Flies of the genus Culicoides are small, biting midges in the family Ceratopogonidae. These flies are of medical, veterinary, and economic importance because their blood-feeding behavior can cause stress to hosts and transmit disease agents. Despite the importance of these flies, little is known about their biology, especially the ecology of the immature stages and the phylogenetic relationships among taxa. The objectives of my study were to address these two areas of Culicoides biology.
Larval Culicoides were collected from aquatic habitats in four ecoregions of South Carolina, USA. Eleven ecological variables were recorded for each sample. Larvae were identified by amplifying and sequencing a portion of the COI gene by PCR and performing a BLAST search of an adult COI database. BLAST identifications were confirmed with morphological descriptions. Multiple logistic regression of the ecological variables was conducted on the presence-absence of larval taxa. Eleven species, 1 species complex, and 3 unidentified morphospecies of Culicoides were identified. Logistic regression yielded predictive models for C. furens (Poey), 1853, and C. hollensis (Melander and Brues), 1903. Culicoides haematopotus Malloch, 1915, was composed of five genetic clusters and two ecological groups, one present in shallow, aquatic habitats associated with hardwood forests and the other with shallow, aquatic habitats in the coast plains ecoregion, indicating a probable species complex. Two larval taxa with distinct morphologies were linked to C. stellifer (Coquillett), 1901, indicating another probable species complex.
Examination of Culicoides species for potential synapomorphies of the genus yielded two smooth, cuticular structures (scutal areolae) on the scutum just anterior to the scutellum. Scutal areolae were documented in males and females of seven genera of Ceratopogonidae. The scutal areolae were a synapomorphy of the family, with independent losses in the Forcipomyiinae+Dasyheleinae and the Ceratopogonini. In Culicoides and Paradasyhelea, the scutal areolae were modified into raised nodules, supporting a sister group relationship of these taxa. No pores, muscles, or nerves were associated with the scutal areolae, but the structures had light-reflecting properties, indicating a possible role in intraspecific communication.
The subgeneric classification of Culicoides was assessed using cladistic analysis. Morphological characters were extracted from the literature and used in a maximum parsimony analysis of the 13 subgenera and 7 species groups of Nearctic Culicoides. Five subgenera and one species group of Culicoides were monophyletic. Three subgenera were polyphyletic and no supporting synapomorphies were found for 10 subgeneric groups. A clade of the subgenera ((Avaritia+Hoffmania)+Culicoides) was inferred from the morphological analysis and confirmed by a maximum likelihood analysis of a fragment of the COI gene. Maximum likelihood analysis of an unresolved polytomy, using COI, did not result in improved resolution of the morphological tree, but indicated a species complex for C. stellifer, supporting results from the larval ecology study.