Endectocide residues affect insect attraction to dung from treated cattle: implications for toxicity tests

Area of Science:

• Veterinary Entomology
• Environmental Toxicology
• Insect Ecology

Background:

• Endectocides are widely used in cattle, and their residues can enter the environment via dung.
• Assessing the impact of these residues on dung-colonizing insects is crucial for understanding environmental effects.

Purpose of the Study:

• To evaluate the effect of topical endectocide residues (doramectin, eprinomectin, ivermectin, moxidectin) on insect attraction to cattle dung.
• To determine the duration of these effects and their implications for residue toxicity assessments.

Main Methods:

• A 3-year field study in southern Alberta, Canada, comparing insect captures in pitfall traps.
• Traps were baited with dung from untreated cattle versus cattle treated 7 days prior with specific endectocides.
• Further experiments in year 3 assessed dung from cattle treated 3, 7, or 14 days prior with doramectin.

Main Results:

• Endectocide residues significantly affected insect captures for 27 taxa, with effects observed in both spring and autumn.
• Doramectin showed both attraction and repellency, eprinomectin tended to repel, while ivermectin and moxidectin strongly attracted insects.
• Doramectin residues applied 14 days prior still affected insect captures, with residues enhancing attraction in several cases.

Conclusions:

• Endectocide residues demonstrably alter the attractiveness of cattle dung to colonizing insects.
• Insect activity in dung pats is a composite measure influenced by residue toxicity, insect community composition, and other mortality factors.
• The emergence of insects from dung should not solely represent residue toxicity but rather a broader 'insect activity' metric.