Indirect, plant mediated interactions of meristem miners on flower head feeders, a case for non-independence?

Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Biological Sciences.A long standing, dominant paradigm in the biological control of weeds is the independence of insect herbivore guilds' effects on their host plant. Recent work has shown stronger interactions among insect herbivore guilds than was previously expected. My research focuses on damage to apical meristems of tall thistles (Cirsium altissimum) by stem mining insects and the direct effects of this damage on plant architecture as well as the indirect, plant-mediated effects of this damage on flower head feeding insects and the arthropod predator community associated with tall thistle in south-central Kansas. Three questions are addressed; 1) What is the natural history of the predatory arthropod – tall thistle interaction in south-central Kansas? 2) Does apical meristem damage by insect herbivores influence host plant architecture, flower head damage and/or predatory arthropod densities? 3) Does plant architecture affect flower head damage and/or predatory arthropods? Two experiments were used to address those questions. The first experiment compared bolting tall thistles whose apical meristems were protected with insecticide with tall thistles whose apical meristems were not protected and were subject to herbivory. Damage to the apical meristem creates a plant that is shorter and has more flower heads than plants with the apical meristem intact and marginally increases primary branching. The second experiment modified the architecture of a bolting tall thistle with apical meristem damage back to a “pre-damaged” state by clipping lateral branches of the main stem. Neither experiment showed any significant difference in flower head damage severity or frequency, nor any differences in predatory arthropod densities among treatments. Through an overcompensation mechanism in the plant, meristem mining insects indirectly influence flower head feeding insects mediated by tall thistle. My results do not support the importation of multiple biological control agents for weed control