CHANGES IN THE STRUCTURE OF DUNG INSECT COMMUNITIES AFTER IVERMECTIN USAGE IN A GRASSLAND ECOSYSTEM - I - IMPACT OF IVERMECTIN UNDER DROUGHT CONDITIONS

Changes in structure of dung insect communities after treatment of cat tle with a single standard injection of ivermectin (200 mu g.kg(-1)) w ere investigated in a large-scale field study under extensive farming conditions in South Africa. The study was carried out during a period of drought. Two herds of cattle were treated with ivermectin, whereas a further two herds remained untreated and served as controls. The fou r herds were kept in four paddocks of about 80 ha. Dung insect communi ties were monitored before and for three months after treatment. A ran ge of community measures, including univariate, graphical and multivar iate methods, were used to assess the effects of ivermectin. The resul ts suggest that the use of ivermectin affected community structure thr ough reduction in species diversity and an increase in species dominan ce. These effects appear to have lasted for three months after ivermec tin treatment when experiments were terminated. (C) Elsevier, Paris.