FEEDING AND MATING IN THE INSECTIVOROUS CERATOPOGONINAE (DIPTERA)

The subfamily Ceratopogoninae (sensu Wirth, 1965a) is probably a natural (monophyletic) group but includes both blood sucking forms (Culicoidini) and predators on small insects. The insectivorous forms consist of a diversified array of six tribes and many genera represented in moist habitats throughout the world and especially abundant at lake margins.Many predator/prey observations are recorded. The prey consists almost exclusively of the males of other Nematocera or the smaller Ephemeroptera, which the female captures in flight by entering the male (mating) swarms of these insects and hovering until in a position to strike. The initial response is to the swarm-determining landmark, and the female hovers there whether or not potential prey is in flight; groups of hovering females can be induced artificially by suitable markers. These midges themselves form male swarms which the female enters for mating, and the unique method of hunting thus follows a pattern of behaviour already established in relation to another function. The insectivorous tribes have probably been derived from the more plesiomorphic Culicoidini, but the stages in the development of their radically different manner of hunting are not clear.The characteristic form of the mouthparts in the insectivorous genera is described and figured. The prey, after capture in flight, is usually held by the raptorial legs and quickly perforated by the mandibles. A proteolytic saliva is injected and the cellular tissue, except in the longer appendages, is liquefied and sucked out. In most species a single prey individual is not sufficient for one ovarian cycle, and the midge feeds several times. There is some degree of prey specificity, based at least in part on specific responses to the swarm-marker. In several genera there are long tubular "glands" in the abdomen, often everted in flight, whose function is not clearly established. Mobbing of the predator by the intended prey (mosquitoes) is described.The distinctive feature of mating is that the female, in addition to her other prey, often eats the male during mating. Nearly all the records come from the three tribes Heteromyiini, Sphaeromiini, and Palpomyiini. In these tribes (which probably form a relatively apomorphic monophyletic group) the male is usually a dwarf, and the plumose (auditory) antenna is more or less strongly reduced. It is suggested that the female remains in hunting phase when entering her conspecific swarm and captures the male as prey, and that the typical auditory recognition of female by male has become reduced or vestigial. In the more plesiomorphic tribes Ceratopogonini and Stilobezziini the male is normal in size and the antennal plume is fully developed, as in Culicoides, and there are only two records, at most, of the male being eaten during mating.The males eaten during mating are pierced through the head and reduced to an empty cuticle by the action of the lytic saliva. The terminalia however retain their hold, perhaps because of the early destruction of the suboesophageal ganglion, and the dry male cuticle often breaks away leaving the terminalia still attached. The structure of the terminalia and the mating position is described and discussed. Insemination is by spermatophore, which if the male is eaten never leaves the male duct. The terminalia of the male are inverted during mating and in some genera become so permanently early in adult life.An attempt is made throughout to view the phenomena in a phylogenetic context.Numerous illustrations are provided.