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Evolution has contributed to the successful invasion of exotic plant species in their introduced ranges, but how evolution affects particular control strategies is still under evaluation. For instance, classical biological control, a common strategy involving the utilization of highly specific natural enemies to control exotic pests, may be negatively affected by host hybridization because of shifts in plant traits, such as root allocation or chemical constituents. We investigated introgression between two parent species of the invasive shrub tamarisk (Tamarix spp.) in the western United States, and how differences in plant traits affect interactions with a biological control agent. Introgression varied strongly with latitude of origin and was highly correlated with plant performance. Increased levels of T. ramosissima introgression resulted in both higher investment in roots and tolerance to defoliation and less resistance to insect attack. Because tamarisk hybridization occurs predictably on the western U.S. landscape, managers may be able to exploit this information to maximize control efforts. Genetic differentiation in plant traits in this system underpins the importance of plant hybridization and may explain why some biological control releases are more successful than others. [ABSTRACT FROM AUTHOR]

Spurgia capitigena is a gall midge that has been released as a biological control agent of leafy spurge ( Euphorbia esula), a noxious rangeland weed in North America. We isolated 15 microsatellite loci from S. capitigena with from two to 27 alleles at each locus. These markers will allow us to examine the structure and levels of neutral genetic variation in native and introduced populations. [ABSTRACT FROM AUTHOR]

Abstract: The distribution of phytophagous insects is influenced by their preference for and performance on their host plants. Biological control agents of invasive plants that prefer and perform better on their target hosts are more likely to be both effective and safe.Brachypterolus pulicarius is an herbivore used in North America to combat two invasive plants, yellow toadflax and Dalmatian toadflax (Linaria vulgaris and Linaria dalmatica). Adult beetles prefer yellow toadflax over Dalmatian toadflax, and when beetles are redistributed onto Dalmatian toadflax, populations do not consistently establish. This leads to the hypothesis that beetle larvae will perform best on yellow toadflax. A reciprocal transfer experiment was conducted to test this hypothesis. Development rate, pupal mass and percent survival were measured to assess larval performance. Development time was influenced by an interaction between the source host and the test host, a pattern suggesting that it is important to consider both the collection host and redistribution host when releasing this beetle for the control of toadflax. Pupal mass of larvae reared on yellow toadflax was, on average, 13% greater than that of larvae reared on Dalmatian toadflax, supporting the hypothesis. Survival rate was not significantly influenced by source host, test host, or their interaction, suggesting that survival rates will be similar no matter the combination of collection host and redistribution host. These results, along with the preference that adult beetles show for yellow toadflax, do not support the redistribution of B. pulicarius onto Dalmatian toadflax in North America. [Copyright &y& Elsevier]

Abstract: Many researchers have hypothesized that reduced genetic diversity in introduced populations of biological control agents can compromise the agent’s ability to establish and then adapt to novel environments. Strategies such as collecting from a wide geographic area or maintaining large colony sizes through the quarantine process have been used to minimize the loss of genetic diversity. Few studies have examined how the process of collection, quarantine, and establishment could affect patterns of genetic diversity in biological control agents. In this paper, we examine patterns in neutral genetic diversity in Spurgia capitigena, a gall midge introduced as a biological control agent of leafy spurge (Euphorbia esula) from its original collection site in Italy, a newly discovered population of the midge from southern France, and in two established populations in North America. By comparing the existing populations with historical samples collected shortly after the original introductions in 1991, we found that there is evidence of a mild bottleneck in both of the introduced populations. Further, we also examined the population structure in European populations of the fly collected from leafy spurge and a closely related species, cypress spurge (Euphorbia cyparissias) and found evidence for local restrictions in gene flow between populations on the two plants, but no evidence to support the current taxonomy of the genus with two distinct fly species. [Copyright &y& Elsevier]