Toxicological studies on the long-term effects of heavy metals (Hg, Cd, Pb) in soil on the development of Aiolopus thalassinus (Fabr.) (Saltatoria: Acrididae)

Abstract

Long-term effects of soil treated with 0.12–12 ppm HgCl 2, 2–100 ppm CdCl 2 and 25–500 ppm PbCl 2 on the development, reproductive capacity and viability of Aiolopus thalassinus (Fabr.) (grasshoppers) during two successive generations were studied. The hatching rate of nymphs developed from eggs laid in treated soil was significantly reduced. Mercurywas the most effective in reducing the hatching rate followed by cadmium and lead. The newly hatched nymphs, which developed in the heavy-metal-treated soil, were transfered to and reared in separate cages in order that toxicological effects could be followed through the next two generations without any further treatment. No significant increase was observed in percent mortality during both the F 1 and F 2 nymphal stages resulting from Hg, Cd and Pb treatment. The nymphs were more tolerant than the eggs and adults to the cumulative effect of heavy metals. The mean durations of the F 1 and F 2 nymphal stages were prolonged in all Hg and Cd treatments, but such a prolongation in the Pb treatments was found only in F 1 nymphs, those developed from the two highest soil PbCl 2 concentrations (250 and 500 ppm). The adult fresh weight of the F 1 and F 2 generations was significantly low in the case of the Hg and Cd treatments. The lifespan of the F 1 and F 2 adults developed from eggs laid in Hg-. Cd- and Pb-treated soil was significantly shortened and thus the number of egg pods was reduced in comparison with the control. The hatchability of nymphs developed from eggs laid by the F 1 generation was significantly lower than that of the untreated control. No significant decrease in the hatching rate was found for the eggs laid by the F 2 generation, except at the highest soil concentrations of the three metals. The metal content of eggs laid by the F 1 generation increased significantly with increasing soil concentrations of the three metals. In the F 2 generation eggs the heavy metal content was reduced in all cases; this indicates a dilution of the metal concentration in successive generations if no further exposure takes place.