Density and diversity of immature Tabanidae (Diptera) in relation to habitat type in Mendocino County, California.

Abstract

Potential habitats of immature Tabanidae in southeastern Mendocino County, California, were investigated from March to July 1971–1973. Funnel extraction, handsorting and sieve methods were used to examine 3421 soil samples 0.093 m2 (=1 ft2) × 8–10 cm deep from 5 major semiaquatic habitats (in seepage areas and above the margins of creeks, permanent ponds, temporary ponds and the Russian River) and terrestrial habitats (oak woodland leaf litter and soil). These habitats are described and compared with respect to the density and diversity of their tabanid inhabitants. Semiaquatic sampling yielded 1437 larval and pupal tabanids of 15 species in 4 genera (7 Chrysops spp., 2 Hybomitra spp., 2 Silvius spp., 4 Tabanus spp.). Seepage areas ranked 1st as to density and diversity, yielding an average of 15.3 immatures/m2 of 7 species. Temporary pond margins yielded 14.4 immatures/m2 to rank 2nd, although only 1/4 of those sampled were productive. The borders of creeks produced the lowest density (2.8 immatures/m2) and those of temporary ponds the lowest diversity (4 species). Woodland leaf litter and soil samples yielded no tabanid immatures, although they comprised over 40% of all samples. Other potential habitats sampled in which few or no tabanid immatures were found included decaying logs, stock water troughs and tree holes. Four of the 7 species of Chrysops reared were each restricted to 1 habitat type. Chrysops species were most abundant in habitats containing moderate to large amounts of decaying organic matter. The larvae of Hybomitra spp. “A” and “B” were associated with organic substrata, principally mosses. Immatures of both Silvius species were collected from sand and silt above the margins of lotic habitats. Tabanus species were adapted to a variety of habitats, as larvae of 3 of the 4 species collected inhabited 2 or more habitat types. T. punctifer Osten Sacken occurred in every kind of natural semiaquatic habitat sampled except tree holes.