PARENT SESSION
Oral Session #77: Aquatic Ecology: Food webs, invertebrates. Presiding: R.A. Washington-Allen.
Friday, August 10, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.

Variation in the response of the milfoil weevil to native and exotic watermilfoil host-plant cues.

MARKO, MICHELLE¹, NEWMAN, RAYMOND¹, GLEASON, FLORENCE¹, ¹

ABSTRACT- The weevil Euhrychiopsis lecontei (Curculionidae) is a specialist herbivore on watermilfoils that has recently undergone a host range expansion from its native host, Myriophyllum sibiricum (Haloragaceae), to Eurasian watermilfoil, Myriophyllum spicatum. In fact, the weevil prefers the introduced plant, Eurasian watermilfoil, to its native host, northern watermilfoil, and appears to use chemical cues to select its host plant. Two-way choice tests were conducted with watermilfoil meristems, washings from Eurasian watermilfoil and isolated fractions in order to assess the chemical mediation of this host range expansion. Weevils preferred Eurasian watermilfoil to both the control and northern watermilfoil (Sign test, p<0.01 for both tests) and preferred Eurasian watermilfoil exudates to a control (p<0.01). However, the weevils did not exhibit a preference for northern watermilfoil over a control (p>0.01). Weevil preferences among Eurasian watermilfoil populations were tested with plants collected from different lakes throughout the greater Minneapolis, MN metro area. Weevil preference for Eurasian watermilfoil collected from different lakes varied over the season. Thus, the ecology of the weevil-milfoil interaction is complex and the role of chemistry in that interaction requires further analysis. Determination of the identity of the chemical cues and factors that influence seasonal variation is needed to understand the chemical mediation of this host range expansion and the potential of the weevil as a biological control agent.

KEY WORDS: Myriophyllum spicatum, Euhrychiopsis lecontei, host range expansion