Risks and losses caused by cucurbit fly attack

In most cucurbit producing regions, the South American cucurbit fly occurs Anastrepha grandis (Diptera: Tephritidae), known for being one of the main pests that attack fruits of native or introduced cucurbits. Of neotropical origin, this insect is present in South and Central America and has been reported in Argentina, Bolivia, Brazil, Colombia, Ecuador, Panama, Paraguay, Peru and Venezuela. In Brazil, this insect occurs mainly in the South, Southeast and Center-West regions. The injury is always on the fruits of cucurbits, caused by larvae and females that lay eggs just below the epidermis. There are cases in which females can deposit up to 100 eggs in a single puncture. After hatching, the larvae feed on the pulp, forming galleries and, due to the opening made by the ovipositor, rot-causing microorganisms enter and the fruits rot (Figure 1). The presence of just one larva is enough to make the fruits unsuitable for consumption, commercialization and industrialization. After completing larval development, the insects abandon the fruit and pupate in the soil or among decomposing material, when the adults emerge after a few days.

Photo: Anderson Bolzan

Figure 1 - Damage caused by Anastrepha grandis in trunk pumpkin. A – Yellow pumpkin, due to larval development inside; B – Pumpkin cut in half. The circle shows a larva of A. grandis and the arrows demonstrate the galleries made by the larvae

A. grandis It has holometabolic development, going through the egg, larva, pupa and adult stages (Figure 2). The development of the egg-adult period of A. grandis in pumpkin at 25ºC it takes approximately 41 days, this duration being divided into 3,93 days for the embryonic period, 17,7 days for the larvae and 19,7 days for the pupal stage. Males live an average of 148 days and females 52 days, when evaluated individually (Silva & Malavasi, 1996).

Currently, at the Entomology Laboratory of Embrapa Clima Temperado in Pelotas, Rio Grande do Sul, experiments are being carried out with the purpose of evaluating the development of A. grandis in different hosts and temperatures, where it has been proven that this insect develops in different genera of cucurbits. However, its best development is noted in hosts of the genus Cucurbita, such as stem pumpkin, pumpkin and hybrid pumpkin “Tetsukabuto". Regarding temperatures, the best development for the immature stages occurs at temperatures close to 25°C, although development also occurs in the thermal range of 15ºC to 30°C.

Photos: Paulo Lanzetta

Editing: Fernando Jackson

Figure 2 - Biological cycle of Anastrepha grandis with average length measurements for each stage of development

The presence of this insect in cucurbit production areas intended for export may represent quarantine restrictions, which causes economic damage. These losses can vary greatly according to the relevance of the crop in each country or region. Thus, several regions of Brazil interested in exporting cucurbits have implemented pest-free areas (ALP) and risk mitigation areas (SMR), in an attempt to meet the requirements of importing countries, regarding the absence or low population of the pest. , respectively.

Pest-Free Area and Risk Mitigation Systems

The threat to the export of cucurbits due to the presence of A. grandis in producing regions initially encouraged the project to monitor A. grandis in 1985 in the state of Rio Grande do Norte (RN). After eight years, the absence of this pest was demonstrated through field monitoring and fruit cutting. From then on, the United States Department of Agriculture authorized Brazilian exports of melons produced in the Free Area of A. grandis from the state of Rio Grande do Norte. Since 2003, twenty municipalities have been recognized by the Ministry of Agriculture, Livestock and Supply (Mapa) as ALP of A. grandis, 13 in the state of Rio Grande do Norte and seven in the state of Ceará. In addition to this area where the fly does not occur, there is a “buffer area” around these municipalities with approximately 15.000km², where monitoring and the establishment of phytosanitary barriers are also carried out to prevent the entry of fruits infested with the insect.

The SMR is adopted by producers who wish to export their production to countries that establish requirements that the fruits do not present a quarantine risk due to the presence of pests, allowing the presence of the pest in a low population and with the adoption of differentiated pest management. . Monitoring consists of several procedures aimed at certification and traceability, such as, for example, the use of traps throughout the crop cycle and while crop remains remain. Currently, there are some regions in seven states of the Federation that have adopted the SMR to A. grandis, being the case of Minas Gerais (eight municipalities), São Paulo (eight municipalities), Goiás (11 municipalities), Rio Grande do Sul (three municipalities), Bahia (one municipality), Paraná (one municipality) and Rio Grande do Norte (two municipalities).

