COMPARATIVE-STUDY OF MOUTHPARTS OF PREDACEOUS MIDGES OF THE TRIBE PALPOMYIINI (DIPTERA, CERATOPOGONIDAE) FROM EASTERN UNITED-STATES

Mouthparts of females of 16 species and males of 13 species representi ng Bezzia, Phaenobezzia, and Palpomyia of the insectivorous tribe Palp omyiini were examined by light and scanning electron microscopy. Great est differences among species occurred in the sclerotized mandibles of females where the mean number of coarse medial teeth ranged from 6.00 to 10.31, small basal teeth from 0.37 to 3.47, length of the tooth ro w in relation to length of the mandible from 14.9 to 29.8% and mean nu mber of lateral teeth from 1.50 to 6.61. An interlocking mechanism mid length of the blade functions as a-fulcrum; abduction of the base of t he mandibles results in divergence of their tips and enables their str ong teeth to cut the cuticle of the prey. The non-insectivorous males have mandibles with large medial non-functional teeth and lack an inte rlocking mechanism. Lateral teeth are present on the mandibles of some males of eight species. The unarmored labrum, hypopharynx and lacinia are inserted into the wound made by the mandibles. The mandibles rema in between the labrum and hypopharynx during feeding and serve as the floor of the food canal and roof of the salivary canal. The laciniae, which are smooth in both sexes, form the lateral proximal boundaries o f the food canal. Cylindrical structures at the tip of the labrum of f emales are thought to be mechanoreceptors, chemoreceptors or both; the y are reduced in size or absent in males and, in most species, are rep laced by spicules. Labra of males and females have species specific ch aracters, but differences are less pronounced in males. The hypopharyn x of females is generically specific in its shape and species specific in distribution of its spicules. The hypopharynx of males is species specific in size and shape of its spicules which are longer than in th ose of conspecific females. Sensilla on the maxillary palp sensory org an are species specific in both sexes with respect to number, points o f origin on the palp of individual sensilla, shape of the head of the sensilla and total length. The number of sensilla per sensory organ is approximately equal in both sexes of a given species and they probabl y do not function in prey detection and/or location, which is thought to be more related to visual stimuli in predaceous midges.