Since its introduction to Europe in 2004 in the Lot-et-Garonne department of France, the invasion of Vespa velutina has proven remarkably successful, with a single fertilized female initiating the continent-wide expansion. The phenomenon is largely attributed to the facilitation of globalized intercontinental trade, enabling the entry of alien species into new areas where they establish themselves unhindered due to the absence of natural predators.
The invasion’s progression in France demonstrates an alarming speed of approximately 78 km per year. Early detection of the first nests in affected areas is crucial for effective control measures to eradicate or slow down the invasion.
The key to Vespa velutina’s successful expansion lies in the complexity of its colonies. These eusocial insects exhibit a remarkable capacity to adapt to their environment and display more aggressive and daring behavior compared to the European hornet Vespa crabro. Constructing nests from cellulose pulp in cavities and trees, these dynamic colonies undergo an annual cycle. The fertilized female initiates activity in spring when minimum temperatures exceed 10ºC or when the average temperature surpasses 12ºC. Creating a primary nest, she establishes the colony by laying diploid eggs of worker females. As the colony expands, secondary nests may be formed in improved locations or at the same site to increase nesting capacity.
At its peak development, colonies typically comprise around 6,000 individuals, though some instances describe colonies exceeding 13,000 hornets. This population surge occurs during summer, the season when they commence preying on bee colonies.
Worker hornets handle various tasks within the colony, including feeding the brood, maintaining nest temperature between 30ºC and 32ºC, and communicating food sources. The colony’s evolution is influenced by seasonal temperatures and food availability, leading to prolonged nest activity in warm areas with short winters.
Unlike other eusocial insects, Vespa velutina does not accumulate reserves for times of scarcity, necessitating a constant supply of food as the colony grows throughout the year. In fall, the colony matures, and the queen lays eggs for future breeding individuals, including haploid, unfertilized eggs that develop into males. Each nest can produce approximately 350 founding females and 900 males.
Despite high inbreeding in Europe, numerous diploid males (sterile) have been observed, yet this does not seem to impede their expansive capabilities across the continent. Vespa velutina poses a significant threat to honey bees, displaying a particular attraction to the scents of beehives. Predatory actions involve hovering in front of hive entrances, capturing returning foragers, and subsequently dismembering them. Predation is more pronounced in hives with lower defensive characteristics, resulting in severe losses and a reduction in bee foraging. Hives consistently attacked by Vespa velutina experience a winter death rate of up to 55%.
Efforts to combat this predatory species have primarily relied on the use of baited traps, often employing commercial or homemade concoctions with fruit juices, wine, or beer. However, this approach has proven inefficient, capturing only a small percentage (1-3%) of Vespa velutina, while unintentionally affecting other insect species. To enhance specificity, trapping should utilize selective traps and attractants, targeting founding queens in spring or reproductive individuals in late autumn. Poisoned baits should be avoided to prevent harm to other scavengers. Active nest control requires monitoring, triangulation, or the use of thermal video cameras for detection and specialized personnel for controlled destruction.
