Damage caused by the South American fruit fly in apples

The apple is the second most important temperate fruit for trade in natura, both in the national and international markets. The South region concentrates around 98% of Brazilian production, which comes from the Gala and Fuji cultivars or their clones. Among the major fruit producing centers, the regions of Vacaria (RS), Palmas (PR), São Joaquim and Fraiburgo (SC) stand out. The South American fruit fly, Anastrepha fraterculus (Diptera: Tephritidae), is the main insect pest of apple trees, constituting a constant concern in crops, both due to the damage it causes to the fruits and due to the quarantine measures imposed by importing countries. Furthermore, the damage caused by the pest leads to increased costs, due to frequent applications of insecticides and production losses.

In apples, the damage of A. fraterculus It is caused both by oviposition in the fruits and by the carpophagous habit of the larvae, which during feeding create galleries, altering the flavor, causing premature ripening, rotting and falling. Furthermore, the wound made during oviposition can lead to infection by fungi and bacteria, making them unsuitable for sale and consumption.

Damage can be observed in apples that are still green, approximately 20mm in diameter, even those close to harvest. Even without surviving in immature fruits, the larvae, when they hatch, cause the death of tissues close to the punctures, causing them to grow deformed, which reduces their commercial value.

Population fluctuation

The population fluctuation of A. fraterculus varies between different years and regions, as well as depending on meteorological variables and the ripening period of the fruits.

In Santa Catarina, in apple orchards, collections of adults in traps can begin in September and continue until April. However, the start of captures will depend on the fruiting phenology of alternative hosts present in different regions, which are responsible for the emergence and repopulation of flies in orchards.

In the Caçador region (Santa Catarina), a higher density of flies is observed in January and February, which is related to the beginning of maturation of early and intermediate apple tree cultivars. The last individuals of A. fraterculus they are typically recorded in April and collected again in November or December. During the period in which apple trees enter dormancy, in the month of May, temperatures begin to decrease, with the average falling below 13°C.^oC until August, exerting influence on the insect's bioecology (longevity and fecundity). As a result, the occurrence of temperatures below the lower threshold, from May to September, is detrimental to the development of A. fraterculus. Research results indicated that in Caçador, where the average annual temperature is around 16^oC, it is estimated that A. fraterculus it could have had 8,3, 7,7, 7,8 and 8,7 generations in 2009, 2010, 2011 and 2012, respectively.

In southern Brazil, after the winter period, fruit fly populations normally begin to recover in native forest areas, where hosts allow these insects to multiply, which, in turn, begin to migrate to orchards. in search of oviposition sites. In the forests, a great diversity of hosts can be found, especially from the Myrtaceae family. The fruiting of these plants is decisive in the size of the fruit fly populations that will colonize apple orchards, as they contribute to reproduction occurring practically all year round.

In Caçador, the main hosts of fruit flies are: the Rio Grande cherry tree (Eugenics involucrata), the pitangueira (eugenia uniflora), the guabirobeira (Campomanesia xanthocarpa), the mountain guava (acca sellowiana), the capoteira or seven-capotes (Campomanesia guazumifolia), the araçazeiro (psydium spp.), uvaieira (Eugenia pyriformis), the guabijeiro (Myrcianthes pungens) (Myrtaceae), the ingazeiro (Inga spp.) (Fabaceae) and the araticunzeiro (Annona cacans) (Anonaceae), whose fruiting periods precede or coincide with those of the apple tree.

Fruit fly hosts can be classified into two groups: multipliers, which allow the development of large quantities of insects, and alternative hosts, which are occasionally infested, generating few individuals for the population. In the apple-producing region of Vacaria (Rio Grande do Sul), Rio Grande cherry, mountain guava and guabirobeira are considered multiplier hosts, while araçazeiro and uvaieira are alternatives. In Caçador, in addition to the three mentioned as multipliers for Vacaria, the araçazeiro is also included, with the others being considered alternatives.

The Rio Grande cherry tree is the first multiplying host to bear fruit and, thus, generate flies that will disperse to apple orchards. Therefore, the fruiting of this plant in November is an indication of the beginning of the occurrence of fruit flies on apple trees in the Caçador region.

In the period of physiological ripeness of apples (beginning of February to mid-April), it appears that there is overlap with the fruiting of several hosts. Therefore, throughout the period in which there are ripe fruits in guava, capoteira, araçazeiro, uvaieira, guabijeiro, ingazeiro and araticunzeiro, there is a supply of apples in the orchards. Furthermore, the mountain guava, araçazeiro and araticunzeiro finish producing fruit along with the late apple trees.

The presence of alternative hosts located in the surrounding forests influences the population dynamics of A. fraterculus and, the lack of knowledge about its phenology makes it difficult to predict infestation and the time of occurrence of the pest in each harvest. Due to the fact that fruit flies cause damage to fruits that are still green and because the incidence is high during the maturation period of early cultivars, in January and February, monitoring of adults should begin soon after flowering and be maintained until all are harvested. the fruits of the orchard, making control decision-making possible.

Management and control

In commercial orchards, fruit fly control is carried out based on the population level of the pest and monitoring has been done with traps containing food attractants, such as grape juice diluted to 25% and hydrolyzed protein (3% to 7 %). Hydrolyzed protein (3%) and Torula yeast (three tablets/400ml of water) were the most efficient attractants in capturing fruit flies, in studies carried out in apple orchards in Caçador and Fraiburgo. These attractants presented less variation in composition and maintained homogeneity of capture during the crop cycle, when compared to grape juice.

In the southern region of Brazil, it is recommended that traps be installed from September to October, on the outskirts of orchards, with a control level of 0,5 flies/bottle/day.

In apple trees, the main ways to control fruit flies are the use of toxic baits and the spraying of insecticides under cover. The baits are applied around the orchards and aim to prevent insects from entering the production areas.

Apple producers have few product options for chemical control of fruit flies and this scenario tends to worsen in the coming years, given that, among the phosphorus insecticides registered for control on apple trees, only phosmet has no restrictions.

Apple importing countries have demanded a reduction in the levels of agrochemical residues in the fruits. Therefore, one of the goals of Integrated Apple Production (PIM) is to establish technical production standards so that the Brazilian fruit remains competitive in the international market. The European community annually determines the permitted active ingredients and the limits of agrochemical residues tolerated in fruits sold in those countries, which is currently one of the main concerns of the production sector, especially in relation to restrictions on insecticides used in apple production.

An alternative for controlling flies in small areas is fruit bagging, which has shown promising results, especially in the organic production system. This practice, in addition to not affecting quality, preserves the appearance and improves the organoleptic quality of the fruits.

Collecting fallen fruit and storing it in trenches covered with screens that retain adults and, at the same time, allow natural enemies to pass through, is another practice that can contribute to reducing fruit fly infestation in orchards.

This article was published in issue 88 of Cultivar Hortaliças e Frutas magazine. Click here to read the edition.