Growth, abundance and distribution of larval tabanids in experimentally fertilized plots on a Massachusetts salt marsh.
Larvae of Tabanus nigrovittatus Macq. and Chrysops fuliginosus Wied., 2 of the 4 species of tabanid that breed in the Great Sippewissett Marsh in Massachusetts, comprised about 90% of the total larval tabanid population in 1972-74 and were found predominantly in areas in which the short form of Spartina alterniflora was the dominant plant. The average larval densities for both species found in untreated plots were similar to the maximum values of T. nigrovittatus obtained elsewhere on the east coast of North America. Larval populations were very greatly reduced in plots treated with a sewage-sludge fertiliser but were unaffected by treatments with a phosphate and a urea fertiliser. Analysis of classes of larval size by month for the period March 1972 to December 1973 indicated that the larval stage of T. nigrovittatus probably lasts 2 years. The summer growth rate was about 4 mm/month. Larvae of T. nigrovittatus fed on most soft-bodied insect larvae found in the marsh and also on the amphipod Orchestia grillus (Bosc). Larval densities were reduced in laboratory experiments from 80-240/m2 to 40-120/m2 through cannibalism, the lower figure approximating to the densities of larval tabanids found in the field.