Different acute toxicity of fipronil baits on invasive Linepithema humile supercolonies and some non-target ground arthropods.

Fipronil is one of the most effective insecticides to control the invasive ant Linepithema humile, but its effectiveness has been assessed without considering the genetic differences among L. humile supercolonies. We hypothesized that the susceptibility of the ant to fipronil might differ among supercolonies. If so, dosage and concentration of fipronil may need to be adjusted for effective eradication of each supercolony. The relative sensitivities of four L. humile supercolonies established in Hyogo (Japan) to fipronil baits were examined based on their acute toxicity (48-h LC(50)). Toxicities of fipronil to seven ground arthropods, including four native ant species, one native isopoda, and two cockroaches were also determined and compared to that of L. humile supercolonies using species sensitivity distributions. Marked differences in susceptibility of fipronil were apparent among the supercolonies (P < 0.008), with the 'Japanese main supercolony' (271 µg L(-1)) being five to ten times more sensitive to fipronil than other colonies (1183-2782 µg L(-1)). Toxicities to non-target species (330-2327 µg L(-1)) were in the same range as that of L. humile, and SSDs between the two species groups were not significantly different (t = -1.389, P = 0.180), suggesting that fipronil's insecticidal activity is practically the same for L. humile as for non-target arthropods. Therefore, if the invasive ant is to be controlled using fipronil, this would also affect the local arthropod biodiversity. Only the 'Japanese main supercolony' can be controlled with appropriate bait dosages of fipronil that would have little impact on the other species.

Gas-phase disproportionation of nitric oxide at elevated pressures.

T.P. Melia's chemical kinetics study of the disproportionation of nitric oxide (NO), 3NO --> NO2 + N2O, (Melia, T.P. (1965) J. Inorg. Nucl. Chem., 27, 95-98), which is the most quoted quantitative investigation presently available, revealed a rather strong dependence of the effective rate constant, Kk' of Melia's third-order rate law, -d[NO]/dt = Kk'[NO]3, on the initial pressure of NO. In order to estimate extent of accumulation of NO2 and N2O as a function of time by integration of the rate law, we have evaluated the dependence of the effective rate constant as a function of pressure and thus as a function of time on the basis of the non-ideality of NO gas. Although our approach is crude in that the non-idealities of NO2 and N2O and other NOx products and a probable deviation of the gas mixture from the Dalton's law have not been considered, it provides a means for approximately estimating the rate of accumulation of NO2 and N2O based on Melia's data. According to these calculations, the extent of the disproportionation is generally negligible at low initial pressures, e.g. 5 atm or less, while at 200 atm, the mole fractions of NO2 and N2O can become as high as 12-13% only after 10 days. These values are alarmingly high for handling pressured NO- in N2-mixture in either research or clinical settings. This information must be borne in mind when compressed NO in commercial cylinders is employed in high precision experiments. Disproportionation of NO under pressure also deserves attention in inhalation of low doses of NO in the treatment of diseases characterized by pulmonary hypertension and hypoxemia.