This document is a combination of two articles previously submitted to the journal, Sociobiology. Lethal dose of fipronil was determined in two experiments: topical application and contact with treated sandy loam. In the topical application the toxicity of fipronil was evaluated against workers of a laboratory colony of Coptotermes formosanus Shiraki. Fipronil was applied by the microsyringe to the dorsum of the abdormen at a rate of 0.1µl acetone solution to afford a worker individual with a desired dose of fipronil (0.1, 0.5, 1.0 or 5.0 ng/worker). Three replicates, each consisting of 30 workers, were prepared for each dose (0.1, 0.5, 1.0 and 5.0 ng/worker). Thirty topically treated workers of the same dose group were kept in a glass Petri dish (9 cmø) with a water-moistened cotton pad adhered inside the lid to determine LT100s and LT50s based on the change in termite mortality with time, and this assay was conducted again. LT100s/LT50s were 81/69, 37/23, 26/8, 8/5 h for 0.1, 0.5, 1.0 and 5.0 ng/worker, respectively in the first bioassay. In the second bioassay, those were 80/62, 35/25, 27/10 and 10/6 h. The results clearly supported the dose dependence of fipronil on the termite mortality. The estimated LD100s/LD50s after 12 h that were calculated from the data on LT100s and LT50s were 4.11/0.87 and 4.53/0.93 ng/worker in the first and the second bioassays, respectively. In the second experiment (soil contact test), the amount of fipronil recovered from dead termite workers of Coptotermes formosanus Shiraki was chemically determined. Termite workers were kept in contact with the fipronil-treated sandy loam for 24hours. The mean amount of fipronil recovered from the body exterior of a worker was 3.10 ng, ranging from 0.32 to 8.36 ng. The mean amount recovered from the body interior was 3.17 ng, with a range of 1.39-6.49 ng. Accordingly, the total amount of fipronil recovered from a single worker ranged from 2.52 to 12.64 ng, with a mean of 6.27 ng. Since the mean value was higher than the previously estimated LD100 (4.11-4.53ng) at 12 hours when fipronil was topically applied, most of the tested termites were dead during the exposure to treated sandy loam.1

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