The host range expansion of the specialist milfoil weevil, Euhrychiopsis lecontei, from the native Myriophyllum sibiricum (northern watermilfoil) to invasive M. spicatum (Eurasian watermilfoil) is one of the few examples of a native insect herbivore preferring, growing and surviving better on a nonindigenous host plant than it does on its native host plant. The milfoil weevil’s preference for the nonindigenous plant can be induced during juvenile development or through exposure to Eurasian watermilfoil as an adult. We evaluated how the fecundity of the milfoil weevil was affected over time by juvenile and adult exposure to the native, invasive and invasive × native hybrid milfoils and whether fecundity was correlated with host plant quality. Weevils reared on Eurasian watermilfoil laid more eggs than those reared on northern or hybrid watermilfoils. When weevils were collected from and exposed to milfoils collected directly from a lake, Eurasian-reared weevils had higher fecundity and greater preference for Eurasian over northern watermilfoil. When weevils were reared on and allowed to oviposit on milfoils grown in a common environment, the differences in fecundity and preference for Eurasian over northern or hybrid watermilfoils diminished. In Eurasian-northern experiments, milfoil weevils laid more than 80% of their eggs on Eurasian watermilfoil, but that value decreased when plants from common environments were used. Despite this preference, most weevils continued to use both hosts indicating that a complete host switch is unlikely. Weevils showed no oviposition preference between Eurasian and hybrid milfoils. The milfoil weevil had higher fecundity on Eurasian watermilfoil, which had a higher concentration of carbon, polyphenols and lignin than did northern watermilfoil, which had a higher concentration of ash. The milfoil weevil’s preference for Eurasian watermilfoil was affected by changes in plant chemistry, and ash appeared to act as a deterrent to oviposition on northern watermilfoil. The milfoil weevil can modify its response based on host-plant chemistry.
Bibliographical noteFunding Information:
Assistance with specimen collection and analyses were provided by many students at the University of Minnesota and Concordia College. C. Feldbaum (Konstanz) assisted with chemical analyses. We thank S. Weisberg for assistance with statistical analyses and model development and interpretation. The authors are grateful to three anonymous reviewers for their insightful comments on this manuscript. This work is the result of research sponsored by the Minnesota Sea Grant College Program supported by the NOAA Office of Sea Grant, United States Department of Commerce, under grant No. NOAANA16-RG1046. The U.S. Government is authorized to reproduce and distribute reprints for government purposes, notwithstanding any copyright notation that may appear hereon. Additional support was provided by the Minnesota Agricultural Experiment Station Hatch grant MIN-41-074, the University of Minnesota Graduate School, Concordia College Fugelstad-Torstveit Endowment Research Fund, and NSF S-STEM grant # 0850132 to H. Manning of Concordia College.
- Euhrychiopsis lecontei
- Host plant chemistry
- Hybrid milfoil
- Myriophyllum sibiricum
- Myriophyllum spicatum
- Oviposition preference and performance
- Specialist herbivore