Season-Long Simplification of Insect Communities in Dung From Cattle Treated With an Extended-Release Formulation of the Parasiticide Eprinomectin.

Cattle treated with LongRange®, an injectable formulation of the parasiticide eprinomectin, faecally excrete insecticidal residues for an extended period post-application. We examined the non-target effect of these residues by comparing insect communities developing in dung of untreated cattle (Week 0) to those developing in dung of cattle treated 1, 2, 4, 8, 12, 16, 20 and 24 or 25 weeks previously. Chemical analyses of dung showed that eprinomectin concentrations peaked at 1 week post-application and were still detectable at 25 weeks. Results from two separate experiments showed that dung of untreated cattle supported more total insects (beetles, flies, parasitoid wasps) and insect species than did dung of cattle treated ≤ 12 weeks (Experiment 1) and ≤ 25 weeks (Experiment 2) previously. For the two experiments, an effect of residue on individual taxa was either not detected (9 cases) or was determined to suppress insect development in dung of cattle treated 8-12 weeks (2 cases), 12-16 weeks (3 cases), 16-20 weeks (2 cases) or 24 or 25 weeks (6 cases) previously. Flies and their parasitoid wasps were particularly sensitive to residues with suppression often at or near 100%. These results show that cattle treated with LongRange® in spring will faecally excrete residues for the entire grazing season with an associated simplification of the dung insect community. The effect of this simplification on the long-term health on dung-breeding populations of insects on pastures and dung degradation was not examined in the current study, but merits future research. This article is protected by copyright. All rights reserved. Environ Toxicol Chem 2023;00:0-0. © 2023 SETAC.