Restricted Gene Flow According to Host Plant in an Herbivore Feeding on Native and Exotic Watermilfoils (Myriophyllum: Haloragaceae)

Abstract

A native weevil is a candidate for biological control of the introduced aquatic weed Eurasian watermilfoil (Myriophyllum spicatum) in North America. Euhrychiopsis lecontei feeds on both the exotic Eurasian watermilfoil (EXO) and the native Northern watermilfoil (Myriophyllum sibiricum; NAT) in the United States. In theory, the ability of weevils that have shifted hosts to adapt to their new host species depends in part on restriction of gene flow between host races. We investigated components of gene flow between weevils on the two host plants. Weevils raised on the exotic EXO preferentially oviposited on EXO. Larvae tended to stay on the same host species when given the option to switch. Females had greater fecundity when raised on EXO than on NAT. Weevils raised on the native NAT oviposited on both plants. Thus, there is the potential for gene flow from NAT weevils into EXO weevil populations but less so in the reverse direction because of host fidelity. Gene flow is further reduced by the relatively lo...