Growth, Abundance and Distribution of Larval Tabanids in Experimentally Fertilized Plots on a Massachusetts Salt Marsh

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Abstract
(1) Tabanus nigrovittatus and Chrysops fuliginosus, two of the four species of tabanid larvae found on Great Sippewissett Marsh comprised approximately 90% of the total larval tabanid population and were both predominantly found in areas where the short form of Spartina alterniflora was the dominant plant. (2) The average larval densities for both Tabanus nigrovittatus and Chrysops fuliginosus found in the control plots of 1972-3 and the 1974 plots are comparable to the maximum values for Tabanus nigrovittatus obtained elsewhere on the east coast of North America. Larval tabanid populations were drastically reduced in plots treated with a sewage sludge fertilizer but were unaffected by treatments with a phosphate and a urea fertilizer. (3) Analysis of monthly larval size classes for the 1972-3 sampling period indicates that the larval life of T. nigrovittatus probably lasts two years. Summer growth rate is about 4 mm/month. (4) T. nigrovittatus feeds on most soft-bodied insect larvae found on the marsh and also on the amphipod Orchestia grillus. (5) Larval densities were reduced in laboratory experiments from 80-240/m2 to 40-120/m2 through cannibalism, the lower figure approximating the densities of larval tabanids found in the field.