One of the limiting factors of fruit production are pests, some of them with quarantine importance, such as fruit flies. The most important species are the Mediterranean fly (Ceratitis capitata) and the South American fly (Anastrepha fraterculus). Since 2014, Drosophila suzukii (Matsumura), popularly known as the spotted-wing fly, has joined this complex.

The variations in the climatic conditions during the winter caused the populations of some groups of insects to present an erratic behavior, as is the case of this fly. Thanks to periodic monitoring carried out by specialists from INTA Concordia –Entre Ríos– its presence was observed in some establishments with blueberry crops of early varieties.

"The adults of this species measure from two to three millimeters in length and have red eyes, the color of the thorax is light yellow or brownish, and the abdomen has black bands," said Juan Pedro Bouvet, a researcher specializing in citrus and blueberry crops at the INTA Concordia–.

The males have dark spots on the wings, a characteristic that is not shared by the females. "It tolerates different climatic conditions and the wind favors its dispersal, since they are small flies," he added.

After copulation, the females look for healthy and ripe fruits to lay their eggs, which they insert inside them. "Each female can lay up to 21 eggs per day, and she does it by cutting the skin of the blueberry," Bouvet explained.

The openings caused facilitate fungal and bacterial infections, which contribute to the deterioration of the fruit. To this is added that, when they are born, the larvae feed on the pulp and benefit the appearance of yeasts that cause fermentation.

The range of hosts of the pest is wide, however, fine fruits (such as blueberries, cherries, raspberries, strawberries and blackberries) are the most chosen by the pest because they have delicate skin. The producer can see symptoms such as superficial wounds, softening, wrinkling and premature fall.

For Valeria Viana, specialist in plant health at INTA-Conicet, monitoring throughout the year, both in commercial crops and in alternative hosts, is the most important step to be able to determine the presence of the pest.

"In Argentina, the type of trap or the specific attractant for monitoring this pest has not yet been established, currently it is carried out through the use of both transparent and red traps with food attractants," Viana mentioned.

Control measures

The control guidelines recommended by the specialists include cultural practices such as eliminating food sources (whether from alternative hosts near the crop, such as the fruit of the crop that is not marketed), correctly managing the movement of the fruits, cleaning tools and machinery, avoid abandoned plantations, manage ornamental and wild hosts, carry out periodic monitoring and be in communication with neighboring productions.

They insist on complementing with mass trapping since it is a measure with low environmental impact and great effectiveness. "It consists of placing a high density of traps with the most specific attractant possible and thus capturing the largest number of females possible before they cause damage to the fruit," Bouvet explained.

With respect to chemical control, active principles for the control of Drosophila suzukii have not yet been authorized in the country. Physical control, such as the use of barriers or meshes, although they are effective, will be subject to the profitability of the producer. Finally, the specialists mentioned that the Sterile Insect Technique (SIT) and biological control with entomopathogenic fungi are being evaluated.