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

Potential habitats of immature tabanids in south-eastern Mendocino County, California, were investigated from March to July in 1971-1973. Funnel extraction, handsorting and sieve methods were used to examine 3421 soil samples 0.093 m2 in area X 8-10 cm deep from 5 major semi-aquatic 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. Semi-aquatic sampling yielded 1437 larval and pupal tabanids of 15 species in 4 genera (7 species of Chrysops, 2 of Hybomitra, 2 of Silvius and 4 of Tabanus). Seepage areas ranked first as to density and diversity, yielding an average of 15.3 immatures of 7 species/m2. Temporary pond margins yielded 14.4 immatures/m2, although only 25% 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 immature tabanids, even though they formed over 40% of all samples. Other potential habitats sampled in which few or no immature tabanids 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. Immature Chrysops were most abundant in habitats containing moderate to large amounts of decaying organic matter. The larvae of two species of Hybomitra were associated with organic substrata, principally mosses. Immatures of both species of Silvius were collected from sand and silt above the margins of lotic habitats. Species of Tabanus were adapted to a variety of habitats, as larvae of 3 of the 4 species collected inhabited 2 or more habitat types. T. punctifer O.-S. occurred in every kind of natural semiaquatic habitat sampled except tree holes.