Lucci-Rimer, Hayley, authorOde, Paul, advisorBalgopal, Meena, advisorBean, Dan, committee memberOcheltree, Troy, committee member2022-01-072022-01-072021https://hdl.handle.net/10217/234196Russian knapweed (Rhaponticum (=Acroptilon) repens) is a non-native plant species that has spread throughout the western United States, out-competing native and crop species. Two host-specific gall forming insects - the stem-gall wasp Aulacidea acroptilonica (Hymenoptera: Cynipidae) and the tip-gall midge Jaapiella ivannikovi (Diptera: Cecidomyiidae) - have been employed as biological control agents to manage its spread. However, the nature of the intra- and interspecific interactions between these two insect species is not fully understood even though this information is vital to successfully controlling Russian knapweed. Examining these interactions also contributes to a growing body of knowledge on plant-mediated indirect interactions, which are prevalent among herbivorous insects. To determine the nature of these interactions (e.g., positive, negative, or neutral) and the effects that the insects, together and separately, have on Russian knapweed, I performed studies in the greenhouse and at field sites throughout Colorado. I found evidence for a negative or neutral interspecific relationship, a negative or neutral intraspecific relationship among midges, and a positive or neutral relationship among wasps. The nature of these interactions is likely density and resource dependent. The associations between each insect species and measures of plant growth and reproductive capacity were mixed across the two studies, at times showing positive, negative, or neutral relationships. More studies that consider insect density, water availability, and resource allocation within Russian knapweed should be performed to better determine how the insects interact with one another and what their effects on Russian knapweed may be under varying conditions.born digitalmasters thesesengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.galling insectsinvasion biologynon-nativeindirect interactionsbiocontrolinvasive plantText