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The Asian threat The Asian hornet, Vespa velutina, would not have caused any comment in Europe until a chance event in 2004, when an over-wintering queen arrived in south-west France in a consignment of garden porcelain from China.

Two questions are commonly There have been several over winter in a sheltered asked. First, what is the other instances where place protected from difference between a bee and and yellowjackets the elements. Rising air John Hill a wasp or hornet? By and have been introduced temperatures in spring cause large, bees are vegetarian accidentally into parts of the queen to awaken, usually MVB MRCVS and wasps and hornets are the world – yellowjackets in mid-April. It is difficult – if carnivores. Bees collect nectar to southern Australia, for not impossible – for her to John qualified from Trinity for carbohydrates and pollen example – usually through the re-enter hibernation, so if she College, Dublin, in 1975, and for protein; wasps and hornets inadvertent introduction of wakes up too soon she will recently retired as senior eat other insects, although an overwintering queen rather die of starvation. She starts partner in a six-vet, mixed they will find nectar or steal than the specific movement of a to feed on any nectar or tree practice in County Antrim, honey for fuel. nest, which would be deliberate. resin available as her fat Northern Ireland. He is reserves are low or exhausted. currently a trustee of the Pet Second, what is the difference Vespa velutina has very This helps to activate Blood Bank and is the founder between a wasp and a hornet? distinctive yellow legs – the her ovaries. president of the recently The general public refer to a only species in Europe to have formed British Bee Veterinary non-hairy, slim stinging legs this colour. There are It is believed – but not Association set up to raise as a wasp (whereas a bee is 12 sub-species and the one yet proven – that queens knowledge of bees within the more rounded and hairy); that has invaded France has undertake a post- profession. He also sits on the hornets tend to be bigger – a black thorax and is known hibernation migration Bee Health Advisory Forum, at least two centimetres in as V. velutina nigrothorax. and are capable of flying which advises ministers and length. There are some precise It has been mistaken for the considerable distances. politicians on bee policy, anatomical differences too , Vespa This is a feature of many and is an enthusiastic – the distance between the crabro, the wood wasp, hornet species and would go beekeeper himself. ocelli and the back of the head Uricerus gigas and the belted some way to explaining the is greater in hornets and the hoverfly,Volucella zonaria. rapid expansion of territory relationship between the ocelli in France and surrounding and the compound eyes. Life cycle countries. Accidental A queen, mated in the movement by human means Wasps and hornets belong previous season, hibernates is also a probable factor. to the family Vespinae and have 19 species in the cavity Figure 1. Asian hornet larvae in comb cells. nest group (Vespula) and 14 species in the open-air nests (Dolichovespula).

In the UK and most of Europe, there is only one species of hornet, Vespa crabro, and eight species of wasp or ‘yellowjacket’. V. crabro is often mistaken for the Asian hornet but is much bigger in 0.5 size. There has also been a hours* misidentification in the media about the Asian hornet, Vespa velutina. The newspapers published lurid articles about the Asian hornet but showed

*Suggested Personal & Professional pictures of the giant Asian Development (PPD) hornet, Vespa mandarinia. The latter is a much more aggressive species than V. velutina but, thankfully, still confined to Japan – where 20 individual INSECTS hornets can decimate a honeybee colony in 30 minutes.

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Figure 2. Hornets enlarging their nest. Figure 3. Asian hornets ‘hawking’ a bee hive.

