Midwest Fish & Wildlife Conference 2019

AUTHORS: Macayla Greider, Jeffrey Dimick – Aquatic Biomonitoring Laboratory, University of Wisconsin-Stevens Point; Dr. Justin VanDeHey, Dr. Shelli Dubay – College of Natural Resources, University of Wisconsin-Stevens Point

ABSTRACT: Mermithid nematodes are generally considered as biological control agents for pest species like Anopheles, but also may influence Trout (Salmonidae) food sources because they cause reproductive failure and mortality in both midge (Chironomidae) larvae and mayfly (Ephemeroptera) nymphs.  However, much remains unknown about the mermithid life cycle and factors affecting their distribution. Our objectives were to determine if the prevalence of mermithid infections differed (1) between hosts with different feeding strategies, (2) in streams with different macroinvertebrate and fish communities, and (3) with stream flow rates. We hypothesized that (1) filter feeding midges would have higher prevalence of midge infection because filter-feeders passively ingest eggs whereas other midges seek out specific prey, (2) Trout streams would have fewer mermithids, and (3) stream flow would not be related to mermithid prevalence. Mermithid prevalence was assessed in samples collected from 48 streams during 2010-2014 from four northwestern Wisconsin counties. Infection was determined by observation of mermithids within midge bodies. Midges were identified to species to determine feeding behavior and distinguish filter feeders from non-filter feeders. Significantly lower proportions of mermithids were present in Trout streams than non-Trout streams, but no significant differences were present between mermithid presence and either HBI score or stream velocities. Chi-square analysis indicated no significant difference in prevalence between filter feeding and non-filter feeding groups; however, shredders had higher mermithid prevalence than other feeding groups. This research will provide insight into some aspects of mermithid life cycles and host selection.