Master of Science (MS)
The Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), is considered one of the most destructive structural pests in the world, especially in warm and humid areas. Insecticide application is an effective strategy in termite control. In recent years, non-repellent insecticides have become popular for their high efficacy due to delayed toxicity and horizontal transfer. Fipronil (registered name Termidor®) and imidacloprid (registered name Premise®) have been applied to the perimeter of millions of houses in the United States. Fipronil and imidacloprid have different modes of action which may produce a synergistic effect when combined. There have been no studies on the toxicity interaction of fipronil and imidacloprid against termites including the Formosan subterranean termite. The original objective of the research was to determine whether combinations of the termiticides lead to enhanced toxicity against Formosan subterranean termites. Combinations of the non-repellent insecticides were treated on filter paper and sand for evaluation. After timed exposures, any living termites were transferred to untreated Petri dishes. Mortality of termites was recorded before and after the transfer. Lower mortality was observed when imidacloprid was mixed with fipronil compared to fipronil alone. Mortality was increased by the mixture over imidacloprid alone. To validate these results, more combinations were introduced in the second and third set of experiments. Besides the recording of mortality, the number of excavation holes made by termites in sand was also counted to determine whether excavation activity was related to mortality effects. A second objective was to seek a threshold level whereby the efficacy of fipronil becomes negatively impacted by imidacloprid presence. A threshold of between 15 and 25 ppm imidacloprid added to 100 ppm fipronil reduced the efficacy of fipronil. An increase in the number of excavation holes was significantly associated with a rising mortality, indicating imidacloprid affected the uptake of fipronil by reducing termite excavation behavior of treated soil. In practical terms and of potential concern for homeowners, the studies suggest that the efficacy of Termidor® applied around the perimeters of houses may be negatively affected by the presence of Premise®.
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Luo, Pan, "Toxicity interaction of fipronil and imidacloprid against Coptotermes formasanus" (2010). LSU Master's Theses. 1246.