The systematics and ecology of the British psychodidae associated with aquatic habitats.

The thesis makes a distinct contribution to knowledge of both the systematics and the ecology of the species of psychodidae associated with aquatic habitats. The systematic work (Section I) was carried out as a necessary precursor to ecological investigation, aiming at the precise identification of every individual encountered. In this section there are descriptions of new species, and of previously unknown larvae and pupae; revised descriptions of other species, and some information on geographical variation. The problem or species pairs in the Family psychodidae is discussed at length. It is shown that Pericomu trivialize and P.nubila are true species, and that there are no grounds for considering these and the members of other species pairs as cases of male dimorphism, or any other than long established species. In section II an account is given of the ecology of the larvae and adults of species described in the first half of the thesis, considered from a number of new aspects. Several congeneric species normally occur together in the same breeding area, and although there is often a degree of spatial isolation between the larvae of these species, there are examples in which the larvae appear to live together in exactly the same microhabitat. Species of Pericoma and Telmatoscopus are all either univoltine, bivoltine or trivoltine, and there is a well defined seasonal succession of species. Larval adaptation is considered, with particular emphasis on the structure of the mouthparts. It is shown that the same adaptive features often arise independently in a number of separate evolutionary lines. Information is given on the adaptive significance of many structural characteristics, including reduction of setation, and the form of the mandible, labrum, hypostome and other mouthparts.