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Trophic Interactions and the Efficacy of Milfoil Weevils for Biocontrol Of BearWorks MSU Graduate Theses Spring 2016 Trophic Interactions And The Efficacy Of Milfoilee W vils For Biocontrol Of Eurasian Watermilfoil In Wisconsin Lakes Kristopher Andrew Maxson As with any intellectual project, the content and views expressed in this thesis may be considered objectionable by some readers. However, this student-scholar’s work has been judged to have academic value by the student’s thesis committee members trained in the discipline. The content and views expressed in this thesis are those of the student-scholar and are not endorsed by Missouri State University, its Graduate College, or its employees. Follow this and additional works at: https://bearworks.missouristate.edu/theses Part of the Biology Commons Recommended Citation Maxson, Kristopher Andrew, "Trophic Interactions And The Efficacy Of Milfoilee W vils For Biocontrol Of Eurasian Watermilfoil In Wisconsin Lakes" (2016). MSU Graduate Theses. 13. https://bearworks.missouristate.edu/theses/13 This article or document was made available through BearWorks, the institutional repository of Missouri State University. The work contained in it may be protected by copyright and require permission of the copyright holder for reuse or redistribution. For more information, please contact [email protected]. TROPHIC INTERACTIONS AND THE EFFICACY OF MILFOIL WEEVILS FOR BIOCONTROL OF EURASIAN WATER-MILFOIL IN WISCONSIN LAKES A Masters Thesis Presented to The Graduate College of Missouri State University In Partial Fulfillment Of the Requirements for the Degree Master of Science, Biology By Kristopher Andrew Maxson May 2016 Copyright 2016 by Kristopher Andrew Maxson ii TROPHIC INTERACTIONS AND THE EFFICACY OF MILFOIL WEEVILS FOR BIOCONTROL OF EURASIAN WATER-MILFOIL IN WISCONSIN LAKES Biology Missouri State University, May 2016 Master of Science Kristopher Andrew Maxson ABSTRACT Eurasian water-milfoil (Myriophyllum spicatum L., henceforth “EWM”) is the most heavily managed nuisance submersed aquatic plant in the United States. EWM’s rapid spring growth and formation of dense surface mats inhibits native macrophyte communities, serves as poor-quality habitat for fish and macroinvertebrates, impacts recreation, and can clog water supply infrastructure. The milfoil weevil (Euhrychiopsis lecontei Dietz) has been associated with EWM declines in several states, though natural weevil densities are generally too small to effect control. Augmentative biocontrol has had varied success and fish predation may account for high weevil mortality. Weevils were augmented in 4 northern Wisconsin lakes in summer 2013. In summer 2014, I collected invertebrates associated with EWM plus 442 bluegill (Lepomis macrochirus Rafinesque) diet samples from the 4 study lakes. Overall, chironomids and oligochaetes were the dominant invertebrates associated with plants, while chironomids and Daphnia spp. constituted up to 27.2% and 24.0% of the fish diets, respectively. Milfoil weevils were found in 2.9% of diet samples examined. Weevil larvae were preyed upon more frequently than adults (94.2% of weevils consumed) and sometimes occurred in high numbers within single diet samples. Since the larval stage contributes the most to EWM damage, selective predation on this stage may limit its use as a control agent. KEYWORDS: Eurasian water-milfoil, Myriophyllum spicatum, milfoil weevil, Euhrychiopsis lecontei, biological control, bluegill, Lepomis macrochirus, diet This abstract is approved as to form and content _______________________________ John E. Havel, Ph. D. Chairperson, Advisory Committee Missouri State University iii TROPHIC INTERACTIONS AND THE EFFICACY OF MILFOIL WEEVILS FOR BIOCONTROL OF EURASIAN WATER-MILFOIL IN WISCONSIN LAKES By Kristopher Andrew Maxson A Masters Thesis Submitted to the Graduate College Of Missouri State University In Partial Fulfillment of the Requirements For the Degree of Master of Science, Biology May 2016 Approved: _________________________________________ John E. Havel, Ph. D. _________________________________________ Daniel W. Beckman, Ph. D _________________________________________ Day B. Ligon, Ph. D. _________________________________________ Julie J. Masterson, Ph. D., Dean, Graduate College iv ACKNOWLEDGEMENTS Work on this project would not have been possible without the help from a great many people. First and foremost, I would like to thank the P.I.s on the project, my research advisor Dr. John Havel and Dr. Susan Knight with UW-Trout Lake. Your aid in experimental design and securing funding for the project has proven invaluable. Your passion and dedication to your fields is truly an inspiration, and I hope one day to be half the naturalist I’ve seen in you. I would also like to thank my committee, Dr. Day Ligon and Dr. Dan Beckman