Maggots-in-poultry-litter

Using larvicide to kill maggots before they hatch into flies can be effective © Olivia Cooper

Most people welcome the onset of summer, but for poultry producers it brings the threat of a fly population explosion. No matter how careful you are, flies will migrate and find their way into the sheds, and once they start breeding they can very quickly become a problem.

The most challenging sites are laying units with slatted floors, as the litter provides ideal conditions for flies to breed. So what can producers do to reduce the risk?

According to Dave Reece, fly consultant at Oakwood Farm Services and technical adviser to Lodi UK, the first step is to keep the farm clean and tidy to reduce potential food sources and breeding sites.

“Clean up feed spills and standing water, and make sure any dead bird bins are sealed,” he says. It’s impossible to keep adult flies out of a shed, given the need for ventilation, but pheromone traps outside the house can be effective.

See also: Keel bone damage in laying hens explored

The next step is to watch out for signs of fly activity as the warmer weather sets in. “Once you start seeing little muck flies that’s a definite precursor to a problem – look around the lights in particular.”

Depending on the season, flies can start to become in evidence any time between February and April.

Common flies

The main flies that are attracted to poultry units are common and lesser house flies, and it’s important to identify which ones are on site, he adds.

“People think that lesser house flies are the biggest problem but that’s not true: 90% of those I treat are common house flies, which are bigger and tend to sit around, whereas lesser house flies are smaller and hover in clouds.”

maggots around drinkers

Flies like warm, semi-moist conditions under drinkers © Olivia Cooper

Many producers aim to kill the adult flies with poisonous granules or paints, but limiting treatment to adult flies can cause serious problems, suggests Mr Reece.

This is because of the speed of the breeding cycle, as well as the increased risk of resistance to adulticide chemicals. “If you’re going to use an adulticide, then opt for a product with new active ingredients, not pyrethroids, because of resistance issues both in flies and red mite.”

The life cycle of a fly speeds up in warm weather. After hatching from the egg, there are three maggot stages before the fly emerges.

“In cooler temperatures it can take four weeks to get from egg to fly, but in hot temperatures that can drop to just seven days,” says Mr Reece.

“After hatching, the first thing a fly wants to do is breed; that’s more important than exploring the shed and eating fly bait. They can lay eggs within 48 hours of hatching, 100-150 eggs at a time, and can lay four or five times in their lifetime, which is why you can get such rapid population explosions.”

To combat the issue of a rapid breeding cycle and potential resistance to active ingredients in adulticides, it is vital to use a larvicide as well, says Mr Reece.

“There are no known resistance issues to larvicides, and using them reduces the pressure on adult products.” He recommends using a larvicide with cyromazine as its active ingredient, alongside an adulticide with azamethiphos in it.

Checklist

  • Monitor fly activity throughout the spring and summer season
  • Keep records of fly populations and treatments for 12 months
  • Act quickly once small muck flies are in evidence
  • Identify the fly species
  • Treat muck with a larvicide and use granules or paint to kill adults
  • Check for possible resistance against active ingredients
  • Work back from cleanout date and treat roughly every eight weeks
  • Use fly paper or tape in egg room, with pheromone traps outside the house
  • Treat dead bins against bluebottles
  • Fumigate sheds at turnaround to kill adult flies before next flock

“When I get called out to a farm, I identify the fly species first, and then apply a larvicide to the muck using a metered sprayer at 250g/10sq m.

“I’ll also lay out boards with adulticide granules or paint – although it’s important not to locate them near the egg boxes as the flies are attracted by the pheromones and will cause egg spotting.”

Typically, he will re-treat in about eight weeks, but it will depend on the fly pressure.

“It’s absolutely essential to keep monitoring the shed,” says Mr Reece.

“You can use sticky tape to catch them or spot cards to indicate where flies have vomited their food to digest it – and you need to keep them for 12 months alongside other records to demonstrate what action you’ve taken.”

Flies cost

The cost of failing to control flies can be considerable. “It carries up to a £10,000 fine and six months in prison under the Clean Neighbourhoods Act,” he warns.

As well as reducing the risk of public complaints against fly nuisance, controlling flies on the farm will also decrease the risk of disease.

“Producers have a duty to control flies; they carry hundreds of diseases and if you have a disease you don’t want to pass it onto a neighbouring farm.” In addition, fly spots on eggs can often result in them being downgraded to seconds.

Flies like warm, semi-moist conditions for breeding, so poultry litter is ideal, especially under drinkers or where there has been a water leak, says Mr Reece.

“The maggots of common and lesser house flies are very different, so take a sample of muck and look through it – you could also put it into water which separates the muck and the maggots.” Spot treating wet areas is a good way to prevent possible problems getting out of hand, as is, of course, fixing any leaks.

At cleanout, the muck is usually spread on nearby farmland, which can again lead to a problem with flies, he adds.

“You could treat it before it leaves the site, but there may be a withdrawal period before you can spread, so it’s best work back from your turnaround date; treat two months before cleanout and eight weeks before that.”

Of course, fumigating the shed to kill any adult flies before bringing in the new flock is also essential. “If you leave any adult flies around they will be straight into the new flock.”

The treatment for adult flies and larvae will depend on the breed of fly, explains Mr Reece. “In maggot form the treatment for lesser and common house flies is exactly the same, but once in adult form it’s about locating the adulticide correctly as they contain pheromones to attract the flies to the bait.”

The active ingredient azamethiphos is effective on both species, but while common house flies are strongly attracted to the bait, lesser house flies are less so, so it’s important to place the boards where the flies will rest.

Bait boards

“I like to use granules as they disappear as they’re being eaten, so it’s easy to see when they need replacing,” says Mr Reece. “However, the paint products will last a bit longer – but don’t just paint the shed walls – it’s best to use boards that you can remove.

I’d recommend 10-15 A3-size boards per 12,000 bird shed.” For lesser house flies, put them on the wall and roof, and for common house flies hang them below the slats – that way you can paint both sides.

“The closer you put it to the fly the quicker you’re going to get control.” To combat bluebottles, which are meat eaters, producers can sprinkle S-methoprene into the dead bins, he adds.

“A typical larvicide treatment will cost around 2.9p/bird including labour – if you’re doing it yourself it will be about 1.4p/bird, but you need to be sure of a professional job using effective products,” explains Mr Reece. “Larvicide treatments are more expensive but in the long run you really will save.”

Other options include hanging flypapers in the windows of the egg packing room, using ultraviolet traps, or stringing up fly tape.

“However, UV traps are only effective against common house flies, not lesser house flies,” he warns. Parasitic wasps can be another, non-chemical alternative, but do require forward planning as they won’t cope with a population explosion.