An important biological control, and benficial landscape insect is the fly parasites. They are generaly small parasitic wasps that attack and kill filth flies in their immature pupal stage. Highly effective because they kill the pest before it can mature into a flying adult. Female parasites deposit their eggs inside the pest pupae and once hatched, the tiny fly parasite larvae consumes the contents. Fly parasites can be very aggressive and have a strong natural incentive to actively seek out fly pupae in order to reproduce. They will not bother humans or animals
Fly parasites are shipped still developing inside the host, packed in a paper bag, and mixed with wood shavings for protection. Depending on the temperature during shipment, parasites will start hatching 1-4 days after arrival. Warmer temperatures will make them hatch faster, while cooler temperatures will slow the hatch. Do not store at temperatures lower than 60° Fahrenheit.
Start releases when some parasites have hatched in the bag. Keep the closed bag in a warm place (around 70° F.) out of the sun until you notice some movement inside. Release fly parasites as close as possible to the breeding sites where fly larvae activity can be seen or is suspected. Do not release them all in one spot and try to cover the entire fly breeding area. Parasites will move around in a 100 yard radius in search of pest pupae and will even burrow into the breeding site. Simply sprinkle the parasites out of the bag. If direct sun is a problem, covering the pupae with dirt or organic matter is advised.
For best results, start releasing before flies become a problem. Release rates, as with any beneficial insect, depend on several factors. The following guidelines have been successfully tested under normal pest conditions:
large animals (horse, cow, etc.) - 500 per animal
medium animals (sheep, goat, etc.) - 250 per animal
small animals (birds, rabbits, etc.) - 5 per animal
manure & compost piles - 5 per cubic foot
Note: These parasites do not attack adult flies, thus care must be taken to keep the existing population as low as possible. We recommend using at least one fly trap and perhaps even baits. If a quick-knockdown is required, avoid spraying near the breeding sites where beneficial insects are active. It will do more harm than good.
Along with beneficial insects, you should employ a combination of measures to achieve the greatest reduction of flies: cultural control (sanitation), manure management (disposal), and water management (fly larvae need a moist environment to grow).