Invasiveness of Some Biological Control Insects and Adequacy of Their Ecological Risk Assessment and Regulation

Rand

et al. 2007

Ecology

2001 -2003), the number of eggs laid by R. conicus on C. undulatum always decreased significantly with distance (0 -220 m) from a musk thistle patch. Neither the level of R. conicus oviposition on C. undulatum, nor the strength of the distance effect, were predicted by local musk thistle patch density or by local C. undulatum density (< 5 m). The results suggest that high R. conicus egg loads on C. undulatum near musk thistle resulted from the native thistle's co-occurrence with the co-evolved, preferred exotic host plant and not from the weevil's response to local host plant density. Mean egg loads on C. undulatum also were greater at sites with higher R. conicus densities. We conclude that both plant proximity and herbivore density strongly affected the herbivore-mediated indirect interaction, and that such interactions are important pathways by which invasive exotic weeds can indirectly impact native plants. (240 words)

Section: Indirect Effects Imposed By Invasive Speciesmentioning

confidence: 99%

Variation in Herbivore-Mediated Indirect Effects of an Invasive Plant on a Native Plant

Russell

Rand

et al. 2007

Ecology

“…In these prairies, R. conicus oviposits not only on wavyleaf thistle, but it also has heavily impacted a second, native thistle, Platte thistle (C. canescens Nutt.) Louda and Arnett 2000;Louda et al 2003;Rose et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Indirect interaction between two native thistles mediated by an invasive exotic floral herbivore

Russell

2005

Oecologia

., "Indirect interaction between two native thistles mediated by an invasive exotic floral herbivore" (2005). Faculty Publications in the Biological Sciences. 58. http://digitalcommons.unl.edu/bioscifacpub/58 AbstractSpatial and temporal variation in insect floral herbivory is common and often important. Yet, the determinants of such variation remain incompletely understood. Using 12 years of flowering data and 4 years of biweekly insect counts, we evaluated four hypotheses to explain variation in damage by the Eurasian flower head weevil, Rhinocyllus conicus, to the native North American wavyleaf thistle, Cirsium undulatum. The four factors hypothesized to influence weevil impact were variations in climate, weevil abundance, phenological synchrony, and number of flower heads available, either on wavyleaf thistle or on the other co-occurring, acquired native host plant (Platte thistle, Cirsium canescens), or on both. Climate did not contribute significantly to an explanation of variation in R. conicus damage to wavyleaf thistle. However, climate did influence weevil synchrony with wavyleaf flower head initiation, and phenological synchrony was important in determining R. conicus oviposition levels on wavyleaf thistle. The earlier R. conicus was active, the less it oviposited on wavyleaf thistle, even when weevils were abundant. Neither weevil abundance nor availability of wavyleaf flower heads predicted R. conicus egg load. Instead, the strongest predictor of R. conicus egg load on wavyleaf thistle was the availability of flower heads on Platte thistle, the more common, earlier flowering native thistle in the sand prairie. Egg load on wavyleaf thistle decreased as the number of Platte thistle flower heads at a site increased. Thus, wavyleaf thistle experienced associational defense in the presence of flowering by its now declining native congener, Platte thistle. These results demonstrate that prediction of damage to a native plant by an exotic insect may require knowledge of both likely phenological synchrony and total resource availability to the herbivore, including resources provided by other nontarget native species.

“…However, the release of exotic insects entails a risk to native plants and communities (Howarth, 1991;Simberloff and Stiling, 1996;Louda et al, 1997Louda et al, , 1998Stiling and Simberloff, 1999). Prediction of both the risk and the ecological impact of exotic insects poses a critical challenge (Louda, 1999a;Strong and Pemberton, 2000;Louda et al, 2003aLouda et al, , 2003b.…”

Section: Introductionmentioning

confidence: 99%

Chemistry of Cirsium and Carduus: a role in ecological risk assessment for biological control of weeds?

Jordon‐Thaden

Biochemical Systematics and Ecology

2003

Prediction of host plant range and ecological impact of exotic phytophagous insects, such as insects for classical biological control of weeds, represents a major challenge. Recently, the flowerhead weevil (Rhinocyllus conicus Fröl.), introduced from Europe into North America to control exotic thistles (Carduus spp.), has become invasive. It feeds heavily on some, but not all species of native North American thistles (Cirsium spp.). We hypothesized that such non-target use among native plants could be better predicted by knowledge of characteristic chemical profiles of secondary compounds to supplement the results of host specificity testing. To evaluate this hypothesis, we reviewed the literature on the chemistry of Cirsium and Carduus thistles. We asked what compounds are known to be present, what is known about their biological activity, and whether such information on chemical profiles would have better predicted realized host range and ecological effects of R. conicus in North America. We found an extensive, but incomplete literature on the chemistry of true thistles. Two main patterns emerged. First, consistent chemical similarities and interesting differences occur among species of thistles. Second, variation occurs in biologically active groups of characteristic compounds, specifically flavonoids, sterols, alkaloids and phenolic acids, that are known to influence host plant acceptance, selection, and feeding by phytophagous insects. Surprisingly, sesquiterpene lactones, which are characteristic in closely related Asteraceae, have not been extensively reported for Cirsium or Carduus. The minimal evidence on sesquiterpene lactones may reflect extraction methods vs. true absence. In summary, our review suggests further research on thistle chemistry in insect feeding is warranted. Also, since the exotic Canada thistle (Cirsium arvense) is an invasive thistle of current concern in North America, such research on mechanisms underlying host range expansion by exotic insects would be useful.