Establishment of Hylobius transversovittatus Goeze (Coleoptera: Curculionidae), a biological control agent of purple loosestrife, in Virginia

Abstract

Abstract Hylobius transversovittatus Goeze (Coleoptera: Curculionidae), an exotic root feeding weevil, has been released in the USA and Canada for biological control of purple loosestrife Lythrum salicaria L. (Lythraceae), an aggressive emergent aquatic weed of Eurasian origin that has replaced native wetland vegetation. Questions have remained about the establishment and impact of this agent on purple loosestrife in North America. In this report, we present the first detailed account of the establishment and impact of H. transversovittatus in Coeburn and Goshen, Virginia. The weevil was imported from Germany. Adults of H. transversovittatus (n=53) and eggs (n=3935) were first released in Coeburn between 1992 and 1994. After the site was dredged in 1995, 512 eggs were placed in plants in 1995/96, followed by a release of 30 adults in 1999. In Goshen, 19 adults and 2800 eggs were released from 1994 to 1996. Adult weevils were placed on plants at the center of an infested field and eggs were placed in plants or in soil near roots. Establishment was based on digging whole plants and examining roots for larvae. In Coeburn, recovery of H. transversovittatus larvae ( X =0.33 larva per root) was first detected in 1994 at the original release site and larvae were found in roots 400 m downstream of the release point in 2000. Thirteen percent of the roots excavated (n=135) were infested with H. transversovittatus. In Goshen, H. transversovittatus larvae were first detected in 1997 with 2% of the roots infested ( X =0.02 larva per root, n=60). By 2000, the infestation rate increased to 28%. Dry weights of infested and noninfested roots at each site were not different. There was also no difference in mean dry root weight of purple loosestrife between the two sites. Excavation of roots to determine the presence and quantity of H. transversovittatus larvae is laborious but it is more accountable than searching for adults or eggs. H. transversovittatus is well established at both sites in Virginia.