Pathway 1: Cross-Channel flight
The shortest distance between England and France over the English Channel is 34 km, between Dover and Cap Gris Nez. Vespa velutina is present in at least one coastal area of France (Figure 6) (Northern Brittany since 2008; Côtes d’Armor since 2010). In the highly likely event that V velutina increases its European range and also spreads to other more northerly coastal regions of France, then in theory inseminated hornet queens could fly across the Channel. Distances covered by adult V velutina in single flights are unknown but unpublished data on V velutina’s flight capacity in the laboratory suggests that they can fly dozens of kilometres in one flight, with certain weather conditions (wind direction) assisting natural spread. There are no confirmed records of other social Hymenoptera crossing from continental Europe to the UK via this pathway, but the Median wasp, a non-native species established in the UK since 1980, was first recorded in the coastal area of East Sussex, implying that it flew here across the Channel. There are numerous records of other insects, including species far less sturdy than hornets (butterflies, ladybirds, etc.) making this journey each year, sometimes in vast numbers. This entry route is thus considered relatively likely for V velutina.
Pathway 2: Hibernating queens in wood/ wood products
Asian hornet queens like to hibernate under bark and will cluster in small groups to overwinter. Vespa velutina’s preferences for particular tree types are unrecorded, so it is impossible to be specific about the likelihood that they will associate with any given species. However, every year we import a huge volume and a wide variety of wood and wood products from countries where Asian hornets are known to be present, both within its native Asian range and from within the EU. Import regulations and potential detection measures depend on tree species, country of origin and nature of wood product. These are summarised in the Forestry Commission Plant Health Guide Importing wood, wood products and bark (Forestry Commission, 2007) and also Plant Health Directorate 2000/29/EC. Regarding wood and wood products imported from outside the EU, the fact that controlled commodities lack bark and/or must be treated prior to entry greatly reduces the probability that V velutina will survive existing management practices. However, most wood entering from the EU is subject to fewer controls.
Inseminated V velutina queens do not only hibernate in ‘natural’ nooks and crannies; they will also use man-made sites as long as these provide small, well-insulated refuges in which they can hide away over the winter months. The range of imported commodities that offers suitable hibernation sites is thus extremely broad and impossible to measure or control. It is believed that V velutina was imported into France from Yunnan (China) in ceramic bonsai pots. Ceramic garden goods from France, Spain or elsewhere in mainland Europe can be imported into the UK without any inspection that would reveal hibernating hornets and, like France, we also import bonsai pots from Asia. ã [This article will be concluded next month.]