USE OF COARSE WOODY DEBRIS BY DIPTERA IN OZARK STREAMS, ARKANSAS

Aquatic dipterans were sampled from coarse woody debris (CWD) and ston y benthic habitats from February 1991 through February 1992 in the Whi te River, Illinois River, and Clear Creek of the Ozark Plateau in Arka nsas. Chironomidae was the numerically dominant taxonomic group, and t hey were collected in significantly greater densities from CWD than fr om benthic habitats; but densities of other dipterans did not differ s ignificantly between habitat types. Representatives of five taxa were collected in significantly greater densities from benthic habitats, an d seven from CWD. The greatest estimated mean density of dipterans occ urred during the spring, but differences were not significant because of high variation within seasons. The degree of decay of CWD was an im portant microhabitat factor for representatives of six taxa, of which four were xylophagous chironomids. The xylophages that were affected b y degree of decay were Brillia flavifrons, Polypedilum fallax, Stenoch ironomus sp., and Xylotopus par. Eukiefferiella spp. and Phaenospectra sp. were the non-xylophages affected by decay stage. Biofilm volume a ppeared to be a less important factor in CWD use, but was important fo r representatives of two taxa (B. flavifrons and Eukiefferiella spp.).