The problems caused by apparent overabundance of cow faeces (Turd world: how poo is mucking up the environment, 25 March) are at least partly in the control of the farmers, who feed a broadband insecticide (Dimilin) to their cows.
The purpose is to stop flies and beetles from feeding in the dung and thus breaking it down, a crucial step in the removal of the dung. Flies and beetles are thus no more a problem in intensive rearing units. Dimilin can remain active in the dung for a month or more, so when the dung is disposed of, it is still not possible for an insect (or many other species of arthropod) to survive or breed in it. Dimilin then becomes an added pollutant of run-off and water courses.
Its action is to disrupt the formation of a primary component (chitin) of the insect’s skin or shell. So the shell is never formed properly and breaks very easily, usually when the insect is expanding into its new shell after moulting. It can also affect the insect’s gut lining. I did some of the early work on Dimilin.