| Complex food web interactions are important ecological factors in terrestrial ecosystems. Generalist predators frequently engage in complex food web interactions such as omnivory, intraguild predation, and secondary predation. In this dissertation, the interactions between specialist and generalist natural enemies of herbivorous arthropods in the cotton agroecosystem are examined.; In chapter 1, releases of the predatory mite, Galendromus occidentalis , are evaluated for spider mite control in organically and conventionally managed commercial cotton fields. Results showed that releases did not increase predatory mite populations nor substantially reduce spider mite populations.; In chapter 2 and 3, the compatibility of predator releases with the conservation of resident natural enemies is studied. I quantify the impact of generalist predators, Geocoris and Orius, and the omnivore Frankliniella occidentalis on the establishment of the predatory mite Galendromus and how these predator-predator interactions influence spider mite control. Field experiments showed that in the absence of generalist predators, released predatory mites could establish large populations and suppress spider mite populations. Geocoris and Orius had a strong negative impact on predatory mite populations but Frankliniella had no impact. However, despite the negative effect of predators on predatory mites, spider mite population suppression was improved by generalist predators. My studies suggest that adding Galendromus to the cotton agroecosystem with spider mites and generalist predators may create an unstable intraguild predation system where predatory mites are excluded, as predicted by theory.; In chapter 4, the impact of introducing a predator, Hippodamia convergens, on the biological control of the cotton aphid, Aphis gossypii, by the parasitoid Lysiphlebus testaceipes under field conditions is studied. Hippodamia substantially reduced immature parasitoid populations. Despite the negative impact of Hippodamia on aphid parasitoids, aphid population suppression was greatest in treatments containing both Hippodamia and parasitoids. The parasitoid alone or in combination with Hippodamia suppressed cotton aphids in a density-dependent manner and increased plant biomass. It is concluded that under conditions where a predator shows both a partial preference for unparasitized hosts and high levels of predation on unparasitized hosts, we may expect the predator to improve suppression of herbivores even if it produces high levels of intraguild predation. |