as well as Dr. John Heywood for advice on experimental design and statistical analysis. The aid of Dr. Greg Sass with Wisconsin DNR was invaluable during early stages of project design and fish sampling, as well as edits to thesis drafts. I am forever indebted to Adrienne Gemberling, Alex Bauch, Paul Schramm, Willis Perley, Paul Schilke, and the “Weevil Crew” (Erick Fruehling, Jim Miazga, Chris Winter, and Nick Winter). Your aid during late night electrofishing runs, SCUBA diving through dense macrophyte beds, and long days flushing fish stomachs is a testament to your dedication and passion for the field. Credit is also due to the many Trout Lake undergraduates, graduate students, and staff members who provided support in innumerable ways. Because of you, my time spent in the Wisconsin northwoods will forever hold a place in my heart. I would likely still be picking through invertebrate samples had it not been for Ann Wempe. My gratitude for her aid in process sampling and data entry cannot be fully expressed. Thanks also to Stephanie Sickler. Without her efforts in aging fish scales, the scales collected during my study would likely have remained in their envelopes. The many graduate students of Missouri State University, who shared in the ups and downs of graduate school, will never be forgotten. I can think of no better group with whom to share this journey. My journey through graduate school would not have been possible without the love and support of my parents, Stephen and Tammy Maxson, twin sister, Courtney Lorenz, and many family and friends from home. Through church collections and food donations, you ensured that I had a car that still ran and filled my pantry with more than Ramen noodles. Last but not least, I would like to thank my fiancé, Stacey Jackson, for her continued love, support and patience during my tenure in the “wrong Springfield.” There is no other person whom I would wish by my side. Funding for this project was provided by grants from the Wisconsin Department of Natural Resources to S. Knight and J. Havel (ACE-122-12 and AIRD-100-14), a faculty research grant to J. Havel, and thesis funding and summer fellowship from Missouri State University to K. Maxson. Summer housing at Trout Lake Station was provided by the University of Wisconsin-Madison. v TABLE OF CONTENTS Introduction ......................................................................................................................... 1 Methods............................................................................................................................. 11 Study Sites ............................................................................................................ 11 Fish Sampling ....................................................................................................... 12 Fish Processing ..................................................................................................... 13 Environmental Sampling ...................................................................................... 14 Sample Analysis.................................................................................................... 15 Weevil Densities ................................................................................................... 16 Prey Preference ..................................................................................................... 16 Results ............................................................................................................................... 19 Fish Collected for Diet Samples ........................................................................... 19 Taxonomic Composition of Fish Diet Samples .................................................... 20 Weevils in Diet Samples ....................................................................................... 21 Taxonomic Composition of Environmental Samples ........................................... 21 Prey Preference ..................................................................................................... 22 Discussion ......................................................................................................................... 24 Impacts of Dense EWM on Sunfish Populations .................................................. 24 Multiple Effects from Chemical and Mechanical Control of EWM..................... 25 The Role of Milfoil Weevils in Controlling EWM ............................................... 25 Fate of Milfoil Weevil Populations....................................................................... 26 Weevil Densities in the Environment ................................................................... 27 Weevils in Bluegill Diet Samples ........................................................................
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