Theory predicts that, upon release from natural enemies in the new range, invasive species will evolve to allocate more resources towards traits that improve their ability to compete with native species. The motivation for most biological control programs is to re-introduce native enemies in order to oppose this effect and reduce or even reverse some of the negative impacts of invasive species on native and economically important ecosystems. In many cases, multiple biocontrol agents are introduced, often under the assumption that their impacts will be complementary. However, studies that attempt to quantify the nature of interactions among biocontrol agents tend to find unique outcomes: as yet, no general patterns have emerged. Here I describe the findings of a study of the impacts of the introduction of one species of biocontrol agent of invasive purple loosestrife, the leaf beetle Neogalerucella almariensis, on the reproductive success of a second biocontrol agent, the flower-feeding weevil Nanophyes marmoratus. Somewhat surprisingly, I found that more adult weevils tended to emerge from plants that were simultaneously infested with both types of beetles. This was true even when differences in flower number among plants were taken into account. Moreover, there were more aborted flowers on an inflorescence where both biocontrol agents were present. Finally, more pollinators visited the plants that were infested by both biocontrol agents. The observational data also show a positive correlation between the presence of the leaf beetle larvae and the number of adult flower weevils found on an inflorescence. I discuss various explanations, including the possibility that biocontrol-induced changes in flowering phenology and plant nutritional compounds could be, at least partially, responsible for these findings.

In the first part of this study we monitored the development of biological control of purple loosestrife Lythrum salicaria over a six-year period at Morgan Lake in western Oregon. In 1992, two beetles, Galerucella pusilla and G. calmariensis (Coleoptera: Chrysomelidae), were released to control the wetland weed at this test site. Our purpose was to estimate quantitative performance parameters that might be generally applied in monitoring biological weed control. Our six performance measures were: 1) biological control agent establishment, 2) the rate of increase of the agents, 3) the rate of spread of the agents, 4) the effect of the agents on individual target plants, 5) the effect of the agents on the population of the target plants, and 6) the indirect impact of the biological control agents on the local plant community. The beetles established viable populations that increased during the study with an intrinsic rate of increase (r), based on the growth rate in damage, estimated at 2.24/year. Within six years after introduction, the beetles spread to saturate the entire purple loosestrife habitat (4100 m��) around the lake. The rate of spread, estimated by calculating a diffusion coefficient (D), was 57.5 m��/year. Adult beetles made seasonal, exploratory movements up to 30 m away from the host plant stand into surrounding crop fields, which suggests a disturbance-free buffer should be established in the habitat surrounding the loosestrife stand. By 1997, both flowering success and median stem density (per 0.125 m�� plot) of purple loosestrife declined to zero. Mean above-ground biomass decreased to 8.4% of its 1994 level. Biomass of native plant species increased by only 3% between 1996 and 1997. Overall, G. pusilla and G. calmariensis reduced the abundance of the target plant at our site. Our monitoring methods were effective at quantitatively measuring the establishment, increase, spread, and damage of the biological control agent, the subsequent decline of the target plant, and the impact on the local plant community. The second part of our study used field and greenhouse experiments to assess non-target effects of two introduced biological control organisms (Galerucella pusilla Duftschmid and G. calmariensis L.: Chrysomelidae) on the economically important ornamental plant, crape myrtle (Lagerstroemia indica L: Lythraceae). Prior host specificity tests performed in the laboratory found that beetles fed, but were unable to complete their life cycle, on this non-target plant. However, there was concern over damage that might occur when the two plant species existed together. This study extended prior tests into a field environment in order to compare the physiological host range revealed in greenhouse tests with the ecological host range revealed in the field. We assumed, based on prior evidence, that the control agents would not complete development on the non-target plant, and therefore, when the non-target organism was isolated from populations of the target organism the direct effects of the biological control agents would be negligible. When the target and non-target organisms existed together, the magnitude of indirect effect of the target organism on the non-target organism via the control agent was expected to increase with: 1) decreasing distance between the target and non-target organisms, and 2) increasing dispersal capability of the control agents. As expected from prior studies beetle feeding and oviposition occurred on crape myrtle but the beetles could not complete development on this non-target plant in our greenhouse and field tests. Leaf damage inflicted by the beetle was lower on crape myrtle than on purple loosestrife plants used as controls and extensive defoliation to the non-target plant was limited to within 30 m from the edge of the purple loosestrife stand. Biomass of crape myrtle was significantly reduced near the stand compared with plants that remained relatively untouched at greater distances. Purple loosestrife biomass exhibited a greater reduction with decreasing distance from the source of beetle colonization. In this thesis we construct and implement strategies for quantitatively assessing success of biological control programs and risk of introduced biological agents to non-target organisms. Through these observations and experiments we hope to increase the predictability and safety of biological control programs. / Graduation date: 1998

