Applied ecology and control of imported fire ants and Argentine ants (Hymenoptera: Formicidae)
Wiltz, Beverly Anne
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The red imported fire ant, Solenopsis invicta Buren, and Argentine ant, Linepithema humile (Mayr), are invasive species that are major pests in urban, natural, and agricultural habitats. The goal of this dissertation was to study aspects the chemical sensitivity, behavior, and ecology of each species to enhance control options. In these studies, I: 1) provide recommendations for the optimal usage of various insecticides against each species, 2) evaluate deterrent and toxic effects of natural products, 3) develop a delivery system for ant toxicants that uses a pheromonal attractant to facilitate toxicant transfer by contact, and 4) determine which habitats within blackland prairies are most susceptible to invasion by imported fire ants. Bifenthrin had properties best suited for use as barrier or mound treatments against both species. In laboratory assays, it was the fastest acting of the chemicals tested and was the only chemical that acted as a barrier to ant movement. Fipronil exhibited high horizontal toxicity and delayed topical toxicity, properties that are desirable in a broadcast treatment. Chlorfenapyr and thiamethoxam appeared best suited to use as mound treatments, as they had low horizontal toxicity and did not impede ant movement in barrier tests. At least one of the four tested rates of basil, citronella, lemon, peppermint, and tea tree oils were repellent to both ant species. In continuous exposure assays, citronella oil was toxic to both species, and peppermint and tea tree oils were toxic to Argentine ants. Of the semiochemicals tested, only triolen, a component of the red imported fire ant brood recognition pheromone, enhanced removal of treated granules by S. invicta workers. At a rate of 0.06% fipronil plus triolein, there was 90.5% mortality in laboratory colonies versus 46.5% with the same rate of fipronil without triolein. Ground surveys and analysis of remotely sensed images were conducted for two sites in northeastern Mississippi, both of which contain S. invicta x S. richteri hybrid imported fire ants. Mound densities were highest and individual mounds were smallest in disturbed areas. Fire ants were not found in forest or chalk outcrop plots or in prairie containing > 26% tree cover.