Flies are very difficult to control because traditional methods only focus on the adult stage. This may bring a sudden “knock-down” effect, but it is normally short lived and soon after you have the same problem.

Biological control introduces natural enemies of flies that instinctively prey upon or parasitize them in their immature stages. The industry is heavily regulated, and any commercial products must be indigenous and not harmful to any other non-target organisms before being made available. For flies, insects known as “fly parasites” are now commercially available and being successfully used. When fly parasites are released where flies breed (manure), they instinctively find and parasitize the fly pupa, injecting an egg inside it. The egg soon hatches into a fly parasite larva, and it consumes and grows inside the fly pupa, eventually killing it before completing its own life-cycle and emerging as an adult fly parasite. So now you have killed the fly before it has even had a chance to become a pest! That is the beauty of using natural enemies such as fly parasites.

There are two keys to the successful use of fly parasites: start early before you have fly problems, and introduce them regularly throughout the year. This is because the fly has two major reproductive advantages over the fly parasite: its egg laying capacity is ten times that of the fly parasites, and its development time (from egg to adult) takes only half the time. This means that one generation of flies is much greater than one generation of fly parasites. Therefore you must start early and never give the flies a chance to get the upper hand – do this with regular introductions.

The fly parasites are mixed with wood shavings and are sold in ‘colonies’ of 10,000 per bag. The bags are simply released in horse stalls, manure piles, and other areas where manure and decaying organic matter is found. They are completely safe for both human and animal health, and are economical and easy to use. The amount that you need depends on the number of horses that you have – the more horses, the more manure, the more flies, the more fly parasites needed. The main thing to remember is to start the program early, before you have serious fly problems. More information on fly parasites can be found by contacting Bugs For Bugs, in Guelph, Ontario, at 1-866-577-1117, frank@bugsforbugs.ca, or www.bugsforbugs.ca.

A fly parasite parasitising (and thereby killing) a fly pupa

The fly life-cycle interrupted by the fly parasite