Fruit flies (Tephritidae and Drosophilidae)

Words by Karen Fick & Simon Difford

Fruit flies plague bars. They find their way into bottles - especially wine and vermouth bottles, and swarm over cut fruit and beer taps. However, a good regime of cleaning, covering and setting traps should eradicate them from any bar.

Odour detectors in these tiny creatures are brilliantly evolved to detect fermenting fruit from a great distance and because they are so tiny they can get in through tiny crevices around windows or doors. And you only need one, because the female fruit fly can lay up to 500 eggs. Their other port of entry is on the fruits and vegetables that you bring home already laden with eggs, which then hatch incredibly quickly, going from egg to adult in just eight days

Beer lovers

Fruit flies are particularly attracted to products associated with fermentation. Scientists have found that receptors in their mouth-parts sense glycerol, a sweet tasting sugar alcohol compound that yeasts make during fermentation. It's why they love spilled alcoholic beverages and particularly beer and they can ruin the alcohol fermentation process, turning beer or wine into vinegar. But any trace of mess we leave or even damp mops and sponges will provide the perfect place for them to lay their eggs as this environment will provide food for the larvae which will feed on any decaying matter.

How to eradicate flies from your bar

• Meticulously clean when breaking down at the end of each shift.
• Cover cut fruit with cling film or keep in refrigerator. Never leave out overnight.
• Keep beer drip trays emptied and cleaned.
• Don't leave standing water over night. Bleach sinks drain holes every night.
• Don't leave out wet rags, sponges or mop heads. Store in sealed containers.
• Seal bottles at end of shift (and ideally during shift for all bottles not in rail).
• Prepare fruit fly traps (see video) and position near fruit and beer fonts.
• Cleanliness and cling film are the best weapons against fruit flies.

The family

There are two families of fly that are commonly referred to as fruit flies. The first, Tephritidae is a family of large, colourfully marked flies including agricultural pests. Then there are Drosophilidae, a family of smaller flies which contains more than 4,000 species, amongst which is Drosophila melanogaster or the common fruit fly. Drosophila melanogasterar are generally considered to be a nuisance rather than a pest, a pest being broadly defined as a plant or animal detrimental to humans or human concerns.

Adult Drosophila melanogasterare are 3 to 4 mm long and have red eyes, a tan thorax and the abdomen is black on top and grey underneath. Fruit flies can appear to be brown or tan in colour.

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Life cycle

Like other fly species, fruit flies have a four-stage life cycle: egg, larvae, pupa and fully formed adult. The early stages last just a few days and fruit flies can complete their development in as little as week in ideal temperature conditions. The entire life cycle is about 25 days or so depending on environmental conditions.

The female fly probes numerous sites before deciding where to lay her eggs. Her location of choice will be on the skin of very ripe or fermenting fruit but she will also lay in moist areas such as the slime layer inside slow-draining plumbing, or on an damp mop or sponge. Just twenty-four hours later the eggs hatch into small, white larvae that eat from their nesting site for four days. Fruit fly larvae undergo moulting stages during which they shed the head, mouth, cuticle, spiracles and hooks. The mature larvae then crawl away from the feeding material to a nearby dry spot for the next developmental stage.

The larval skin now darkens and develops into a hard case called a puparium. During this pupa stage, which takes approximately four days, the legless larvae grow six legs and a pair of wings. Twenty-four hours before the adult fruit fly emerges from the puparium, the red eyes and folded wings are visible through the surface which then turns black. After forcing their way through the puparium, adults are light in colour and have elongated wings and abdomens. Within a few hours, these new adult fruit flies will darken.

Approximately 48 hours after emerging from the puparium, female fruit flies are sexually mature and can begin breeding and laying eggs. Adult fruit flies are fertile for their entire life span of about 10 days. Female fruit flies can store sperm from multiple inseminations for use in future egg productions.

A scientists dream organism

Drosophila melanogaster is an important model organism (a model organism is a species that is studied to understand the biology of other organisms, often humans) and are used extensively for studies concerning genetics, development, physiology, ecology and behaviour. The rapid life cycle allows researchers to study the effects of an experiment over a number of generations and to follow mutations which are quite common. Fruit flies share 75% of the genes that cause diseases within humans and researchers have manipulated genes in the fruit fly to extend their lifespan so perhaps one day research on them will be of real benefit to all of us. Fruit flies have only four pairs of chromosomes (humans have 23).

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