Abstract The ecological impact offour insecticides used to control desert locustswas investigated during experimental field trials in natural temporary ponds in a cultivated savannah area of Senegal, West Africa. The insecticide formulations, dose rates, and application techniques were similar to those used in operational desert locust control. Average initial concentrations of fenitrothion, diflubenzuron, deltamethrin, and bendiocarb in pond water were 80, 10.4, 0.45, and 24.0 μg/L, respectively. Diflubenzuron and deltamethrin virtually disappeared in 24 h. Pseudo–first-order half-lives were 34 h for fenitrothion and 17 d for bendiocarb. Fenitrothion and deltamethrin significantly reduced population densities of backswimmers of the genus Anisops (Hemiptera, No-tonectidae) and in addition caused an extensive kill of other species of insects. Both insecticide applications were also followed by reductions of zooplankton densities, especially Cladocera, and deltamethrin eradicated populations of fairy shrimp (Streptoce-phalus spp.: Branchiopoda, Anostraca). Diflubenzuron only affected crustaceans, i.e., cladocerans and fairy shrimp. The least harmful insecticide in the study was bendiocarb, which only reduced the density of cladocerans. Recovery proceeded at fixed rates, which were different for each taxon. Anisops spp. recovered from the treatments in 1 to 4 weeks, most likely through aerial migration. Cladocerans returned to normal densities in 3 to 6 weeks. Streptocephalus spp., however, whose resting eggs presumably need desiccation during the dry season to be able to hatch, did not reappear until the next rainy season, one year later. It is concluded that contamination of temporary ponds in the Sahel by insecticide drift from desert locust control operations with any of the four insecticides should be avoided.
(1) Population differentiation in the collembolan Orchesella cincta (L.) under the influence of metal soil pollution was studied by measuring Pb and Cd excretion efficiency in individual Collembola from various sites. (2) Total and exchangeable fractions of Pb, Cd, Zn, Cu, Fe and Ca were determined in the A-horizon of forest soils at ten locations in the Netherlands, Belgium and Germany. Concentrations of Pb and Cu were higher in the AO-horizon than in the A0o-layer. Mobility of the elements decreased in the order Cd, Pb, Zn, Cu. (3) Pb and Cd concentrations in 0. cincta varied with site contamination, while Zn and Cu concentrations were more constant. The metal concentrations in Collembola were not clearly related to any particular chemical fraction of the soil metals. (4) Resistance of 0. cincta to Pb and Cd was studied by budget experiments and standardized assays of metal excretion. (5) Intestinal assimilation from dietary exposure was 0-4% for Pb and 8-3%/, for Cd. From the assimilated amount, 48% of Pb and 30% of Cd was excreted per moulting interval by intestinal exfoliation. (6) Although there was considerable interindividual variation, the average excretion efficiency was not influenced by physiological effects of such factors as degree of exposure, weight or sex. (7) Comparison of ten populations showed that high soil contamination in mining areas resulted in populations of 0. cincta having an increased average excretion efficiency for Pb and Cd.
