Some effects of ivermectin on the yellow dung fly, Scatophaga stercoraria

Ivermectin was added to fresh cattle dung at a range of concentrations based on those found in faeces of livestock treated by injection. Newly hatched larvae of Scatophaga stercoraria were then reared in the dung as a bioassay. The EC50 values for 24 h and 48 h larval mortalities were 0.051 ppm and 0.036 ppm (wet wt.) respectively. When the dung concentration was 0.015 ppm, 50% of the insects failed to pupariate and a level of 0.001 ppm prevented adult emergence in 50% of the insects. When batches of larvae were reared in dung containing as little as 0.0005 ppm, the emerging adults showed developmental abnormalities in wing morphology. In addition to the significantly higher level of fluctuating asymmetry, 23% of the treated insects developed new veins and new cells in the wings. The observations are discussed in relation to previous work and attention is drawn to the practice of failing to observe the full impact of sublethal effects, which can be as serious as those of acute toxicity.