Nematode infection rates of Chironomidae subfamilies, functional feeding guilds and habit guilds within the Cheyenne River Basin, South Dakota

The Chironomidae occupy numerous niches in freshwater environments.  Mermithidae nematodes parasitize Chironomidae often leading to host mortality.  We investigated infection rates of Chironomidae subfamilies and functional feeding and habit guilds within streams of the Cheyenne River Watershed, South Dakota.  Nine sites were sampled 27 times following modified EPA EMAP protocols during the summers of 2007 and 2008.  Chironomidae were slide mounted and examined for nematode infection as indicated by a coiled mass in the body cavity.  An average of 167 (range = 3 to 534) midges were examined from each sample.  We observed an overall infection rate of 0.62% (n = 5026 total larvae).  Fifteen samples contained no parasitized midges.  Within-sample infection rates varied from 0-14.3% (mean = 1.1%).  Chironominae were the most commonly infected subfamily (0.82%) followed by Orthocladinae (0.54%) and Tanypodinae (0.16%).  Collector-filterers were the most commonly infected functional feeding guild (3.72%) followed by collector-gatherers (0.81%), shredders (0.49%) and engulfers (0.22%).  Climbers were the most commonly infected functional habit guild (2.34%) followed by burrowers (0.53%), clingers (0.47%) and sprawlers (0.31%).  Our infection rates were lower than previously reported findings, suggesting that larvae from our sites may be less stressed than those from previously reported streams.