Behavioral Toxicology of the Eastern Subterranean Termite, Reticulitermes flavipes (Kollar) (Isoptera:Rhinotermitidae)

Abstract

The eastern subterranean termite Reticulitermes flavipes (Kollar) is one of the most economically important termite species in the United States. Behavioral toxicology has become very relevant in the control of termites because the non-repellent compounds used are specifically designed to exploit behavioral biology of termites for optimum performance. To describe insecticide-induced behaviors, termites were exposed continuously to filter paper that had been treated with 200 ppm indoxacarb, 50 ppm fipronil, 300 ppm chlorantraniliprole, and distilled water (i.e., control treatment). The neurotoxins, fipronil and indoxacarb elicited toxicity symptoms that progressed from incipient intoxication, through ataxia, and moribundity which culminated in death. Chlorantraniliprole-treated termites did not exhibit ataxia but remained on their feet and became increasingly lethargic until they became moribund. Termites were exposed to 45, 90, 135, and 180 ppm (w/w) of indoxacarb-treated soil for 5, 10, 20, 40, 80, and 160 min to test for effects on onset of abnormal behaviors. Earlier onset of abnormal behaviors was observed at higher concentrations and longer durations of exposure to indoxacarb at both individual and group levels. Termites in the walking and tunneling studies were exposed to filter paper treated with fipronil (1, 10, and 50 ppm) and indoxacarb (50, 100, and 200 ppm) for 10 min. Total distance walked in 60 s was measured at 2-h intervals until cessation of walking. Distance walked remained fairly constant in the control treatments but declined significantly in the insecticide-treated termites. In termites treated with 100 ppm indoxacarb, the first significant decline occurred in 8 h (from 77.95 ± 3.81 cm to 41.92 ± 7.40 cm [F = 24.66, df = 7, P < 0.0001]) but it took only 2 h to decline from 73.70 ± 3.19 cm to 58.43 ± 3.80 cm (F = 165.29, df = 7, P < 0.0001) in termites treated with 200 ppm indoxacarb. A similar trend was observed among fipronil-treated termites. Tunneling ability was tested in transparent cylindrical plastic containers containing untreated soil (18% moisture w/w). Untreated termites constructed more and longer tunnels (P < 0.05) compared to those treated with insecticides. Distance tunneled by termites declined with time after exposure to indoxacarb (F = 6.16, df = 7, P < 0.0001) and fipronil (F = 6.04, df = 7, P < 0.001). Our results show that well-defined abnormal behaviors can be used in quantitative assessments of toxicity and thus complement mortality in the assessment of insecticide performance.