Animal indicators for side-effects of chemical vector control.

In many places in the tropics pesticides are applied in the natural environment to control insects either for crop protection, or for human health. The present study concerns the side-effects of insecticides that are applied in West Africa against tsetseflies (Glossina spp), which are the vectors of human and animal sleeping sickness. Pyrethroids and endosulfan were sprayed either by helicopter or by ground spraying on riverine forests and on forests around villages.Because of the complexity of the terrestrial and aquatic ecosystems under study, a selection was made of populations in which side-effects were assessed (so-called indicators). Fish and benthic arthropods were studied in the rivers; Diptera, Hymenoptera and spiders in the forest. Observations on short-term effects revealed the most vulnerable populations (indicators for effects) depending on the insecticide and the method of application. Long-term studies, up to two years, revealed the differences amongst these populations in ability to recover from local depletion. The populations which recovered most slowly were regarded as indicators for recovery.Differences in hydrological regime between climatic zones are regarded to be highly related to differences in vulnerability of ecosystems to irreversible damage by pesticides.