Attractive fruit fly trap

Over the last ten years, the cultivation area for fine table grapes, in the protected cultivation system in the Serra Gaúcha region, has increased by an average of 80 hectares per year, totaling around 800 hectares in the 2012/13 harvest (Figure 1).

Figure 1 - Areas of vine production under protected cultivation in the Serra Gaúcha region (RS)

Photos: Ruben Machota Jr

Much of the increase in cultivated area is due to the adoption of new technologies by producers, with emphasis on those focused on the production of fine table grapes, with high added value, who seek fruit with better visual appearance, health, absence of residues chemicals and adequate maturation.

The South American fruit fly Anastrepha fraterculus (Wied., 1830) (Diptera: Tephritidae) is one of the main insects that can affect status of pest when damaging the berries of fine table grapes Vitis vinifera L. from cultivar Itália, the main grape variety grown under plastic in the region (Figure 2).

Figure 2 - Cultivation of vine cultivar Itália managed under protected cultivation: general appearance of bunches (A) and adult Anastrepha fraterculus in berries (B)

Photos: Ruben Machota Jr

The damage is attributed to adult females, which pierce the epidermis of the berries to carry out oviposition, or to larvae, which destroy the pulp by developing and moving inside the fruits, forming galleries, which are easily observed in cultivars with clear epidermis (Figure 3 ). Another additional damage is the fall of green berries due to punctures (perforation caused by the introduction of part of the ovipositor into the epidermis of the fruit) carried out by females.

Figure 3 - Damage caused by the ovipositor of the South American fruit fly Anastrepha fraterculus (A) and galleries caused by larvae in vine berries of cultivar Itália (B)

Photos: Ruben Machota Jr

In addition to the direct damage caused by punctures and galleries, the fruit fly also helps in the dispersion of phytopathogens that cause rot that are inoculated during oviposition, increasing harvest losses (Figure 4).

Figure 4 - Berries intact even after spraying a 1x10 suspension⁶ conidia of Botrytis cinerea Pers. (A); berries with rot resulting from the association between oviposition of Anastrepha fraterculus and the spraying of conidia of B. cinerea (B)

Photos: Ruben Machota Jr

Real Time

One of the fundamental points for establishing a management strategy for South American fruit flies in grapevines is monitoring them. The presence of fruit flies in the vineyard is detected through the use of attractive substances, especially fruit juices, hydrolyzed proteins or torula yeast, placed inside McPhail traps. However, significant flaws in the control of A. fraterculus were recorded in orchards that use juices as attractants. Hypothetically, fruit flies are not attracted to the traps due to the high concentration of volatiles emitted by ripe or decomposing fruits present in the vineyard, thus reducing the effectiveness of monitoring. In these cases, even with the insect present in the vineyard, the traps cannot attract it, resulting in losses to the producer.

The evaluation of the attractants available on the market for monitoring fruit flies demonstrated low attractiveness for grape juice and corn glucose, in addition to an equivalent capture between torula yeast and traditional hydrolyzed protein (Figure 5). However, the attractiveness of a new hydrolyzed protein formulation (CeraTrap, BioIbérica S.A.) is worth highlighting (Figure 5). In addition to capturing adults higher than traditional attractions, it remains stable for a period of up to 60 days, without the need for replacement, proving to be a new tool for monitoring the species in culture.

Figure 5 - Average number of South American fruit fly adults Anastrepha fraterculus captured per day (MAD) in McPhail traps baited with different food attractants at the end of 26 weeks of evaluation (November 2012 to May 2013) in the grapevine crop. Description: CeraTrap (BioIbérica S.A., without dilution, replacing the attractant every 60 days); Torula (Isca Tecnologias Ltda, six tablets/L), BioAnastrepha (BioControle – Pest Control Methods Ltda, 5%), corn glucose (Yoki Alimentos Ltda, 10%) and red grape juice (Embrapa Uva e Vinho , at 25%), changed weekly. *Averages followed by the same letter do not differ according to the Tukey test at 5% significance.

Fruit fly management

In general, fruit fly management has been carried out through the use of organophosphate insecticides sprayed under cover, associated with the use of toxic baits from the capture of adults in monitoring traps. However, due to the withdrawal of these insecticides from the market, the effectiveness of overhead spraying has been limited. The new insecticides available have not been effective in controlling the larvae present inside the fruits. This fact has forced producers to use other management strategies, with emphasis on the use of toxic baits.

Due to the stability presented by the CeraTrap hydrolyzed protein formulation (attractiveness to adults maintained for a period of up to 60 days), the old technique of mass capture is once again the subject of studies for the control of the South American fruit fly. This technique, described for the first time in Brazil in the 1980s using fruit juice as an attractant, is based on controlling adults through the installation of a high density of traps per area.

