Patterns of food transfer in yellow-legged hornet nests revealed by heavy metal tracers
A social insect colony can be seen as a superorganism in which nutrient collection and regulation is achieved through the collective action of workers. Here we investigated how workers of the yellow-legged hornet Vespa velutina, an invasive predator of honeybees and other insects in Europe, distribute the incoming food within their nests. Food transfer among colonies differing in composition of developmental stage and abundance of different castes was compared by feeding workers with protein and carbohydrate solutions labelled with non-radioactive heavy metals (rubidium and caesium) and measuring the heavy metal tracers' occurrence in adults and larvae in the nests after 24h. Caesium labelled sucrose was more abundant in the adults (workers, males and the queen), while rubidium labelled proteins were more abundant in the larvae. The lightest larvae received more protein than the others. The lightest workers received more carbohydrate, and the largest workers more protein. Even if this work is exploratory, our results considerably improve our knowledge of hornet biology by showing how food distribution patterns may vary throughout the development cycle of colonies. They also provide new perspectives to understand how specific nutrients are distributed in nests, and may help develop Trojan horses biological control strategies based on food distribution.