constricting site, such will follow this trend but it seems unlikely as high in a tree (Figure 3). After reloca- in an expanding population where nest- tion the nest expands rapidly as increas- sites will not be limited. ing numbers of workers help to rear more workers with the queen being restricted to Thermoregulation egg-laying within the nest. In the autumn One of the key factors that allows hornets the colony reaches it maximum size con- to be highly successful predators is their taining over 1,000 adult workers and hun- ability to thermoregulate their nests. The dreds to thousands of ‘sexuals’, i.e. new horizontal combs that contain the brood queens and males. The new queens and are enclosed within a nest envelope that males mate outside the colony, the males protects the adults and brood from both and workers die with the onset of winter high and low ambient temperatures by due to the lack of food, while the mated preventing heat loss from the nest interior queens enter hibernation. Queens hiber- (Figures 4 and 5). As the size of the colony nate alone or in groups of two or three, un- increases, the ability of workers to main- der the bark of trees or stones. During the tain a stable nest temperature increases, over-wintering period queen mortality is until they are able to maintain a constant high (>99%) (Archer, 1984) otherwise the nest temperature at around 30°C, despite population would explode since hundreds ambient temperatures that may be up to and sometimes thousands of new queens 20°C lower (Martin, 1990). are produced by each colony. The high nest temperature allows hor- The climate can affect colony develop- nets to forage early in the morning when ment: in France, the mild winter of 2006 ambient temperatures are low and many allowed the continuing development of insects are immobile. It also allows them nests until late November, whereas the to mount an effective attack if the nest is wet and cold spring of 2008 noticeably de- disturbed even during cold weather or at layed the process. The longer the colony night when they are attracted to lights. survives into the autumn, then the more Despite this ability to maintain a stable 88 Biologist | Volume 56 Number 2, May 2009 Hornets | IOB Figure 4 (left). Mature nest of V. velutina scanned with X rays. Picture: Eric Darrouzet Figure 5 (right). Structure of a hornet mature nest. Picture: Stephen Martin nest temperature hornet larvae (unlike species has a unique recruitment behav- honey bee larvae) are able to tolerate a iour when intruders get too close to the wide range of temperatures. colony: a worker will ‘warn’ the intruder Hornets and wasps feed almost exclu- by flying around him. If the intruder con- sively on animal prey which they cannot tinues towards the nest then the hornet digest directly due to their narrow waist.