Fruit flies
Also known as Vinegar flies, Drosophila, Oriental fruit fly, Bactrocera dorsalis
In short
Two quite different insects are called fruit flies. Vinegar flies (Drosophila) are tiny nuisance flies that breed in fermenting fruit and rubbish indoors and do not harm healthy plants. True fruit flies such as the oriental fruit fly (Bactrocera dorsalis), common in Southeast Asia including Malaysia, lay eggs inside ripening fruit and are serious pests of fruit trees.
How it looks
Vinegar flies are about 3 mm long, with bright red eyes, a tan head and thorax and a darker banded abdomen; they hover around fruit bowls, bins and drains. The oriental fruit fly is larger, about 8 mm, with yellow and black markings on the thorax and abdomen and a dark T-shaped mark on the abdomen; females have a pointed egg-laying tube. Its larvae are pale maggots found inside the flesh of damaged fruit.
Signs
Vinegar flies: small flies clouding around ripe fruit, compost caddies, drink residues and bins; they are not a problem of potting mix. Oriental fruit fly: small puncture marks on ripening fruit, soft rotting patches, maggots in the flesh and premature fruit drop.
Life cycle
Vinegar flies can develop from egg to adult in as little as eight days at about 29 °C (85 °F); eggs hatch in one to two days and larvae feed for five to six days in fermenting material. Oriental fruit fly females lay batches of about 3–30 eggs under the skin of ripening fruit and typically lay over a thousand eggs in a lifetime; larvae feed inside the fruit, allowing rot to set in.
What favours it
Vinegar flies: overripe or rotting fruit and vegetables, drink residues, unsealed compost and damp organic waste indoors. Oriental fruit fly: fruiting trees such as mango, papaya and avocado in warm climates, especially where fallen fruit is left to rot.
Prevention
- Indoors, keep fruit refrigerated or eaten promptly, rinse containers and keep compost and bins sealed.
- Outdoors, pick up and destroy fallen and damaged fruit rather than leaving it under trees.
- Bag or wrap developing fruit in paper or plastic to stop egg-laying, and harvest promptly.
Treatment
Start with the first step and move down only if the problem persists.
- Vinegar flies: remove the breeding source first; populations fall within days. Trap the remaining adults in a jar baited with vinegar, beer or mashed fruit and fitted with a paper funnel.
- Oriental fruit fly: combine sanitation and fruit bagging; male lure traps (methyl eugenol) and parasitoid wasps such as Fopius arisanus are used in area-wide control.
Pros and cons
Cons
- Vinegar flies are a household nuisance.
- Oriental fruit fly larvae ruin fruit and can make a whole crop unusable.
Look-alikes
- Fungus gnats
- Dark, long-legged, mosquito-like flies that rise from damp potting mix.
- Shore flies
- Black, sturdy flies with spotted wings found where algae grows on wet mix.
Affected plants
Vinegar flies: no living plants; damaged or fermenting fruit only. Oriental fruit fly: more than 200 fruit and nut plants, notably mango, papaya and avocado.
Related
Sources
Written in our own words from these sources. Check a product label before using any treatment.