Semester of Graduation

Fall 2021

Degree

Master of Science (MS)

Department

Entomology

Document Type

Thesis

Abstract

Flaxleaf fleabane [Conyza bonariensis (L.) Cronquist] (Asterales: Asteraceae) is an annual herb which grows up to 1.0 m in height and is native to South America. Due to introduction and subsequent development of herbicide resistance, C. bonariensis has become a major agricultural weed in Australia. The purpose of this study was to catalog herbivorous insects associated with local populations of C. bonariensis in Louisiana, Texas and Mississippi in order to establish comparisons with the Australian fauna and identify potential biological control agents. Leaves, roots, stems, and flowers of C. bonariensis were inspected for signs of insects and pathogens. Results revealed the presence of numerous Hemipterans, including Halticus bractatus [Say] (Miridae), Lygus lineolaris [Palisot de Beauvois], and Taylorilygus apicalis [Fieber] attacking the stem, leaves, or pedicel. An agromyzid fly, Calycomyza humeralis [von Roser] was also found attacking the leaves. In addition, field surveys included the exploration of close relatives of C. bonariensis, including C. canadensis [(L.) Cronquist], Erigeron philadelphicus (L.), and E. procumbens [(Houst. ex Mill.) G.L. Nelson]. These surveys resulted in the finding of several insect species, including Hypera postica [Gyllenhal] and Listroderes difficilis [Germain] (Coleoptera: Curculionidae). A gall forming midge, Neolasioptera erigerontis [Felt 1907] was found associated with C. canadensis and seemed to show a high level of host specificity. Outcomes of this survey determined the host specificity, field population densities and type and degree of damage of these insects.

Two types of common garden experiments were conducted during the study. These experiments took place at the LSU, Burden Botanical Museum and Garden in Baton Rouge, Louisiana. The first experiment looked at the community and diversity of herbivorous insects associated with C. bonariensis, C. canadensis, E. Philadelphicus, as well as how these plant species developed over time. The results of this experiment showed that both Conyza spp. had steady growth rates during the early summer months of June and July, when this experiment took place. E. philadelphicus, being a species that grows and flowers more during the mid to late spring season, these plants did not show a difference in the rate of growth during this experiment. Additionally, it was seen that more insects were found associated with the two Conyza spp. than with the Erigeron sp. Both Conyza sp. grow larger than the Erigeron sp., and unlike the two Conyza spp., E. philadelphicus does not produce multiple axial branches from its main stem that could provide more food for herbivorous. The second experiment was an exclusion study looking at how the lack of various biotic stressors (pathogens and herbivorous insects) affected the growth and development of C. bonariensis. The results of this experiment seem to show that there was no difference in the development and growth of plants whether treated with insecticide, fungicide, a combination an insecticide and fungicide, or treated with a water control. From this experiment, it seemed that plants treated with the water control were healthier than those treated with any other treatment. Despite being attacked by both insects and pathogens throughout the study, most plants treated it with the water control had a darker green coloration, which is seen healthy C. bonariensis plants.

Committee Chair

Diaz, Rodrigo

Included in

Entomology Commons

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