The following is extracts from a report commissioned by the French prime minister and submitted at the end of 2008. Any peculiarities in the wording is entirely the fault of my translation. I’ve used the word*fondatrice* in French because I couldn’t think of the English equivalent. It means the egg laying female that founds a wasp colony. I hope it may be of interest to some of you.
There are 10 subspecies of vespa velutina. The one present in France is vespa velutina nigrithorax.
The interaction between hornets and bees is not well known. In Asia, apis ceranae defends itself against vespa velutina causing the hornet’s death by overheating. Apis mellifera introduced into Japan used the same behaviour, massing around the hornet and vibrating their wings,but with less success than apis cer.
VVN was first reported in France in Nov. 2004. It is believed that it was introduced around 200 by the transport of *fondatrices* on merchant ships coming from China.
The development of its installation follows the water system. Following generations firstly become denser in population in and around urban zones before colonizing the surrounding countryside.
In 2007, the number of reported identifications in the Aquitaine region was: Gironde 1260; Dordogne 1013; Lot-et-Garonne 628. In these 3 departments, damage to apiaries has been noted (estimated at 150 to 200 hives in Gironde).
Vespa velutina has a diet that varies according to available food sources. A species that develops an aggressive defence will be less bothered when an easier food source is available. This was corroborated by the observation of 2 apiaries. One, situated near to a VVN nest but in an environment rich in other prey (flies, spiders, caterpillars, etc.) was visited irregularly by the hornet. The other, in an urban setting, suffered a permanent pressure.
The rate of territorial expansion shows a rapid increase in population density. This is confirmed by the first estimations of nest density evolutions in a zone. Recorded numbering in 2006 and 2007 indicate on 2 sites an increase factor of 2.2 and 4.8 respectively. No particular limiting factor has yet been identified. No trace of illness or parasites has been found in nests that have been removed.
Impact of VVN on the apiaries.
Apiary predation, apart from killing the workers, has other effects upon a colony. According to the first observations carried out in 2007, the impact on the apiary of the predatory pressure of VVN with respect to the average number of hornets present at the hive entrance throughout the day, from July to October, can be schematized as follows:
Average presence 2 hornets in front of the hive brings on stress; the bees react. Already, at this level, egg laying is reduced, even though the impact on the population is small. Pollen and nectar harvesting slows down.
Av. 3 to 5 hornets greatly disturbs the colony and increases its reaction. Pollen and nectar harvesting is disturbed enough to risk overwintering problems. From 3 hornets per hive, honey production is non existent.
Av. more than 5, the colony is threatened in the short run. Egg laying stops, and the larvae die and rot in their cells, house bees being too preoccupied to clean. This also increases the risk of pathogen development.
Also observed is massive robbing of the weaker colonies. The hornets enter the hives and can destroy them in a few hours, taking away the honey, the bees and the larvae.
Hive protection.
Different methods have been tested to reduce the hornet’s predatory efficiency when the workers return to the hive. The idea is to reduce the space that the hornet can use during its hovering flight, or to put a screen between it and the incoming bee. In practice, these methods which restrict the *landing cone*, force the bee to reduce speed which makes it easier to catch. A screen under the hive, when it is on a stand, eliminates one of the hornet’s most effective hiding posts.
As soon as the honey is harvested, and the bees prepared for winter, the hives equipped with an entrance reducer of height 5.5mm are adequately protected (the classic arcade types are inefficient against the hornet). This protection cannot be used in season as it slows down the harvest, facilitates the capture of foragers, and prevents the passage of drones.
Trapping the *fondatrices* seems to be the most efficient way of limiting the population development. However, such an action, especially if carried out on a wide scale, could have serious consequences for the insect fauna. It is therefore necessary to to develop an extremely selective trap for VVN and have a rigorous follow up of any actions undertaken. Also, to be effective, the trapping must take place when the *fondatrices* come out of wintering. Such a trap has been designed and is actually being tested.