The embryo nest At night the queen sleeps ‘queen usurpation’ and can in size (Figure 2). Each layer is During the next few weeks, on top of the nest and her result in several dead queens a series of concentric circles, the queen seeks out a nesting body heat assists the larval being found below an embryo each larger than the previous site – a wall cavity, garden and pupal development. It nest – even ‘victorious’ queens one; and every cell can be used shed or tree hollow. The nest takes her about 50 days to may be injured in these fights, up to three times to produce is secured by a petiole to the build the first 40-50 cells in so nests may fail or be smaller generations of workers. surface and is the single point which she will rear the first than usual. Queen usurpation of contact. The entrance is 10-15 brood into adult female appears to be an important As the colony grows, the located at the bottom and workers. The time it takes for control mechanism for hornet inside temperature stabilises the lower end has an initial each egg to develop into an and wasp populations. at a steady 30°C and brood comb of hexagonal cells and adult decreases as the colony development speeds up worker is surrounded by a single increases, owing to more heat. There is a brief period when development time – reducing layer of ‘paper’ resembling workers and queen work from about 50 days to 30 days. an envelope, only four to five The queen has to spend time outside the nest, but after centimetres across. away from the nest, so it is about two weeks the queen ‘Hawking’ vulnerable to attack from stays in the safety of the nest. Foraging hornets seek out The material is gathered predators, such as ants. She Her main task is egg laying; honeybees, in particular, by scraping wood with her applies a chemical repellent to whereas the foraging, brood although they will also predate mandibles from sources such the petiole; which is produced rearing and defence is carried on bumblebees, solitary as fences and telegraph poles, from a special set of glands out by the increasing numbers bees, small wasps, moths which is chewed and mixed (Van der Vetch glands) found of workers – whose body size and hoverflies. They hover (or with saliva in her mandibles inside her abdomen and is initially small but increases ‘hawk’) outside and around the to make paper. Different spread by an area of small as the colony enlarges. The entrance to a bee hive (Figure colours of paper indicate hairs forming a brush on the queen becomes the centre 3) and will pluck a honeybee different woods as the queen underside of her abdomen. of attention as the workers’ out of the air, fly to a twig and builds a new brood cell each The repellent has to be behaviour changes to serve her pull off its head, abdomen, day. Once the first few cells applied freshly each day. – licking her so she becomes wings and legs and fly the thorax are finished, she lays an egg hairless and shiny – and containing the flight muscles in each which is glued to the Usurpation aggressive workers guard the back to the nest to feed larvae. cell wall. The egg hatches Ants may be a nuisance to a entrance to the nest. after three to four days and nest but the main threat is The adult hornets are unable the larva clings to the old egg from other hornets. If a nest As the nest expands, a series to eat the bee thorax because casing to stop itself falling is destroyed accidentally, the of horizontal combs are ‘shucks’ of flesh are too big to out of the cell (Figure 1). It queen does not attempt to built and held to pre-existing pass the petiole between their goes through four moults, rebuild. Instead she will search combs by pillars. The petiole thorax and abdomen. Larvae, spins a silk cocoon, before for another nest and attempt is strengthened to take the however, do not have this moulting a fifth and final time to take it over by killing the weight and the pillars are restriction and so they eat and into a pupa. other queen. This is known as strengthened by embedding digest the meat voraciously. old cocoons into the paper, Adult requirement for protein making it as tough as concrete. is not high; but if they need Paper is taken from the inside it, they stimulate the larvae “It now seems likely, however, that it could wall of the envelope to make to regurgitate digested food appear anywhere in Britain owing to the new cells and new paper is for them. Their carbohydrate added to the outside wall, requirements are met by mass movements of goods and vehicles” such that the nest increases nectar, honeydew and tree

