‘Look beyond chemicals’ says ADAS fly expert

Using chemicals to control fly problems should be a last resort, producers were told by ADAS pest control manager Barbara Bell at a meeting in the south west. And alternative control methods would become ever more important as products continued to be removed from the shelf.

Ms Bell said that the loss of Alfacron this year—as a result of the noose tightening around organo-phosphates—was a major blow and comes on top of the withdrawal from sale last year of Golden Malrin.

"We've effectively lost the two best products there were for killing adult flies," said Ms Bell, addressing the NFU/BFREPA free range meeting in Exeter.

Producers need to adopt an integrated approach to fly control, she said. This included correct design of buildings, effective management and systematic monitoring of fly populations. Chemical treatment was the last line of defence.

"You can't make a free range house fly proof," said Ms Bell, "but you can think about the design, particularly with water in mind.

"Make sure roof water is piped away correctly and not allowed to mix with dust and dirt outside the unit. The resulting sludge will prove most attractive to any flies in the vicinity."

And keeping water out of the house is essential if the dung pit is not to become a fly breeding haven. House flies—which are the main problem on poultry units—favour muck with a moisture content of 40 - 70%.

In normal conditions it is 70 - 80% when it leaves the bird but this can be higher in warm weather with the birds drinking more. Incorrect diet formulation can also lead to excess water intake, leading to wetter droppings.

With a female housefly able to lay 100 eggs in a week, and an adult fly developing from the egg also within a week, it is essential that reproduction is curtailed.

"If you can get the moisture content down below 40%, although the flies will still breed, the larvae will not hatch," said Ms Bell.

"Good air movement in conjunction with effective drainage outside the shed, and no leaking or slopping drinkers inside, will help you achieve this target.

"Dry manure will also encourage beetle activity, and the species Carcinops is particularly effective at predating on fly larvae."

Although there are two other species of fly that can be found around poultry units they are unlikely to be a major problem. Blowflies are easily avoided by maintaining good hygiene standards, for they will only be found where there are carcasses left hanging about. The other type, dung flies, are usually only present for a short period after restocking and can be controlled with a knock-down spray. But Ms Bell had two pieces of advice when it came to knock-down insecticides. Firstly, don't use them over the pit because they will kill any beetles and, secondly, use them sparingly—no more than weekly—because resistance to them can build very quickly. And producers can check the effectiveness of the spray themselves by collecting up some of the 'dead' flies and putting them in a plastic bag.

"Have a look at the bag an hour later and see how many are flying around," said Ms Bell. "It's these flies that are left to breed another day that will continue adding to the resistant population."

Systematic population monitoring is the cornerstone of any control measure, producers were told, and if they did not keep an eye on fly numbers they could expect to be caught out. Monitoring numbers allows treatments to be timed to best effect, leading to reduced use of insecticides. It also demonstrates due diligence, vital should you get a visit from environmental health officers.

Fly populations can be monitored quite simply by marking 1 metre squares around the building, such as on walls, and counting the number of flies. The exercise should be carried out at the same time of day, once a week in the winter and twice a week in the summer.

"You'll be able to spot a problem developing and take appropriate action," said Ms Bell. "Record everything meticulously, including any treatments, and you will have a good defence should you ever find yourself under the spotlight of the local authority."

But if the ADAS entomologist had one piece of take-home advice for producers, it was for them to insist that EHOs have any flies at the centre of a complaint properly identified.

"Poultry farms are an easy target when a fly nuisance is reported," said Ms Bell, "but the flies being complained about may not always originate from the unit. Expert identification could stop an investigation of your premises dead in its tracks."

The biological approach

For organic producer Georg van den Berg using chemicals to control flies is not an option, and his unit on the outskirts of Crewkerne in Somerset has already been visited by the local authority following a complaint.

While Georg managed to convince the EHO that he was doing all he could to control the flies—using large sticky papers and encouraging beetles—and the matter has not been pursued further, he is concerned that he risks being targeted in the future.

"Being organic means we have very few options open to us, and yet with people living quite close to the unit I'm sure someone will point the finger at us again," said Georg, who is now considering biological control methods.

With a background in horticulture, biological pest control is nothing new to Georg and he's been investigating whether the concept can be put to use on his unit.

Currently in the UK natural predation of flies in poultry houses is based on indigenous species, such as the Carcinops beetle. But elsewhere in Europe—and in America—poultry farmers are using specially bred wasps and predator flies as a control method.

In dry manure a range of parasitic wasps—Nasonia, Spalangia and Muscidifurax—will thrive and feed on fly larvae and Georg, having been given clearance by Defra, is aiming to import the wasps from Germany in time for next spring when fly numbers start to build.

The wasps' life cycle involves laying eggs inside the larvae of the pest fly. When these eggs hatch the resulting wasp larvae feed on the host fly larvae, and around eight adult wasps should then emerge to begin a new cycle.

"The idea is to release fly larvae carrying the wasps' eggs into the pit at the beginning of the season and then every fortnight throughout the summer," explained Georg. "Up to four weeks after release the wasps will hatch."

And producers need not be concerned that they may get rid of the flies only to be plagued by wasps, for Georg told the Ranger that the wasps are only 2 mm in size and will not normally be seen after release.

Where producers have a problem with wet manure—and keeping pits dry is not always easy—Georg has discovered that biological control is possible using the predatory fly Ophyra aenescens, which feeds on fly larvae. Under normal circumstances, and if left undisturbed, the predatory flies will not leave the warm, wet manure and a balance between their numbers and the pest fly will be established after around eight weeks.

Georg says both the wasp and predatory fly will co-exist happily with any beetles that are already living in the manure, but because the wasps will predate on the Ophyra fly they cannot be used together.

Georg estimates that the cost of the wasps or predatory flies will be in the region of £1 per sq metre of manure surface, providing there is sufficient interest from producers to make the project viable.

"I know that biological approach to fly control is being used successfully elsewhere in Europe and I'm confident it can work over here," said Georg.

If you are interested in trying either the wasps or predatory flies—or simply want to learn more—Georg can be contacted on 07977 206530 or email Georg@weedmachine.co.uk