FUNCTIONAL-MORPHOLOGY OF THE MANDIBLES OF THE LARVAE OF EPISYRPHUS-BALTEATUS (DE-GEER, 1776) (DIPTERA, SYRPHIDAE)

Aphidophagous syrphid (Diptera: Syrphidae) larvae have no structures f or seizing and killing such as prehensile legs and strongly sclerotize d external mouthparts enabling them to capture and feed on their prey. Nevertheless they are considered to be efficient predators. In order to understand this paradox in Episyrphus balteatus, 2 complementary ap proaches were followed. These consisted of, first, a careful analysis of the morphology of mouthparts of the larvae, and second, an investig ation of their feeding behaviour. The mouthparts were found to be comp osed of 2 groups of dental sclerites, corresponding to the 2 inner ele ments of the cephalopharyngeal skeleton. The exterior elements or tria ngular sclerites are absent in the first-instar larvae. These elements appeared close to the mouth in the second and the third-instar larvae , were oriented in the opposite direction to the other elements, and w ere positioned laterally. This structure probably serves to anchor the anterior part of the predator within the prey, thus preventing it fro m escaping. During the feeding activity, the seizing process occurred immediately after the recognition. The lifting-up behaviour of the fir st-instar larvae is probably due to the absence of the triangular scle rites. The suction was marked by an active movement of the cephalophar yngeal skeleton and a peristaltic movement of the abdomen. The feeding time was inversely proportional to the larval development. (C) 1998 E lsevier Science Ltd. All rights reserved.