Abstract

Mile-a-minute weed, Persicaria perfoliata (L.) Gross, formerly known as Polygonum perfoliatum L., is an invasive annual vine that established in the United States in the late 1930s and has since spread to eleven states ranging from Massachusetts to West Virginia. The USDA approved the release of Rhinoncomimus latipes Korotyaev (Coleoptera: Curculionidae) for biological control of mile-a-minute in 2004. Weevil adults feed on mile-a-minute foliage; the larvae feed within stems at nodes and may cause sufficient damage to reduce seed production. In this study, weevil dispersal, establishment, and impact were evaluated at three replicated release arrays in Chester County, Pennsylvania. Monitoring points located on concentric circles surrounding the point of release were checked for two years post-release. The following was recorded for each 1 m ² monitoring quadrat: number of weevils, total number of damaged nodes, presence or absence of eggs, percent cover of mile-a-minute, percent feeding damage by weevil adults, and the number of mature and immature fruiting terminals.

The weevils established at all three release sites. Weevils were active from early spring through hard fall frosts and completed at least three to four generations per year. Both years, the proportion of monitored mile-a-minute quadrats that contained eggs decreased from an average of 60% in late August to zero in early October, before a substantial temperature drop but coincident with a decrease in day length: an average of 60% of quadrats had eggs at 14.5 hours of day light, 30% at 12.5 hours, and 0% at ∼11 hours. The average intrinsic rate of increase of the weevil population was estimated at 2.08 in 2005 and 5.03 in 2006, which is comparable to or exceeds that of other successful biological control agents. Mile-a-minute seed cluster production was lower at two of the three sites in 2006 compared to 2005. Weevils dispersed up to 200 m away four months post-release. Weevils were found in mile-a-minute patches nearly 800 m from the release within 14 months; dispersing weevils located both large mile-a-minute populations and small isolated patches. Based on the results of this study, the weevil has a high potential to be an effective biological control agent for mile-a-minute weed.