Since its introduction in France 10 years ago, the yellow-legged hornet, Vespa velutina, has rapidly spread to neighbouring countries (Spain, Portugal, Belgium, Italy and Germany). It showed efficient social traits facilitating its invasive success. Only scarce and incomplete natural history studies were known from its native distribution area. Studying the biology of this species in its invasive distribution range was thus a prerequisite to the implementation of efficient control methods in a near future. During a 3-year field survey, we collected 77 nests to investigate several of the species' key colony characteristics. Our results enabled us to accurately quantify each of the castes and to better understand their synchronicity throughout the season. Our study showed that mature nests are able to produce up to 13 000 individuals and that the size of mature nests is correlated to the number of individuals produced. This correlation enables the inference of one characteristic from the other. Furthermore, each mature nest can produce up to several hundreds of potential founder queens, a crucial datum in the light of today's unregulated spring queen trapping control campaigns. In addition, nest dissections enabled to record the incidence of nest relocation for the first time in this species. Results are discussed with regards to what is known in other Vespidae species, with a focus on Vespula species that are known to be invasive in many other countries worldwide.

Summary The invasive yellow‐legged hornet was first discovered in Europe, in south‐western France, in 2004. It has since spread very rapidly and has caused significant mortality among honeybees and native entomofauna. It also poses a risk to humans because its sting provokes allergic reactions. The objectives of this study were the following: (i) to disentangle the roles played by human‐mediated dispersal and self‐mediated dispersal in the species' rapid range expansion and (ii) to estimate the intensity of control measures in France and determine what needs to be done to slow the hornet's spread and dramatically reduce its population densities. A mathematical model was developed to describe the hornet's potential spread. This model included parameters describing the population growth rate, carrying capacity, self‐mediated dispersal, human‐mediated dispersal and the efficacy of control measures (i.e. the destruction of detected nests). Model parameters were estimated using 2004–2009 occurrence data for France and the model was then validated using 2013 occurrence data. Several scenarios were tested: human‐mediated dispersal was present or absent and control intensity varied. Then, the species' spread in coming years was simulated (from 2013 to 2020). Despite some uncertainty on the value of the parameters, this model is relatively robust. Human‐mediated dispersal may not be necessarily responsible for the hornet's rapid range expansion; the species could spread rapidly on its own. It is likely that to date, an average of 30–40% of detected nests have been destroyed each year. Increasing the percentage of destroyed nests from 30 to 60% could reduce the species' spread by 17% and its nest density by 29%. If 95% of nests are destroyed, the species' spread and nest density could decline by 43% and 53%, respectively. Synthesis and applications. The mathematical model developed in this study shows that human‐mediated dispersal of the invasive yellow‐legged hornet may not be the only factor explaining the hornet's rapid range expansion and that controlling this invasive pest is still possible. Therefore, there is an urgent need to reduce self‐mediated dispersal and to intensify and improve control measures to diminish the species' impact and prevent its further spread. Control measures could combine the mechanical removal and destruction of individuals or infested materials with biological control techniques.

Summary1. Models developed to predict behavioural and life-history decisions of parasitoids rely heavily on assumptions concerning the nature and function of the nutrients that the female obtains from the host. 2. Using a combination of colorimetric and thin-layer chromatography techniques, we analysed the composition of the host-feeding fluid consumed by the parasitoid Eupelmus vuilletti and found it to be consistent with the composition of the host's haemolymph. 3. The analysis of the haemolymph revealed that it was rich in proteins but also rich in sugars, trehalose and sucrose in particular. 4. Injections of these sugars at haemolymph concentrations directly into the parasitoid's haemolymph showed that these sugars are solely responsible for the increased longevity observed in host-fed females. 5. This study is the first to identify the constituents of host-feeding meals and their impact on parasitoid longevity and provide further evidence of the extent to which parasitoid behavioural decisions are determined by physiological variables. Our study demonstrates that the integration of nutritional physiology, behaviour, life history and population dynamics is essential in order to understand parasitoid foraging ecology.