Both the South American fly and the Mediterranean fly prefer to ovipositar in ripe fruits, with physicochemical characteristics that correspond to maturation. Field monitoring in this period is an important control tool.
Fruit flies are limiting pests for the expansion of national fruit growing and are among the main insects that cause fruit damage and restrict exports due to quarantine barriers imposed by importing countries. Currently, Brazil exports approximately 2% of the fruits produced, and most of the exports are related to mango, apple, table grape and melon fruits. Although the presence of fruit fly is not the only obstacle that hinders exports, it is undoubtedly the main challenge to be overcome to increase the quality of the fruits produced and the sale to the foreign market.
In 2015, the Ministry of Agriculture, Livestock and Supply (Mapa) created the National Program to Combat Fruit Flies (PNMF) focusing on the species of Anastrepha (A. fraterculus, A. obliqua and A. grandis) native to the American continent, in the carambola fly (Bactrocera carambolae), a quarentenarian pest present, restricted to the states of Amapá, Roraima and Pará. The program also focused on the Mediterranean fly (Ceratitis capitata), an exotic pest, for more than 100 years present in Brazil and with great distribution in the national territory. Although several species of flies cause damage in Brazil, the two with greater agricultural importance are the South American fruit fly and the Mediterranean fly, considered quarentenian pests for the member countries of the European Union, for the United States and West Asian countries, the main importers of fruits produced in Brazil.
In southern Brazil, two changes that have altered information on the occurrence of fruit flies in recent years have been observed. The first refers to the fact that C. capitata has always been related as a secondary species. However, studies show that for border regions, both with Argentina and Uruguay, most of the flies caught are of the species C. capitata. The second change is related to the time of occurrence of A. fraterculus in orchards. Traditionally, no citrus damage was observed by this species and in late autumn the fruit fly population was considered low. In the last three years, high infestations have been recorded in May and June, compromising citrus cultivation in all regions of the state. It is estimated that the average loss has reached 40% of production.
The symptoms of the attack of fruit flies begin with the appearance of softened spots on the bark and discoloration in the region of the posture, with subsequent change in coloration, which goes from brown to brown. In citrus crops the level of infestation varies according to the cultivar, the location of the orchard and the climatic conditions. However, citrus has mechanisms that can affect the development and reproduction of fruit flies, such as the physicochemical characteristics of fruits (color, weight, acidity, among others).
In this sense, laboratory studies were carried out in order to verify the time of occurrence of the South American fly and the Mediterranean fly in fruits of orange cultivar Navelina. The preference for oviposition in three citrus species (orange, tangerine and lemon) was also determined, as well as the relationship of oviposition, of the two pests, with the thickness of the citrus peel.
Development related to maturation stages
Fruits of navelina cultivar orange trees obtained from commercial orchards located in the municipality of Rosário do Sul, In Rio Grande do Sul, were collected. After flowering, the fruit development was monitored to characterize four phenological stages, defined from their physical and chemical characteristics. The four maturation stages were defined as: I) fruit with approximately 5cm in diameter (fruit with 3/4 of the final size); II) fruit with 6cm to 7cm in diameter (green fruit close to final size); III) fruit in the change of color green to yellow and IV) final maturation, where the fruits present all peel with yellow-orange color (Figure 1). For the physical and chemical analyses, the weight (g) and diameter of the fruits (cm), the thickness of the peel (mm), the pH, the sugar content (expressed in °Brix) and the acidity (expressed as a percentage of citric acid) were determined.
Of the maturation stages of Navelina orange fruits evaluated, infestation was verified only in stage IV (end of maturation). The infestation rates at this stage were 0.72 pupae/fruit and 2.05 pupae/fruit for Anastrepha fraterculus and Ceratitis capitata, respectively.
The data demonstrate the higher susceptibility of Naveline orange fruits when the maturation of citrus fruit is more advanced, in view of the decrease in acidity and the increase in the sugar rate. As occurred in the present study, the total acidity decreased from stage I to IV from 0.85 to 0.52, as well as the sugar rate increased from 9.9 to 11.1 (Table 1).
Development in ripe fruits
Sixty Naveline orange fruits from each maturation stage were offered for each fruit fly species for a period of 24 hours. After exposure, the fruits were individualized in plastic containers with perforated lid containing vermiculite, where the development of the immature was allowed to proceed to the counting of pupae and their separation for observations of biological parameters.
It was observed that the duration of the egg-adult period of A. fraterculus and C. capitata in Naveline orange fruits was on average 30 days. The average number of eggs (fecundity) of A. fraterculus was higher than that of C. capitata. However, fertility (ability to generate larvae) was similar for both species, around 60%. After emergence, the females of fruit flies took an average of 15 days to begin oviposition in the fruits, and it is therefore important to monitor the area to identify this moment and perform the control before. Most posture (80%) it was performed in the first 15 days of the oviposition period, and the oviposition peak occurred on the 11th day (299 eggs) for A. fraterculus and on the 16th day for C. capitata (269 eggs).
Preference for oviposition in citrus fruits
Fruits of three citrus species (Naveline orange, Clemenules mandarin and Sicilian lemon tree) were offered for each species of fruit fly, for a period of 24 hours. After the exposure period, the fruits were removed for egg counting.
It was verified that A. fraterculus preferred ovipositar in tangerine fruits and C. capitata in orange fruits. In lemon fruits there was no oviposition by both species. When the influence of the presence of lemon on the oviposition was analyzed for both orange and tangerine, there was no significant difference in the number of eggs of A. fraterculus, indicating that there was no influence on the choice of fruit by this species. For C. capitata, it was found that in orange there was greater oviposition when this fruit was offered in combination with lemon, and there seems to be a stimulus for oviposition when in this situation. Considering that the fruiting of Naveline orange and Sicilian lemon tree occurs in the same period (February to July), there may be a higher probability of oviposition in orange, when these citrus cultivars are present in the same area. The choice of the host by insects is influenced by chemical and visual stimuli. Thus, the females of C. capitata may have identified compounds unsuitable for the development of their descendants in Sicilian lemon fruits.
Influence of shell thickness
To evaluate the relationship between the oviposition depth of fruit flies and the thickness of citrus peel, naveline orange and Clemenules tangerine were offered to females of A. fraterculus and C. capitata for 24 hours. After the exposure period, the fruits were analyzed under stereoscopic microscope to identify the location of the eggs in each fruit.
It was verified that the thickness of the peel of Naveline oranges and tangerine Clemenules did not influence the oviposition of A. fraterculus and C. capitata. Both species did not lay their eggs inside the citrus fruits. The females placed the eggs in the region of the flavedo (outer layer of the bark) of orange and between the albedo (fibrous layer of the bark) and the flavedo in tangerine. The higher depth of laying of the eggs in tangerine may be related to the lower firmness of the shell, compared to the orange, allowing greater larval survival due to the lower difficulty of the larva migrating from the shell to the pulp.
The definition of the maturation stages of a cultivar allows to relate the conditions in which the fruit is suitable for infestation. Although the development of fruits in the field is related to a number of factors, such as temperature, rainfall and radiation, the physicochemical characterization can provide an indication of the period in which larval development of fruit flies occurs and thus guide the establishment of control strategies. For the cultivar Navelina, it was found that the infestation occurs only at the last maturation stage (bark with orange-yellow coloration), corresponding to the period from June to July in the state of Rio Grande do Sul.
With this, it is possible to verify that both the South American fly and the Mediterranean fly prefer ovipositar in ripe fruits, with physicochemical characteristics that correspond to maturation. Thus, the monitoring, in the field, during this period, is an important tool to avoid losses by infestation of fruit flies.
Source: Cultivar Group