PARENT SESSION
Oral Session # 89: Insect Ecology II.
Presiding: R Sears
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 101.

Chemically mediated host-plant selection by the milfoil weevil: A freshwater insect-plant interaction.

Marko, Michelle^*,1, Gleason, Florence¹, Newman, Raymond¹, ¹ University of Minnesota, Saint Paul, MN

ABSTRACT- To an insect, the air contains a myriad of chemical messages that signal the location or presence of predators, mates and host plants. In aquatic systems, the medium of water, rather than air, contains these chemical messages, which are readily broken down by microorganisms. The goal of this research was to determine whether aquatic insects can use chemical cues to locate their host plants. We have determined that the native weevil Euhrychiopsis lecontei has made a host-range expansion from the native northern watermilfoil, Myriophyllum sibiricum, to the non-indigenous Eurasian watermilfoil, Myriophyllum spicatum. The weevil performs better on the invasive Eurasian watermilfoil and behavioral bioassays indicate that the weevil uses chemical cues released by Eurasian watermilfoil to select its hostplant. Lyophilized water from jars containing field-collected milfoil was used to determine the level of weevil attraction to milfoil exudates with a dose-response curve (Regression; p<0.001, R²=0.97). Bioassay-driven fractionation (Y-tubes) of watermilfoil exudates was used to isolate and identify the attractive fraction. Anion exchange, sizing, and reverse-phase high performance liquid chromatography were used in the fractionation. Chemical ionization-mass spectroscopy and ¹H and ¹³C nuclear magnetic resonance were used to identify the components of the attractant, which are common metabolites. Weevil response to each of the components was determined. This is the first isolation of a water-borne insect attractant in freshwater systems. Analysis of the watermilfoil-weevil interactions will provide further understanding as to how insects locate their host-plants both in aquatic and terrestrial systems and how host-range expansions develop.

Key words: Eurasian watermilfoil, Euhrychiopsis lecontei, host-plant location, host-range expansion