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AUTHORS: Macayla Greider, Aquatic Biomonitoring Laboratory, College of Natural Resources, University of Wisconsin-Stevens Point; Jeffrey Dimick, Aquatic Biomonitoring Laboratory, Wisconsin Cooperative Fishery Research Unit, University of Wisconsin-Stevens Point; Dr. Justin VanDeHey, College of Natural Resources, University of Wisconsin-Stevens Point; 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 mosquitoes, but also may influence Trout (Salmonidae) food sources because they cause mortality in both midge (Chironomidae) larvae and mayfly (Ephemeroptera) nymphs. Mermithid effects upon hosts include host reproductive failure and host death when mermithids complete their juvenile life stage and emerge from the host. Our objective was to identify environmental characteristics associated with mermithid presence in Wisconsin streams. In the Aquatic Biomonitoring Laboratory, midge microscope slides were examined and presence or absence of mermithid was recorded. We used data from 48 streams collected from 2010 through 2014 from Dunn, Polk, Barron, and St. Croix counties in northwestern Wisconsin. Logistic regression was used to compare stream characteristics including average velocity, mermithid prevalence among trout and non-trout streams, and Hilsenhoff Biotic Index (HBI) score, as well as year and location with presence or absence of mermithids within each stream. To date, we have found a significantly lower proportion of mermithids in Trout streams than non-Trout streams, but no significant difference in either HBI score or estimated velocities. Future analysis will include more abiotic factors, e.g. stream temperature, and other biotic factors like Trout or mayfly nymph abundance. This research will provide insight to the affects of mermithid presence on affect food webs within Wisconsin streams.