When springtime arrives the earth is warmed up and it bounds back to life. Most of that life is very welcome, but some of it we would rather do without. One such example we equine lovers have to deal with are those pesky flies. Why do horses and flies go hand in hand anyway? The answer is because the horses provide flies with an abundance of their favourite breeding ground: manure. If we can limit fly population where they breed by introducing natural enemies, then it becomes a long-term solution without any harmful side effects.

Fly life-cycle
Adult filth flies deposit eggs in organic matter, such as manure and wet feed. This is an excellent food source for maggots that hatch from the eggs. As it goes through its development, each larva (maggot) eventually transforms to the non-feeding pupal stage. During this time it forms an armor-like coating, which is developed from the larval skin and protects the pupa during its metamorphosis to an adult fly. Finally the adult fly emerges from the pupa, and can then repeat the life cycle.

Why are Flies So Hard to Control?
When we talk about flies as pests, what we are really referring to is the adult stage of the fly – the stage that annoys and harms by spreading disease among horses through tainted blood and/or mucus. Therefore, traditionally most of the focus was on controlling this adult stage, usually with pesticides. The problem with this approach is that it is only a band-aid solution – you may kill the adult flies but there are three other stages developing at the same time; egg, larva, and pupa. Once they reach maturity you have the same problem all over again, and it doesn’t end until the temperatures are too cold for insect activity. Without any control measure during warm weather fly populations can become unbearable.

How to Control Flies?
Gone are the days of using strictly pesticides for pest control. Industry experts, government officials and scientists all agree: IPM brings the best results. IPM stands for Integrated Pest Management – a system of using all of the techniques available for pest control. The techniques used are Biological, Cultural, Mechanical, and Chemical. They all have their effectiveness but work best synergistically.

Cultural, Mechanical, & Chemical Control
Cultural methods are generally related to sanitation – the cleaner your stables the less flies you will have. Stalls should be cleaned daily, and the manure piled away from any buildings. Bedding should be changed and refreshed regularly and stalls let to air-dry occasionally. Stalls should also be thoroughly cleaned and disinfected seasonally. Finally, the manure pile should also be removed regularly. Mechanical methods are physical devices like sticky rolls and string, and solar fly traps. They are non-toxic and help reduce adult fly populations. These products can be found at your local co-op or hardware store. Chemical methods bring a fast reduction of adult flies but do nothing to combat the immature stages. They bring quick relief but do not provide a good long-term solution. Also, there are many harmful side-effects with chemical use:
• Pesticide resistance, where pesticides lose their effectiveness.
• Harmful effect on non-target species. Many times beneficial organisms are harmed.
• Environmental (nature) contamination. Soil degradation and water table pollution.
• Worker (applicator) safety.
• Owner, handler and animal environment.
Still, chemicals can be part of an effective program as long as they are not relied on too heavily. Products such as fly bait, a granular substance impregnated with a synthetic pheromone (attractant) and pesticide can help keep populations low and are not as bad as spraying structures.

Biological Control
This method introduces natural enemies of pests that instinctively prey upon or parasitize them. 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 by having 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.