With their big, bulging eyes, buzzing wings and extreme capacity for causing annoyance, house flies are, for better or worse, familiar to us all.
In fact, it is said that more than nine out of 10 flies found around people belong to the house fly species, which has the Latin name Musca domestica.
Although it can be irritating to have them whizzing around us, house flies can cause far greater problems than a few frayed tempers, because they also spread diseases that affect both people and farm animals.
As many as 65 pathogens have been found to be transmitted by house flies, including a number that cause intestinal diseases.
It is no wonder then that farmers commonly turn to insecticides to eliminate these tiny but often harmful creatures.
A new study by Dr Mohammad Al Deeb, a UAE University associate professor of entomology, has indicated, however, that many of the house flies here carry forms of genes that make them resistant to a commonly used group of insecticides, the pyrethroids. In one part of the country, 70 per cent of flies tested carried two copies of an allele, or form of a gene, that conferred resistance.
Published recently in the journal Agricultural Sciences, the paper is believed to be the first to look at the presence of insecticide-resistance genes in UAE insect populations. It could, hopes Dr Al Deeb, lead to more attention being given to ways to prevent resistance developing in pest populations in the Emirates.
“Here, we know how to control the insects by buying traps and using chemicals but no one is keeping an eye on what’s happening at the genetic level,” he said.
“I hope this paper will be the starting point for ... an insect resistance-management programme in the UAE.”
Resistance among house flies to pyrethroids and other insecticides has been well documented in other parts of the world, with a 2011 paper in the International Journal of Biological Sciences saying the creatures “have shown remarkable abilities to develop resistance to the insecticides used against them”.
An additional problem with insecticides is that they typically kill off susceptible insects but allow those with resistance alleles to live on and breed, so these alleles become more prevalent in the population in later generations.
In a similar way, concerns are often expressed about the way that antibiotics favour resistant types of bacteria, and for this reason doctors are counselled against using them excessively.
Dr Al Deeb caught house flies in five emirates — Abu Dhabi, Ajman, Dubai, Fujairah and Ras Al Khaimah — and carried out genetic tests to find out whether or not the insects had the resistance alleles for the gene in question.
Catching the flies was, said Dr Al Deeb, relatively easy. One method involved putting out fruit such as pineapple and mango to attract the creatures. They were then captured in a plastic zip-lock bag and placed in a refrigerator. Once the flies were made drowsy by the cold, they could easily be picked up and their DNA extracted for testing. Sweep nets and sticky traps are also commonly employed by researchers to capture flies.
In Ajman, in 70 per cent of flies, both alleles of the gene — one from each parent — were of the type that conferred resistance to pyrethroids, although the sample size was small.
In Dubai, the figure was 59.5 per cent; in Fujairah 44.4 per cent; in Abu Dhabi 41.9 per cent; and in Ras Al Khaimah 20 per cent. This means that the resistance alleles were found in all five of the emirates surveyed.
The resistance alleles cause the fly to produce a different form of a protein in the “voltage-gated” sodium channel across nerve cell membranes. Pyrethroids are neuropoisons because they induce changes in nerve membrane permeabilities to sodium and potassium ions in normal types of house fly. Thanks to their altered protein, flies with the resistance alleles are not affected in the same way by the pyrethroids.
If the resistance alleles become more common, the consequences could be severe.
Although some farmers have been using chemicals to control fly numbers for many years, and might believe there is nothing to worry about, Dr Al Deeb said his study indicated that the number of resistant flies could have the potential to grow.
“One day, the whole population, or most, will be resistant. It’s called insecticide failure. You lose one tool from your arsenal of tools,” said Syrian Dr Al Deeb, who has worked in the UAE for the past eight years after completing master’s and PhD degrees in entomology at Kansas State University, in the United States.
The numbers of flies tested in this study was relatively modest, at 122 in total, so Dr Al Deeb said municipalities around the country might want to consider carrying out their own study, with larger numbers. This could determine more accurately how widespread resistance alleles are.
Ultimately, results such as those in this study could prompt the authorities to promote different ways to control flies, instead of using pyrethroids.
Such alternative methods to control insects have, said Dr Al Deeb, become popular in other countries. These techniques are said to have multiple benefits: as well as preventing insecticide resistance from developing, they can reduce harmful effects on the environment and people from the chemicals.
“In the US ... they have resistance management programmes that go hand-in-hand with insect chemical control,” he said.
“Now we can start ... creating awareness among those that practice pest control, and hopefully more people will be interested in the topic.”
Alternative methods can include using types of bacteria and fungi that are parasites of insects to keep fly numbers down, or capturing the flies with traps, although the consistently high temperatures in the UAE means that certain methods used to control fly numbers in other parts of the world may not be effective here.
“We don’t have a silver bullet. We know the direction is non-chemical [methods of control], but this should be done by going through the literature and doing experiments. We can [find] answers by doing research,” said Dr Al Deeb.
Methods to control other pest insects could also come under the spotlight in future, as Dr Al Deeb is now turning his attention to the red palm weevil and the date palm fruit stalk borer to see how widespread pyrethroid insecticide resistance is among them.
newsdesk@thenational.ae
