Larval gregariousness in the Chrysomelidae

Abstract

Many species of leaf-feeding insects (for example in various families of Lepidoptera, in tenthredinid Hymenoptera and in chrysomelid beetles) have more or less actively gregarious larvae, the intensity of this phenomenon varying from species to species. In the chrysomelids for example (e.g. Agelastica alni), larval clustering may be quite loose, several individuals simply feeding on the same leaf with no more than occasional contacts, whereas in other species (e.g. Phratora spp.), the groups are tight and permanent, and result from an active gregarious behaviour. We will focus on this particular type of true gregariousness, which seems to have evolved among several insect orders in this common habitat (the leaf surface), as a convergent adaptation to constraints such as plant defense (physical and chemical), predators and parasitoids, competition and overexploitation of food resources, adverse weather conditions.