The creation of resistant strains in the field can be countered by using insecticides according to resistant management strategies.
Three basic strategies have been developed and refined (Georghiou, 1994):
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MODERATION
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SATURATION
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MULTIPLE ATTACK
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Intermittent use of short-lived products.
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Thorough treatment that eliminates the insects.
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Combined use of widely different products.
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These concepts can be, and are in many cases, combined. For example, the Multiple Attack may be used in the Moderation and Saturation concepts.
A Saturation area on a single farm can be protected (with fly screens on the windows and ventilation units, doors with curtains etc.) from a wider Moderation area.
Climate, reinfestation pressure, manure management practices etc. also play a part in the choice of the correct strategy.
The aim is always:
to avoid strong selection of consecutive generations of a fly population with a single insecticide.
“Population” is a key word in this statement.
In some areas a single fly population will stretch over a whole neighbourhood. A local saturation strategy may turn out to be a Moderation strategy when the true extent of the fly population is discovered.
Untreated insects within the population dilute the selection pressure. “Refugia” are deliberately left or created as a source of susceptible insects in cropping systems. This should be considered in fly control, on a case-by-case basis.
In other areas the whole fly population will be within a single building, and in some systems it is possible to eliminate the whole fly population, e.g. when all animals are removed in the winter and the building is disinfected. This “saturation” treatment eliminates selection pressure as well.
Advances in biochemistry, molecular genetics (Hemingway & Ranson, 2000), ecology, population dynamics, monitoring etc. have made the house fly resistance problem less alarming in recent years. Workable solutions have been developed in many situations.
However, strategies continue to be developed further, and local recommendations still need to be periodically updated with state-of-the-art information.
