A method of evaluating the adult fly population in and around an animal production facility is needed to design and evaluate a fly control program.

Systematic monitoring provides a measure of the success or failure of control methods, and serves as an early warning system so that changes can be initiated before a crisis develops.

Monitoring also provides the information needed to time adulticide applications.

Larvae monitoring provides the information needed to use larvicides, and for making changes in cultural practices.

Casual, subjective observations on fly numbers can be misleading and systematic monitoring is more objective and reliable.

Lawsuits sometimes arise in connection with flies alleged to come from animal production facilities, and quantitative data from systematic fly monitoring can become important.

Monitoring is a key component of an integrated fly control program.

Different ways of monitoring populations of adult flies include: fly grids, resting counts, sticky fly ribbons, baited jugtraps and spot cards.

These methods are directed primarily at obtaining a measure of the numbers of house flies, the principal pest. Different methods have different capacities to reveal which species of flies are present.

 

 

Fly Grids & Resting Counts

Fly grids are wooden squares made up of many slats measuring about a centimetre.

The grid is placed on the floor and the number of flies resting on the grid counted at various time periods.

This sampling device was originally developed for use in restaurants and mess halls, and its usefulness in animal facilities is limited. The time-of-day placement causes great variation in the results and, of course, the observer has to be present. The species of flies can only be identified from a quick glance by the observer.

Resting counts are sometimes used in animal facilities. Predesignated areas of partitions, portions of feed troughs, posts, railings, ceilings, etc., are chosen and the number of flies resting in those areas counted.

House flies resting on a ceiling. Notice spotting left by the flies and their preference for resting on pipes along the edges of cracks. 

Several areas are used in each facility. Also, the number of flies resting on the animals or portions of the animals (especially with swine and calves) may be counted.

With several areas or animals being examined, fairly reliable data can be obtained. However, the same limitations as with fly grids apply in that the observer has to be present, counts are for only a brief period and fly species cannot be accurately determined.

 

 

Fly Ribbons

Sticky fly ribbons are commercially available and the flies caught on them give a useful index of fly population.

Fly ribbons also allow the species of flies stuck on the ribbons to be positively identified.

Several ribbons are placed in a facility. The positions in which the ribbons are placed and the number used are important variables.

The ribbons should be replaced in the same locations in order to be able to compare fly counts from sample to sample.

Usually the ribbons are left in place for a few days, but if left for more than 3 days or if there is a large population of flies, the ribbons will become filled with flies and the rate of catch will decrease drastically.

In dusty situations, especially in poultry houses, the dust will render the ribbons ineffective in a day or two.

Sticky ribbons are messy to handle but offer the advantages of being able to identify the fly species and providing a sample of flies over a period of a few days.

 

 

Baited Jug Traps

Baited jug-traps are a simple, practical fly monitoring device and can be left in place for up to one week to give a continuous sampling of flies.

The same trap can also be used for the purpose of fly control.

The baited jug-trap consists of a 4 litre plastic milk jug with four holes (7.5 cm diameter), cut around the circumference in the upper third of the jug.

About one tablespoon of fly bait containing muscalure is placed in the bottom.

Flies enter, feed on the bait and die in the jug. The number of flies and the species caught can be determined easily.

After one week the bait has reduced effectiveness, so the flies and old bait should be dumped and the bait replaced.

The placement of traps is important: they should be in the same locations week to week, throughout a monitoring period.

The number of traps needed depends upon the precision desired and the level of fly numbers to be detected.
 

At least six traps should be used per facility.
 

In poultry houses, an index of 350 flies per trap per week has been used as the threshold for chemical treatment.

 

 

Spot Cards

Spot cards are simple devices for measuring fly activity when lower thresholds are desired, such as when neighbors are close or animal facilities are open to visitors (for example, horse stables).

Spot cards are white 7.5 x 10cm file cards which are fastened flush to pre-chosen locations in a facility.

They are fastened to posts, rafters, partitions, feed troughs, etc., where the animals will not disturb or soil them.

Flies resting on the spot cards leave light straw-colored regurgitation spots and dark fecal spots. The number of spots per card is easy to count after an exposure period of about 3–7 days.

Exposure for longer than 7 days is not practical because the cards become too soiled.

Cards may be labelled, counted, and kept for later reference if needed (such as in legal proceedings relating to fly complaints).

Most spots are caused by the house fly. However, if other flies are present (especially Ophyra spp.), they will spot the cards. Therefore, spot card counts are only an index of fly activity. The species of flies cannot be determined from spot card counts.

Other observations should be made to verify whether or not the house fly is the most abundant species.

The placement of spot cards (like ribbons and jug-traps) is important, and they must be placed where flies are observed to rest or where fly specks are present.

Generally, locations in higher areas, as high as a person can reach, are desirable.

Several cards are necessary depending upon the level of fly activity to be measured, and the precision desired.

At least 10 cards should be used in a facility.

In poultry houses, an index of 50 spots per card per week has been used as a threshold for chemical treatments.

In different situations, lower thresholds may be chosen.

 

 

Larvae & Pupae

Monitoring for fly larvae and pupae is important in determining specifically where flies are developing (breeding), and in order to use cultural and chemical control (larvicides) effectively.

Locating fly larvae is laborious but it must be done in order to know what changes in manure handling and facilities maintenance may be needed to reduce fly breeding.

It is also necessary in order to know precisely where to apply larvicides.

The only practical way to monitor for fly larvae is to examine likely places and remove portions of manure, silage, bedding, etc., for closer examination. The large third-instar larvae and brown pupal cases can be seen easily.

All possible breeding habitats should be inspected. Particular attention should be paid to manure accumulations in places that are difficult to clean, as well as spilled feed, silage, feed bunkers, around waterers, hay racks, under margins of hay bales, etc.

Once the fly breeding spots (where fly larvae are seen) are detected in a facility, they can be given special attention during routine monitoring.

Breeding sites can also be larvicided at the time of monitoring, if necessary.

Since the life cycle of the house fly and many other species is only about 7–10 days in hot summer weather, monitoring should be at least once a week and preferably twice a week.

This can be integrated with a systematic overall inspection of the facilities and animals, to detect any animal health or equipment problems.

Such routine inspection is a sign of good herd and flock management.