This concept entails the acceptance of “nuisance thresholds”.
In many systems we can accept the presence of a certain number of flies. There are many beneficial organisms keeping fly populations lower than they would otherwise be.
However, at certain times of the year fly numbers are no longer tolerable and short-lived products can be used.
Granular baits, spread where flies congregate, are exposed to daily farm activities and functionally short-lived.
Paint-on baits present a depot of attractive material which is actively imbibed by the insects. A concentration can be chosen to minimise the possibility of selection at sublethal doses. Flies that find the depot are killed and the others are not selected. This again follows the concept of moderation.
Baits have little direct effect on beneficial organisms, as they are carefully placed for maximum effect on the adult flies.
It is also possible to target key breeding sites, using a narrow-spectrum larvicide on “hot spots” at the start of the season (or as needed).
Natural biological control agents have a good chance of survival in this system. In fact, larvae surviving a “hot spot” treatment (and possibly carrying genes for resistance) may either be eliminated by (hungry!) parasites and predators, or mate with incoming adults which have not been exposed to the larvicide.
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