Seasonal abundance of aquatic Diptera in two oligohaline tidal marshes in Mississippi

Nineteen species of Diptera (16 in each zone) from 7 families were found in monthly collections (June 1979 through May 1980) in 2 Mississippi marsh plant zones dominated by Juncus roemerianus and Spartina cynosuroides, respectively. The Juncus zone was dominated by a species of the Palpomyia-Bezzia complex, 2 species of Bezzia (Ceratopogonidae), Paratendipes sp., Limnophyes, sp. (Chironomidae) and Thinophilus frontalis (Dolichopodidae). Palpomyia-Bezzia sp., Culicoides hollensis, Ormosia sp. (Tipulidae) and Pelastoneurus abbreviatus (Dolichopodidae) dominated the Spartina zone. Among other species found in small numbers were the tabanids Chrysops atlanticus and Tabanus nigrovittatus, the ephydrid Notiphila bispinosa and an unidentified anthomyiid. Total insect density and species richness were lowest in June and July in both zones, corresponding to a pulse of adult emergence. Overall, total density was significantly higher in the Spartina zone with mean values of 165 and 245 insects/m2 for the Juncus and Spartina zones, respectively. In addition to total density, differences in abundance were apparent for a number of species between marsh zones. Patterns could be attributed to species-specific habitat preference, predation by aquatic predators and/or by interactions of the infauna themselves.