Selection of biting sites on anuran hosts by Corethrella species

Once haematophagous insects reach their host, there is a still another vital step ahead, selecting a biting site. Optimal foraging theory predicts that biting insects should feed on their host on those areas that maximize blood intake while minimizing the costs. Here we investigate the biting sites of Corethrella species on three frog species that are attacked by the midges: túngara frogs, Engystomops pustulosus, and two species of treefrogs, Dendropsophus ebraccatus and D. microcephalus. The midges bite the small tree frogs on a variety of body areas including their back and legs, but they exclusively bite túngara frogs on their nostril. We explore the reasons behind such differences in biting sites examining the properties of the skin of these frogs. We used skin histological sections of the thoracic dorsum and nostril areas to examine skin characteristics of frog species. To determine the potential of the midges to bite such areas, we measured the length of the proboscis of midges attracted to the calls of each frog species. Results indicate that the skin of túngara frogs in their dorsum consists of a thickened epidermis followed by a dense dermis with multiple layers of connective tissues while it is thinner in the treefrogs. Most of the blood capilaries in the thoracic dorsum of túngara frogs locate under the thick connective tissues and are in far beyond the range of the probosis length of midges. Our study suggest that biting site preference of Corethrella midges is highly influenced by the properties of anuran skin.