The fruit fly is a generic term which includes several insect pests Diptera, like the Mediterranean fly, the cherry fly, or even that of the olive, the latter two being subservient to a single species of fruit tree. In contrast, the Mediterranean fly, Ceratitis capitata, can attack at least two hundred species of fruit. These are the maggots which, by feeding on the pulp, cause secondary rots, and are responsible for significant damage to the fruits and their premature fall.
Common features of fruit flies
Fruit flies are insects belonging to a single family (tephritidae) of 4500 harmful species, in the world. The adult fly, about 5 millimeters long, has a single pair of dark, mottled wings. The body, thorax and abdomen, presents transverse bands or various spots. The eyes are generally green or blue. The maggots, characteristic larvae of flies, are yellowish white and 7 to 8 millimeters long. The nymph, called pupa in Diptera, ovoid in shape, beige gray, measures a few millimeters.
Biology of the fly in direct relation with the fruits
It is at the pupa stage that the fly hibernates, buried in the ground. Depending on the region, spring warming and the species concerned, the first adult flies hatch between May and July. The adult female pricks the skin of the fruit, using her ovipositor, to lay one or more eggs. As soon as it hatches, the maggot enters the pulp to feed on it, and triggers a secondary rotting of the pulp, a sort of brown mash ... The surface of the fruit shows discolored and depressed areas. Fruits fall early or dry out on the tree. The harvest can be very largely compromised. In a second step, the maggots are extracted from the fruit, whether it has fallen or not, and then burrow into the ground, to carry out their pupation. Then the pupa turns into an adult fly.
Fruit trees victims of flies
The cherry fly, Rhagoletis cerasi, like that of the olive, Bactrocera oleae, each lay only one egg per fruit. But the first knows only one generation, while the olive fly can have three. The crop, in both cases, is spoiled by the traces of stings and rot spots on the fruits. The Mediterranean fly, Ceratitis capitata, lays up to thirty eggs per fruit and can develop eight consecutive generations in the year. Its attraction for a large number of fruit trees, added to its multiplication capacity during the summer, allows us to understand the worrying aspect of this pest in apricot, peach, citrus, fig ... plantations. memory, we can cite the comparable nuisance power of a fly originating in Sri Lanka, Bactrocera invadens, which has been causing incredible damage to the mango tree in particular in West Africa for the past ten years.
Fruit fly control methods
There are no specific methods for controlling flies. It is good to know that the period of fruit ripening seems to attract laying females, and that late varieties are often the most affected. Careful observation will guide the actions to be undertaken. Great vigilance, with the implementation of a surveillance strategy for adult fly outbreaks, will make it possible to assess the size of the populations, this in relation to the alerts expressed by plant protection organizations. Thus, one can place traps in the orchard (flycatcher or sticky plate with pheromones). If the populations are large, the control strategy using chemicals will have to be amplified. It is possible to suspend traps containing baits and insecticides, spaced every 10 trees for example, or to deposit the same mixture directly on the leaves of one tree in two. In the event of massive attacks by flies, it may be necessary to spray an insecticide on the entire tree (comply with the phytosanitary index of ACTA). Biological control is possible thanks to the importation of auxiliary insects, entomophagous enemies of these flies. Finally, to limit populations, it will be useful to harvest and eliminate the affected fruit, on the ground or in the tree, as much as possible. By Claire Schutz Croué