ARS | Publication request: Relationships of host plant phylogeny, chemistry and host plant specificity of several agents of yellow starthistle

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 11, 2011
Publication Date: N/A

Technical Abstract: Plant species used for host specificity testing are usually chosen based on the assumption that the risk of attack by a prospective biological control agent decreases with increasing phylogenetic distance from the target weed. Molecular genetics methods have greatly improved our ability to measure genetic relatedness among test plants; however, biological control agents respond to the chemical, physical and behavioral characteristics of plants, rather than directly to their genetics. In general, phylogeny serves as a useful surrogate for the chemical, physical and behavioral (e.g., phenology, habitat) characteristics; however, convergent evolution could produce similar characters in distantly related plants, and divergent evolution could produce differences among closely related plants. Thus, relying only on phylogeny risks omitting a more distantly related plant that is vulnerable to attack. We analyzed the phylogenetic relationships of test plants in the tribe Cardueae which have been used to evaluate the specificity of prospective biological control agents of yellow starthistle, Centaurea solstitialis. The host plant specificity of prospective biological control agents mirrored phylogeny at a gross scale (tribe, subtribe), but not at a fine scale (subgenus). Furthermore, in laboratory choice and no-choice experiments, different species of insects posed risk to different nontarget plants, suggesting that they use different stimuli to identify their host plant. We extracted and analyzed volatile organic compounds (VOCs) to try to determine if they help explain host plant preference. Y-tube olfactometer experiments are also being conducted to determine if specificity can be measured with this method.