It is necessary for the producer to seek assistance from the State Agency for Plant Health Defense so that production units can export their fruits. In the case of establishing mitigation areas, it is essential to carry out monitoring by determining the MAD index (flies/traps/day) for six months, and for the establishment of a free area, monitoring must be for two years.

For cucurbit fruits, originating from SMR, to be exported, the MAD index must be less than 0,1. If the index is greater than 0,1 and less than or equal to 0,4, exports are prohibited and the control plan begins. However, if the production unit presents a satisfactory control plan and the index is less than 0,1, production can be certified again (Brasil, 2006). If the MAD index is greater than 0,4, the production, coming from the respective production unit (UP), will be prevented from being certified for export in the current harvest.

Once the detection of the pest is confirmed, the Free Area condition will be suspended and the consequent impediment to the certification of shipments for export (Brasil, 2006).

To eradicate the South American cucurbit fly, in ALP, there is a contingency plan which consists of, after detecting the first specimen, installing 30 McPhail traps and cutting 500 cucurbit fruits in the core area (1km²), for the detection of larvae. 50 McPhail traps must also be installed in an area of ​​10km² around the initial nucleus. In the event of a new detection, all fruits in this area must be collected, destroyed or buried 50cm deep. At the point where they were collected, chemical treatment of the soil and applications of toxic baits should be carried out in the area based on food attractant (hydrolyzed protein - 3%) and insecticide. The region's plant health department must evaluate the traps in adjacent areas and transit routes with potential hosts that give access to the pest focus. After these procedures, if a second specimen is not found and no larvae are detected, the traps in the nucleus and the delimitation area will be reduced to ten and 20, respectively, which will be inspected weekly for a period of 160 days or two cycles of insect life (Brazil, 2006).

The control plan for A. grandis, in SMR, requires that whenever the MAD index of the production unit reaches a value greater than 0,1 and less than or equal to 0,4, during the weekly monitoring period, the producer must implement emergency actions to control the pest, passing to use a density of one trap for every two hectares and start chemical control with registered products, until the MAD index returns to a value below 0,1.

Therefore, producers who already export fruits from their UP must be alert to any indication of the occurrence of this pest in their crops or in adjacent areas. Producers who wish to export their production must contact the State Health Surveillance Agency to check whether their property belongs to an ALP. New producers interested in participating in the SMR must, even if their properties are located in already monitored municipalities, carry out official detection and verification surveys on cucurbit crops for a minimum and uninterrupted period of six months. Otherwise, the producer may request the state to implement an ALP or SMR in their region, with the aim of detecting and managing the risk of the South American cucurbit fly, in addition to maintaining it at population levels required for export. .

Cucurbits in Brazil

Cucurbits constitute an important family of plants used in human food. There are approximately 26 cultivated species, the main crops being: watermelon (Citrullus lanatus), melon (Cucumis melo), cucumber (Cucumis sativus) and pumpkins (Cucurbita spp.). In Brazil, these crops acquire even greater importance, as they are produced by small farmers, who use family labor and thus are important sources for the social and economic development of a region.

Among the main cucurbits produced in Brazil, the Northeast region stands out for the production of watermelon (740 thousand tons (t) and melon (380 thousand t). The South region is the second largest producer of watermelon (590 thousand tons) and melon (20 thousand t) (Agrianual, 2012) In the production of species of the genus Cucurbita spp. (pumpkins, zucchini, pumpkins) the main producing region is the Southeast (204 thousand t), followed by the Northeast region (92 thousand t). The Southeast region also stands out in the production of cucumber (113 thousand t) and chayote (147 thousand t) (IBGE, 2006). The state of Rio Grande do Sul is the largest producer of watermelons in Brazil and also produces practically all cucurbits that are sold for local consumption.