Thus, four weeks of collections generated 20 pairwise comparisons. When data was lost for one member of a pair, that pair was excluded from analyses. For Experiment 2, weekly catches from traps baited with dung from untreated cattle, or from cattle treated 1 wk or 4 wk previously, were analysed using Kruskal-Wallis tests. Many species were not collected for periods of several weeks or months because of seasonal variation in adult activity. Changing the order of baits in the latter experiment did not alter this result.
Ivermectin therapy can alter insect colonization of dung from treated cattle.
However, the nature of this effect can vary. Whereas Experiment 1 showed ivermectin therapy to enhance colonization, Experiments 2 and 3 showed ivermectin therapy to suppress colonization. These conflicting results may reflect a change in cattle diet. Cattle in Experiment 1 were fed alfalfa cubes, and cattle in Experiment 2 and in Experiment 3 were fed barley silage. Differences in diet can affect levels of ivermectin residues in dung, which may have altered the preference of beetles for dung from treated cattle.