Two European leaf-eating beetles, Galerucella calmariensis L. and G. pusilla (Duft.)(Chrysomelidae:Coleoptera) were released at four sites in Quebec to manage the semi-aquatic exotic weed, purple loosestrife (Lythrum salicaria L.). Protocols for monitoring the Galerucella populations and detecting changes in the plant communities were implemented. In addition, the effect of seeding with native plants species in conjunction with Galerucella herbivory was tested in an experiment at a purple loosestrife stand in Ontario. Releases of lab-reared beetles in Quebec in 1996 did not survive to 1997 at any of the 4 sites, but releases of field collected beetles in 1997 overwintered successfully at 3 of the 4 sites. The density of purple loosestrife in 1998 ranged from 28% (Cap Tourmente) to 84% (Hull). The density of Galerucella in 1998 ranged from 6 (Lac St Francois) to 50 (Hull) adults/m 2/min. In the Ontario experiment, herbivory and seeding together interacted to increase the biomass of other plant species significantly---and thereby reduced the dominance (proportion of the biomass) of purple loosestrife---but did not have a significant effect on the biomass of purple loosestrife in the first season.

Thesis (M.S.)--Ohio State University, 1986. / Includes bibliographical references (leaves 102-106). Available online via OhioLINK's ETD Center

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Thesis (M.E.S.)--The Evergreen State College, 2006. / Title from title screen (viewed 3/11/2010). Includes bibliographical references (leaves 41-53).

The release of biological control agents into the environment is inherently risky: assessment of those risks through on-going, post-release monitoring is very important. Herbivores have the potential to inflict multiple impacts on a host plant’s performance and reproduction. Previous research demonstrates that the effects of herbivory on plants include changes to plant architecture, biomass allocation, flowering time and reproductive success, to list a few. Moreover, when herbivory significantly impacts the population ecology of a dominant community member, other species can be indirectly affected, ultimately influencing plant community ecology. Here I describe an investigation into the impacts of two introduced herbivorous biological control agents: the leaf beetle Galerucella calmariensis (Coleoptera: Chrysomelidae), and the flower-feeding weevil, Nanophyes marmoratus (Coleoptera: Brentidae) on several characteristics of the host plant species, invasive purple loosestrife (Lythrum salicaria), and its surrounding community. I collected data on 18 invaded communities from around eastern Ontario, including information on feeding damage and the density of each species of biological control, along with data on purple loosestrife’s height and biomass, inflorescence length, inflorescence number and fruit production. The history of each site’s colonization by Galerucella was also considered. I discovered that the density of both Galerucella and Nanophyes at a site was negatively associated with Lythrum fruit production. However, herbivore density was not significantly associated with Lythrum biomass, height or the species richness of the surrounding plant community. This study, conducted 20 years after the initial Ontario release of Galerucella, demonstrates that although vegetative traits of Lythrum do not appear to be significantly impacted by the presence of Galerucella or Nanophyes, reproductive traits are. Twenty years is likely too short a time period to adequately assess the impacts of the release on community species richness, although my data indicate that communities with smaller Lythrum plants tend to have higher species richness. This study covered a small geographical area and data collection was conducted for a single season only; adding additional years and/ or sites is recommended.

Galerucella pusilla and G. calmariensis have provided successful biological control of purple loosestrife (Lythrum salicaria L.) in non-tidal areas but only marginal control in areas of tidal influence. While a previous study identified mechanical scour by tidal waters as the main cause of establishment failure, purple loosestrife stem density explained more than 80% of the variability in presence and absence of Galerucella at my study sites in the Columbia River Estuary. A logistic regression model using purple loosestrife stem density, elevation, and their interaction as predictors accurately predicted 92.5% of Galerucella presence or absence observations of a test data set (n= 201). Field data also identified a critical threshold of approximately 32 purple loosestrife stems/m2 , above which Galerucella were present 100% of the time at the release sites.