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to 14 days, never to return; and The Tetbury nest was a little is known of their mating surprise because the first Key behaviour. The newly mated sightings of the Asian hornet queens seek out somewhere had been expected to be First nest to hibernate until spring; and somewhere along the English the vast majority – around 99 south coast, where there is a colonised departments per cent in some estimates – system of sentinel hives in key in 2017 die during winter. As autumn areas, such as near ports and colonised departments progresses, more and more harbours. It now seems likely, before 2017 ‘sexual’ larvae are produced, however, that it could appear which are attempting to anywhere in Britain owing to without data/ probably missing mature whilst also feeding the mass movements of goods the worker population. At and vehicles. some point the demand for food outstrips supply and the Is control possible? colony fails. In a mild autumn, The National Bee Unit has this point is reached later, so a contingency plan to find more ‘sexuals’ are produced and destroy nests, but the before decline. Once all the workforce is very small and workers die, the nest will not will rely on the public to be reused – which is in contrast report suspicious sightings; to honeybee homes. so education of the public to Figure 4. Map showing the spread of the Asian hornet in Europe correctly identify the Asian since 2004. The threat begins hornet is key. There were In the winter of 2005, two 4,000 such reports in 2017, resin, especially in spring The queen starts to lay eggs hornet nests were spotted with many people mistaking and autumn. destined via parthenogenesis in the region of the European hornet and to become males. Worker France by a farmer who wood wasp for Vespa velutina. Beekeepers can take steps numbers drop from a peak of destroyed them with a to thwart ‘hawking’ hornets 1,200-1,500 and eggs destined shotgun – subsequent The nests are very difficult by draping a ‘skirt’ around to be queens are laid – the enquiries showed that three to find, especially if they are the hive stand to prevent mechanism of how a fertilised nests had been seen in that in an evergreen tree, and the hornets from hiding under the egg becomes a queen instead area in 2004. Vespa velutina Tetbury incident was a case in hive to ambush departing or of a worker is unknown. is a flying athlete and can point. The nest was 30 metres returning bees. Hornets do fly 50 kilometres. The insect up in a tree in a garden and not like any interference with Eggs destined to become has spread through France was only visible within a small their wings, so placing a wire males or queens are laid in with remarkable rapidity and angle (Figure 5). Nests are cage over the hive entrance – the larger cells at the bottom spilled into neighbouring more easily seen in deciduous with cage gaps slightly smaller combs of the nest. A mature countries, possibly assisted trees once the leaves fall, but than the wingspan – thwarts nest can have upwards by motor vehicles. by that stage the ‘sexuals’ their approach. The bees have of 12,000 cells – though will have left; so finding and a much greater volume of whether one of this size French beekeepers have destroying the nests before space to evade the hornet too could be produced in the UK reported that their honey ‘sexuals’ appear is vital. and their coming and going is remains a debatable point. production is down by two not impeded. The males and queens lay thirds since the Asian hornet Defra is trialling the use of down fat deposits in their arrived. This situation is highly sophisticated drones The hornets usually outgrow abdomens by eliciting sugars unlikely to improve because with very sensitive heat-seeking this initial nest and so the from the larvae; whereas the the density of nests will cameras in an effort to find queen will initiate work workers do not lay down fat increase in those areas mature nests – and possibly on a secondary nest at a deposits because they will already affected. The hornet embryo nests too. Professional much higher level above the not be living long. has now spread into Belgium, teams are required to destroy ground. They do not swarm the Netherlands, Germany, nests because they will have as honeybees do. A favoured The numbers of males and Italy, northern Spain, proper clothing and machinery position is found and within queens produced depends on Portugal, Majorca and the to reach high into trees. a few days a nest the size of the weather. On average there Channel Islands (Figure 4). a football can be produced – are 300 queens and 600 males; It has been found in Britain The hornets are very defensive some nests in the Far East have but in an ‘Indian summer’ these on at least two occasions once they sense their nest is reached a metre in diameter. figures can rise to 1,800 queens – firstly in Tetbury, near threatened, and several people The queen will be in full lay in and 1,800 males. They remain Bristol, in September 2016, have died in France as the this new nest, producing up to in the nest for a period of time; and then in Woolacombe, result of being stung whilst 100 eggs a day. although the original queen Devon in 2017. A desiccated trying to remove nests. It is often disappears at this point. specimen was also found in believed that ‘guard’ hornets Reproductive phase Dorset and a single hornet will sound a warning and, In late summer/autumn, the The males leave first at eight to caught flying in a Tesco if not heeded, will return to reproductive phase begins. 11 days and the queens at 13 warehouse in Scotland. the nest to recruit a more

