Adult vinegar flies vary (depending on the species and their source of feeding) from 3 to 4 mm long (25mm = 1 inch), are light yellowish brown to dark brown in color and may have dark markings on the back of the thorax in the form of spots, blots or lines (Fig. 1). Most have reddish eyes. The antennae have three segments, the third segment is oval and has a branched edge (like the structure of the hair), where the branches are relatively long. The abdomen is typically darker than the thorax due to the presence of dark bands in the segments.
The larvae, which are worm-shaped, are 2.5 to 4.5 mm long, cream-colored, lack a sclerous capsule on the head and are tapered from the posterior area to the head. They have vents (breathing structures) located in extended fleshy tubes found in the last segment of the body.
The "vinegar fly" or "drosophila" is the transmitter of the disease called "acid cluster rot". Their damages are indirect, but no less serious. Although it is an insect that until only a few years ago caused only sporadic damage in isolated vineyards, in recent times it has spread and has become a problem of some importance in the plantations of the Mediterranean coast.
The larvae feed mostly on the yeast found in liquefied and fermented items. Tomatoes and bananas that have gone over ripe are commonly infested, as are potatoes and onions in a state of decomposition. The liquid left in the bottom of the beer cans, which are stored for recycling, can hold the larvae of the vinegar fly. Flies can procreate on any substance that is in a state of decomposition or acid such as wet mops and the accumulation of food particles under or behind kitchen utensils. Drains that have a gelatinous growth of slag are also conducive to the development of an infestation of vinegar flies. Typically, the larvae become pupae outside their food source, after having been feeding for about a week or so. In a few days an adult fly emerges and becomes a sexually active adult in two days. Its life cycle is completed in just eight days at 85º F.
The elimination of breeding places for flies is of primary importance. Although nebulous insecticides and sprayers can kill adult vinegar flies, larvae will continue to develop and new adult flies will emerge unless the potential sources (described in the previous section) are discovered and eliminated.
During the summer months, adult flies will be attracted by the lights shining through the windows. Due to the small size of the adults, they can access through the regular wire mesh of the windows. By installing 16-mesh or finer mesh, they can reduce the number of flies that enter a structure.
In the surroundings, remove fruits such as apples, pears and tomatoes that have fallen on the ground. At home, store fruits and vegetables in the refrigerator. Thoroughly rinse cans, containers and bottles before recycling to remove potential sources of food.
Distinction of sex in adults
There are differences between male and female individuals, which allows distinguishing them from each other. The tip of the abdomen is elongated in the female and rounded in the male. After a certain time, the abdomen of the females distends due to the maturing eggs it contains; the flies of this sex are recognized by this at a glance. In many stock, including the wild type, the darker marks on the abdominal segments have a sufficiently different distribution in each sex to allow their separation without the need of the microscope. The abdomen of the female contains seven visible segments; while the male contains only five.
The males have the so-called sexual combs, a brush of approximately ten strong black mushrooms in the basal joint of the tarsus of the first pair of legs. Through these characters, it is possible to distinguish the male from the female, either by visual inspection or, in doubtful cases, with the help of low-magnification lenses.
Abdominal pigmentation is also taken into account as a criterion of differentiation between males and females, but for this we must be very careful because in flies that are not fully developed this pigmentation is not total, so there can be confusion.