Effects of the organophosphorous insecticides temephos (Abate®) and chlorpyrifos (Dursban®) on populations of the salt-marsh snail Melampus bidentatus

The effects of 2 organophosphorous insecticides, temephos (Abate^®) and chlorpyrifos (Dursban^®), on populations of the salt-marsh snail Melampus bidentatus Say (Basommatophora: Melampidae) were investigated in a series of field experiments. These toxicants were aerially applied to mosquito breeding areas in New Jersey salt marshes in the manner normally used in biting-fly control operations. No significant change in the population density of M. bidentatus was observed in response to multiple treatments of granular formulations of either temephos or chlorpyrifos. However, there was a highly significant (P<0.01) depression in population density observed in the plot exposed to multiple treatments of a temephos emulsion. This depression was followed by a resurgence in density levels, beginning 3 weeks after the last treatment. The specific mechanism for thisperturbation is not known. However, it is hypothesized that it might involve some combination of indirect insecticide effects coupled with age-specific effects. Tests of age structure of the affected population using the chi-square distribution supported this hypothesis.Paper of the Journal Series, New Jersey Agricultural Experiment Station. This research was supported, in part, by a grant from the New Jersey Mosquito Control Commission.