Asian giant hornets: why do they pose a threat and what can be done about it?

13 May 2020

Alongside the COVID-19 pandemic, media reports in recent weeks have covered another health threat affecting parts of the USA: an invasion of Asian giant hornets.

We asked our entomologists to explain how the “invasion” poses a threat and why the study of such insects is important to safeguard biodiversity, the economy and human health?

The Asian giant hornet, Vespa mandarinia, was first recorded in North America in September 2019 after sightings in British Columbia¹. The first appearance was at the port city of Nanaimo on Vancouver Island but it has not been confirmed as the point of entry.

Hornets may have arrived unintentionally through international trade. Vespa mandarinia is native to the tropical forests of Asia but can be found in Eastern Russia. In December 2019 the Washington State Department of Agriculture (WSDA) recorded them in its territory and now the WDSA and Washington State University are mounting a large scale ‘hunt’ for the species².

It is important to note that this species, Vespa mandarinia, is distinct from the invasive Asian hornet found across Europe, Vespa velutina and the European hornet Vespa crabro.

As with all bees and wasps Vespa mandarinia will only sting when threatened, and while painful, a single hornet sting is not sufficient to kill an adult human, you would be in trouble with anything over ten so it still poses a risk to human health: standard bee keeper suits offer limited protection due to the length of the sting.

As a predator Vespa mandarinia hunts a range of other insects (including mantises and other Vespa species, it specialises in other social insect nests and can decapitate other bees and wasps in ‘slaughter’ raids). In its native range Vespa mandarinia attacks Asian honey bees (Apis cerana) which have adapted by ‘bundling’ hornet scouts in swarms and shivering attackers to death with heat, a kind of death hug.

Economic

More problematic is that the Western honey bees (Apis mellifera) widely cultivated in the USA and beyond is not well adapted to Vespa mandarinia. This is the key concern of agriculturalists in the USA because Apis mellifera provides vital pollination services and revenue for honey farmers. Economic costs of the hornet have the potential to be huge, fruit pollination would likely suffer as would honey production. In 2013 the US honey crop alone was valued at $317 million³, making effective control of predators and diseases an important priority. Honey pollination services are valued at over $10 billion a year when it comes to crop production⁴.

Invasive hornets are generally bad news for native biodiversity, especially for wild bees, but these nests tend to be thinly spread in the landscape and less at risk. Recent media interest has developed due to the expected emergence of hornet Queens from overwinter inactivity, underground nests are established around late-April.

But how to get rid of this pest? Kill the Queens, these are the dispersers. Trapping and killing of Queens in Spring is a key element of control. In Japan control largely consists of locating and destroying nests in autumn, bait traps or mass poisoning of hornets using pesticides at honey bee colonies and using protective screens on hives. Early detection, trapping of Queens in spring and eradication are thought to be the most effective means of control in the US.

The USDA pest report⁵ is recommended as the most scientifically accurate and objective source of information on this pest.

In order to try and monitor the presence of the Asian Hornet (Vespa velutina) occurrences around the UK, many organizations such as BBKA, are recommending the placing of monitoring traps in Apiaries across the whole Country, even in those areas where there has been no Vespa velutina sightings. The use of traps has triggered much debate in the appropriateness in the management to identify, control and eradicate invasive species, and those species (wasps and European Hornets), that are often considered as pests.

Biodiversity

One key area that is often raised by monitoring for Vespa velutina is the importance to reduce the amount of by-catch in the trap so as not to impact and reduce the biodiversity of other insects and pollinators innocently captured. This is a key consideration when setting up monitoring at an Apiary. For example, you can select either one of two monitoring regimes, one that will kill prey, and one that will capture prey. There is more physical time involved in those traps that capture prey, as the by-catch needs to be released as soon as possible so that all non-target species can be released alive. Controversially, this may also include the release of European Hornets (Vespa crabro), as well as wasps, should you wish to do so. Although these species in themselves are often seen as pests and are routinely euthanised by many bee keepers.

Here at Harper Adams University our MSc courses in Entomology and Integrated Pest Management prepare students for careers that enable them to work as bee inspectors, applied entomologists, plant health advisors and biological control specialists. These specialists protect our native ecosystems and ensure that crop protection and food production can be conducted sustainably and with as little environmental damage as possible.