This is the paper that is used to justify the widespread use of avermectins. The abstract is publicly available.

They admit "Some species of the coprophagous insect fauna, particularly in the larval stages, can be adversely affected by the presence of avermectin residues in the faeces", but plead in mitigation:

1. Peak avermectin use and peak insect activity are often at different times of year in temperate agriculture. It’s not clear why it is better to kill them when they are less active (and the population is lower) than when they are more active, unless the suggestion is that the insects hibernate beyond reach of the avermectins.

2. Treatment is mainly of young animals which results in "the deposition on pasture of faeces which are predominantly free of avermectin residue." Dream on!

Finally they conclude: "Results of large scale, long term studies indicate that, even under conditions of relatively high levels of avermectin use in cattle, the impact on non-target insect populations and their function is limited." Not any more!

It’s clear that their idea of "relatively high levels of avermectin use" are far below the current levels.