Revealing the native status of Conyza bonariensis: Specialization of insect herbivores associated with Conyza and Erigeron spp. (Asteraceae) in Louisiana, Texas and Mississippi

Flaxleaf fleabane, Conyza bonariensis (L.) Cronquist (Asteraceae), is an annual herb which grows up to 1.0 m in height. Considered native to the Americas, C. bonariensis is a major weed in Australia and other countries; partially due to widespread herbicide resistance. The purpose of this study was to catalog herbivorous insects associated with C. bonariensis in Louisiana, Texas and Mississippi, and to identify potential biological control agents. We predicted that the native status of C. bonariensis will result on the presence of host-specific insects in southern United States. Field surveys were conducted to identify insects associated with C. bonariensis and closely related species: C. canadensis [(L.) Cronquist], Erigeron annuus (L.), E. philadelphicus (L.), and E. procumbens [(Houst. ex Mill.) G.L. Nelson]. Leaves, roots, stems, and flowers of plants were inspected for signs of insects and/or pathogens. Results revealed the presence of Halticus bractatus (Say) (Miridae) and Corythucha marmorata (Uhler) (Tingidae) attacking the stem, leaves, and pedicels; Calycomyza sp. (Agromyzidae) attacking the leaves; and Pteriphoridae, Gracillariidae, and Tortricidae attacking the flowerheads, leaves, and stem tips. A common garden experiment was conducted to attract and catalog insects to a plot containing both Conyza and Erigeron species. Insect occurrence, feeding guilds, host association, and feeding damage was recorded. Survey and common garden results will help determine insect host specificity and field population densities of these herbivores. Promising candidates for biological control will be imported into a quarantine facility in Brisbane, Australia to conduct host specificity studies.
Keywords: biological control, herbicide resistance, host specificity