To use the technique, it is recommended to use traps made from two-liter terephthalated polyethylene (PET) bottles, transparent (crystal) or green, containing four circular holes measuring 7 mm in diameter, located in the middle portion of the bottle, distanced equidistant from each other, inside which the attractant is placed without the need to add chemical insecticides (Figure 7).

Figure 7 - Trap made from a two-liter PET bottle. Detail of the 7mm diameter circular holes (A). Arrangement of the trap in the field with the attractant inside (B)

Photos: Ruben Machota Jr

Traps must be made using clean bottles, with translucent walls and without labels. The holes can be made with the help of galvanized wire with a gauge of 0,89mm, molded to form a circle of 7mm in diameter connected to a rod of approximately 20cm.

The metal circle formed with the galvanized wire must be heated red-hot and placed against the surface of the bottle. This procedure promotes the formation of a hole with smooth, well-defined edges. Other procedures, such as the use of drills coupled to drills, should be avoided because, although they appear to be more practical, they create irregular holes that make it difficult for the insect to enter the trap and reduce captures.

The volume of attractant to be used inside each trap must be 300ml, without dilution. Its replacement is recommended during the culture cycle as the product evaporates, seeking to maintain the initial volume.

Experiments carried out in vineyards of fine table grapes of the cultivar Itália under protected cultivation in the Serra Gaúcha region demonstrated that the average volume evaporated by trap in the hottest months of the year (December and January) is around 7,5 ml per day . Depending on the cultivar, the fly attack period (pea grain at harvest) is approximately 3 to 3,5 months (90 to 105 days), and the total evaporated per bottle can reach 900ml. It is important to highlight that this volume of attractant per trap must be considered when planning the quantity to be acquired per harvest.

Although the trap density (number of traps per hectare) can be adjusted according to the peculiar characteristics of each vineyard (infestation history, location of the area and presence of native fruit fly hosts close to the crop), it is suggested a density of 100 traps/ha.

The location of the traps in the vineyard is another point of fundamental importance in the correct use of the technique. Due to the different environmental characteristics promoted by protected cultivation, in particular the physical barrier of the plastic cover positioned over the plant canopy, it is recommended to place the traps on the edges of the vineyard, hanging from the first plant immediately below the plastic cover. In this way, a “barrier” is established that significantly reduces the entry of fruit flies into the vineyard. The height at which the traps are placed is 1,5m to 1,7m, in order to facilitate exchange procedures and replacement of the attractant.To facilitate the placement of the traps in the vineyard, a 0,5mm enamelled copper wire 30cm long can be tied to the neck of the bottle (Figure 8E).

It is essential that producers monitor the infestation throughout the harvest by observing the insects captured in the traps. By carrying out this procedure, it is possible to identify infestation hotspots and, consequently, reposition the traps, increasing the density in these locations.

It is recommended that the traps be maintained until the end of the harvest. However, in places where there is a great diversity of fruit fly hosts and which have staggered fruiting throughout the year, maintaining traps throughout the year helps to reduce infestation.

After use, the bottles must be cleaned and stored in an appropriate place to be reused in the following harvest, or they can be installed in other crops, especially those close to forest edges or alternative fruit fly hosts. Due to the pasty composition acquired by the attractant over time, there is a need to add a few drops of neutral detergent to the water used to clean the traps at the end of the season.

In experiments conducted in fine table grape vines of the cultivar Itália grown under plastic cover in the 2011/12 and 2012/13 harvests in the Serra Gaúcha region, a significant reduction in damage caused by fruit flies was recorded in comparison to conventional management. which is based on the application of insecticides under coverage (fenthion), demonstrating the feasibility of using this technology in vine cultivation (Figure 8).

Figure 8- Percentage (%) of vine clusters of cultivar Itália with the presence of galleries caused by larvae of Anastrepha fraterculus during the harvest period. Caxias do Sul (RS)

Description: CeraTrap (mass capture technique using CeraTrap hydrolyzed protein^® at a density of 100 traps/ha on the edges of the vineyard); Conventional (conventional treatment using the organophosphate insecticide fenthion, respecting the withdrawal period of 21 days).

Final considerations

The hydrolyzed protein CeraTrap is an alternative for monitoring and controlling the South American fruit fly in protected grapevine cultivation through the use of the mass capture technique.

The great attractiveness presented by the CeraTrap hydrolyzed protein makes it possible to reduce the population of fruit flies inside vineyards grown in the protected cultivation system. This population reduction results in less damage to the berries and, indirectly, in a reduction in the labor used to thin the berries into fine table grapes.

Click here to read the article in issue 81 of Revista Cultivar Hortaliças e Frutas.