The milfoil weevil Euhrychiopsis lecontei is a specialist aquatic herbivore that feeds, oviposits, and mates on the invasive freshwater macrophyte Myriophyllum spicatum. We characterized the weevil's preference for M. spicatum, and through bioassay-driven fractionation, isolated and identified two chemicals released by M. spicatum that attract E. lecontei. Mass spectrometry and nuclear magnetic resonance spectroscopy were used to identify the attractive compounds as glycerol and uracil. Dose-response curves for glycerol and uracil indicated that weevil preference increased as sample concentration increased. Weevils were attracted to a crude sample of M. spicatum-released chemicals from 0.17 to 17 mg/l, to glycerol from 18 to 1800 μM (0.0017-0.17 mg/l), and to uracil from 0.015 to 15 μM (0.00014-1.4 mg/l). Although glycerol and uracil are ubiquitous, weevils are likely responding to high concentrations that are released as a result of the rapid growth of M. spicatum. Uracil concentration was greater in the exudates of M.spicatum than other Myriophyllum spp. E. lecontei was attracted to glycerol at a concentration similar to that at which terrestrial insects are attracted to sugar alcohols. This is the first example of a freshwater specialist insect being attracted to chemicals released by its host plant. Analysis of the water milfoil-weevil interaction provides further understanding as to how insects locate their host plants in aquatic systems.
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Acknowledgments—We thank Elisabeth M. Gross for the gift of tellimagrandin II and Frank R. Stermitz for analysis of alkaloid content. We are grateful to Tom Krick, Letitia Yao, Beverly Ostrowski, and LeeAnn Higgins for assistance and advice with the mass spectral and NMR analyses. We thank M. Moody for molecular identification of Myriophyllum spp. Assistance with specimen collection and analyses were provided by D. Ward, C. Lemmon, S. Daugherty, S. Coloso, J. Dehn, K. Eichstaedt, C. McCollum, and K. Mann. We thank LeeAnn Higgins and two anonymous reviewers for their comments on the manuscript. This work is sponsored by the Minnesota Sea Grant College Program supported by the NOAA Office of Sea Grant, United States Department of Commerce, under grant no. NOAA-NA16-RG1046. The U.S. government is authorized to reproduce and distribute reprints for government purposes, not withstanding any copyright notation that may appear hereon. Additional support was provided by the Minnesota Agricultural Experiment Station and the University of Minnesota Graduate School. This paper is journal reprint no. JR 511 of the Minnesota Sea Grant College Program.
Copyright 2008 Elsevier B.V., All rights reserved.
- Aquatic plant-herbivore interactions
- Chemical attractant
- Euhrychiopsis lecontei
- Freshwater macrophyte
- Host location
- Myriophyllum spicatum
- Specialist herbivore