STABLE flies have reached critical numbers and are causing civil unrest in the central American nation of Costa Rica.
The escalation of the pest numbers in some regions of the world has highlighted the threat to livestock farmers and residents across 14 local government areas along the coastal plains of WA, if the problem with the fly is not brought under control quickly.
The Stable Fly Action Group, in partnership with the Department of Primary Industries and Regional Development (DPIRD), held a stable fly symposium in Gingin recently to inform local cattle and vegetable, producers, as well as affected industry personnel, of the research conducted to date on the fly and measures that can be taken to minimise, and if possible, eradicate it before the situation gets worse.
Local cattle producers expressed cautious optimism that efforts to minimise the stable fly would be successful in coming years if everyone worked together to achieve the desired outcome.
However, the issue of rogue producers who flouted the laws and failed to comply with the State regulations for vegetable product waste and poultry manure, were of most concern because of the risk of establishing the stable fly in areas where it is not a major problem.
Research from the United States, Costa Rica, Brazil, and WA was presented at the symposium by the world’s leading scientist on the stable fly – US Department of Agriculture senior research entomologist David Taylor from Lincoln, Nebraska.
Dr Taylor said stable fly was “the most frustrating insect” he had ever worked with because just when he thought he knew something about its habits and patterns, new information would throw everything back up in the air.
“What I have learned is that there are three ways to deal with the stable fly – sanitation, sanitation, sanitation,” Dr Taylor said.
“The problem is farmers don’t know how to identify it from other flies.”
The flies breed in feedlots where manure is mixed with straw and is left for too long, or after vegetable or fruit harvest among residue waste.
The male and female stable fly are blood feeders that need to eat once or twice a day, every day.
They tend to feed on the lower legs and body of cattle and can take from two to four minutes to complete a meal.
Dr Taylor said research showed that the fly had the potential to travel up to 200 kilometres (in Florida – due to the lack of livestock in the area).
The median distance is 1.6km.
“They go as far as they have to go to find blood,” Dr Taylor said.
“It is quite possible that they can travel 30km in 24 hours.”
Dr Taylor said there was “a long list of things that have been implemented as possible mechanical vectors, but there has been no proof of any disease recorded to date”.
He said numbers as high as 27,000 stable flies per square metre have been recorded.
“In the US 15/m2 is the economic threshold,” Dr Taylor said.
He said 30-50/m2 was a serious outbreak and above that was terrible.
“It will drop animal productivity to zero and increase the mortality rate of livestock,” Dr Taylor said.
He said Costa Ricans were experiencing 20 million stable flies per hectare – which was directly related to the increase in production of the pineapple crop, which created mass amounts of waste after harvest.
“In Costa Rica it’s causing social unrest,” he said.
“It is the most serious problem in that country.”
Dr Taylor said the secretaries of agriculture of the US and Costa Rica were meeting to discuss the issue – which highlighted how serious it had become.
Costa Rica supplies the US with all of its pineapple imports and it exported three million tonnes per year from 45,000ha of plantations.
Brazil was seeing an increase in the fly due to its sugar cane industry production waste.
Dr Taylor said the only way to control fly numbers was to “change our culture” because they lived and bred in on-farm waste.
“Different cultural practices affect volumes of numbers in different areas,” he said.
“We are trying to put together an international group of researchers to develop the issues.”
DPIRD research entomologist David Cook, a member of the new group, has been doing on-farm trials in WA with mulching vegetable waste and compacting the soil at varying depths to test the strength of newly-hatched stable flies as they emerge from the pupae.
Mr Cook said compaction of the coarse sandy soils found in WA’s vegetable growing regions would be 95 per cent successful in eradicating stable fly.
He said there was a two step process where farmers buried their crop residue using a mouldboard plough up to 45 centimetres deep, a stone burier to 30cm deep, or a deep slow rotary hoe to 30cm deep – then compacted the soil.
Mr Cook said the benefits were three-fold – farmers would minimise soil and moisture loss and prevent the outbreak of stable fly.
An adult fly has the capacity to burrow its way through the soil to the surface unless the soil is compacted to 5cm or more.
Continued funding for more research and trials was cited as an essential element of understanding and fighting back against the pest.
DPIRD representative Don Telfer said he was unsure about the future of the stable fly project in WA when funding runs out in April 2018.
