Distribution and development of immature salt marsh Tabanidae (Diptera)

A study plot measuring 54 000 m2 on Cat Island in the Housatonic River in Connecticut was systematically sampled in order to determine the distribution of the larvae of Chrysops fuliginosus Wied., C. atlanticus Pechuman and Tabanus nigrovittatus Macq. in a regularly flooded salt marsh with Spartina alterniflora as the predominant plant. Of the 96 soil samples washed, 64.5% contained larvae of C. fuliginosus, while only 14.6% yielded C. atlanticus and 17.7% T. nigrovittatus. C. fuliginosus had a highly contagious distribution and coexisted with the other 2 species in 11 soil samples. There was a significant negative correlation between the numbers of C. fuliginosus and distance from drainage ditches. The occurrence of larvae of C. atlanticus was significantly correlated with salinity and organic content of the soil samples, and immature stages of this species were collected from very wet depression areas bordering drainage ditches. Immature stages of T. nigrovittatus were abundant throughout the open marsh in surface sediments that contained accumulations of wet matted vegetation, but larval distribution was not correlated with soil salinity. Both large and small larvae of C. fuliginosus and T. nigrovittatus were present in the marsh in all seasons, and this and the inability of relatively small larvae to pupate in the laboratory suggest that some larvae of these species take at least 2 years to mature.