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by the time the nematode Future prospects population rose to have an It seems inevitable that V. effect, it was too far into velutina will invade the British the nest cycle to prevent Isles at some point and our the ‘sexuals’ developing. initial response must be to Unfortunately, these eradicate it as we have done so parasites have little overall far. There is a contingency plan effect on a resilient hornet and this will require education either, and any control would of beekeepers and the public. need to kill the queen early in The lesson from France is the season. that, once established, this species is almost impossible One species that does have a to eliminate. There may come ‘strategy’ is . This a point when we may have to bee has evolved with hornets consider that possibility. over a very long time and it has a behavioural skill. When Varroa mite has made an Asian hornet or giant beekeeping much more hornet comes too close to the difficult and has placed a Figure 5. The Asian hornet nest high in a tree in Tetbury. hive entrance, it will sound a huge pathogenic burden on warning ‘fizzing’ sound and the honeybee. The Asian substantial force. It has also (Vespa dybowskii) which takes perform a ‘Mexican wave’. hornet is another unwanted been reported that, under over colonies of wasps and pressure with which it will have extreme threat, worker hornets European hornets. However, If the hornet lands, hundreds to contend; plus the threat will curve their abdomens its effect on the hornet of bees will engulf it and posed by the small hive beetle under their bodies and ‘spit’ population is minimal and the attempt suffocation, while at spreading from southern Italy venom at the assailant in an drawback is that it is a very the same time vibrating their into other parts of Europe. effort to blind them. aggressive insect. wing muscles to generate heat. Apis cerana can survive It has been suggested that Is there any biological Hornets can become heat up to 45°C; whereas the the climate in Britain is such system of control? infected by a variety of hornet is cooked and dies at a that the Asian hornet could Pitcher plants are carnivorous highly specialist parasites – few degrees lower. only survive in the southern plants that seem to attract about 20 species are known parts of England, Wales and Asian hornets in France, although little is known Western honeybees do not Ireland, or below 55 degrees so research is in progress of their pathophysiology. exhibit this behaviour and latitude because temperatures to identify the attractant, These include Stylopids, are, therefore, vulnerable to above this location would be in the hope of producing a nematode worms, moths, attack. It is an unfortunate too cold for it to survive. On commercial product that beetles,Trigonalid wasps, fact that between 30,000 to the other hand, some experts would attract the hornets ichneumon flies and some true 60,000 honeybee colonies are suggest that it will go right into a trap. Traps of various flies. The number of colonies destroyed in Japan every year to the north of Scotland – its design are in use but have infected is small and so the as a consequence of hornet presence in the mountainous the disadvantage of trapping overall effect is minimal. attack. That amounts to 10 areas of northern Spain may ‘good’ pollinators as well. to 20 per cent of Japanese lend some credence to this. Japan has the honey buzzard Mermithid nematodes colonies. It is also worrying (Pernis apivorous) which has infect both wasp and hornet that Vespas velutina is The hornet has spread rapidly feathered feet to prevent colonies. New Zealand becoming adapted to urban through much of Europe being stung; and hornets are used them by releasing environments in Japan, owing and the number of nests eaten by humans as a delicacy large numbers into the to the abundance of food per geographical area will – being caught by specialist environment in an attempt to in towns and cities, and this inevitably increase. There is hunters. Some parts of Asia control yellow jacket wasps. will bring them into closer little good news here. have a parasitic cuckoo hornet It did not work; because contact with humans.

References

Davis I and Cullum-Kenyon (2012). BBKA Guide to Beekeeping.

Graham JM (2010) The Hive and the Honeybee.

Martin SJ (2017). The Asian Hornet (Vespa velutina) Threats, Biology and Expansion. University of Salford.

Root Company (2009). The ABC & XYZ of Bee Culture.

Sammataro D and Yoder JA (2012). Honey Bee Colony Health. CRC Press.

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