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 cattle with a single standard injection of ivermectin (200 µg·kg-1) were 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 four herds were kept in four paddocks of about 80 ha. Dung insect communities were monitored before and for three months after treatment. A range of community measures, including univariate, graphical and multivariate methods, were used to assess the effects of ivermectin. The results suggest that the use of ivermectin affected community structure through reduction in species diversity and an increase in species dominance. These effects appear to have lasted for three months after ivermectin treatment when experiments were terminated.