If knockdown chemicals are effective you can continue to use these away from the
manure. Do not use them in the pit or through the slats as you will kill your valuable
wasp population.
Paint on fly attractants are effective and when hung in the house will not affect
the wasps at manure level.
Pheromone traps are also very effective in large enough quantities.
All attempts must be made to reduce the ingress of flies from the outside, other
farm animals or buildings with old manure. The fly life cycle is slightly shorter
than the wasp and as with any biological control there has to be some food for the
wasps to survive, but not too much.