The biological control program for diffuse knapweed, Centaurea diffusa Lamarck, a Eurasian plant that has invaded large areas of grasslands in western North America, has gone on for over 35 years. This program involved the release of 12 biological control agents of which four are numerous and widely distributed; two species of Tephritid flies, Urophora affinis and Urophora quadrifasciata, the r...

Little is known about how exotics influence the ecophysiology of co-occurring native plants or how invader impact on plant physiology may be mediated by community diversity or resource levels. We measured the effect of the widespread invasive forb spotted knapweed (Centaurea maculosa) on leaf traits (leaf dry matter content, specific leaf area, leaf nitrogen percentage, leaf C:N ratios, and del...

Five insect biological control agents that attack flower heads of spotted knapweed, Centaurea stoebe L. subsp. micranthos (Gugler) Hayek, became established in western Montana between 1973 and 1992. In a controlled field experiment in 2006, seed-head insects reduced spotted knapweed seed production per seed head by 84.4%. The seed production at two sites in western Montana where these biologica...

Theresponses and impacts ofÞve insect species that feedonCentaureadiffusaLamarck, diffuse knapweed, to soil nitrogen and phosphorus additions were studied in grasslands east of the ColoradoFrontRange.Wepredicted that fertilizationwasunlikely tohave adirect effect onherbivory but that if the insects preferentially select vigorous plants, increased tissue nitrogen, plant density, or plant mass re...

Invasive plants have devastating effects on ecosystems and biodiversity that early intervention can prevent. Eradication or containment of new invasions is difficult to achieve because of constraints posed by the low density and detectability of individuals. Domestic dogs trained to cue on distinctive scents might provide an effective method to detect spotted knapweed. The objective of this stu...

Abundances and interactions among biological control insects and their effects on target invasive plants were monitored within the flower heads and roots of diffuse knapweed, Centaurea diffusa, and in spotted knapweed, Centaurea stoebe, along the Colorado Front Range. Flower weevils, (Larinus species) and root-feeders (Cyphocleonus achates and Sphenoptera jugoslavica) were released on knapweed ...

Theory and empirical work have demonstrated that diverse communities can inhibit invasion. Yet, it is unclear how diversity influences invader impact, how impact varies among exotics, and what the relative importance of diversity is versus extrinsic factors that themselves can influence invasion. To address these issues, we established plant assemblages that varied in native species and functio...