Cherry fly: A new threat to Brazilian fruit growing

Drosophila suzukii detected in Rio Grande do Sul and Santa Catarina

10.11.2015 | 21:59 (UTC -3)

Cherry fly: A new threat to Brazilian fruit growing

Daniele Cristine Hoffmann Schlesener1, Adrise Medeiro Nunes2, Juliana Cordeiro3, Marco Silva Gottschalk3 Flávio Roberto Mello Garcia1,2

(1) Postgraduate Program in Plant Health, Federal University of Pelotas (UFPel), (mity_dani@yahoo.com.br).

(2) Postgraduate Program in Entomology, UFPel.

(3) Department of Ecology, Zoology and Genetics, Institute of Biology, UFPel.

Worldwide, fruit flies are the main pests of fruit crops. Most of the species that make up this group belong to the Tephritidae family, however in 2013 a species belonging to the Drosophilidae family was detected in Brazil that causes similar damage to fruits with fragile skins. It is Drosophila suzukii (Matsumura, 1931), also known as cherry fly in Asia or spotted wing fly in the United States. This species has been causing severe damage to small fruits in several parts of the world. Similar to the damage caused by tephritids, this fly is capable of laying eggs inside fruits, differing from other drosophilids, which are commonly associated with previously damaged or decomposing fruits.

The first record of D. suzukii was made by Matsumura in 1931 in Japan, where it is believed to be its place of origin. Since 2008, it has been causing a series of damages in European and North American countries, quickly dispersing throughout the territory. It was recently found in South America, where it was recorded in municipalities in Rio Grande do Sul, such as Erechim, Vila Maria, Osório and Capão do Leão, and in cities on the coast of Santa Catarina, Nova Veneza and Botuverá (DEPRÁ et al., 2014) . It is believed that the rapid spread of this pest was caused by passive diffusion of fruits, through the import and export of fruits contaminated with eggs. This form of dispersion is one of the most common means of transporting pests between different regions, since despite product contamination, there are no visible signs of the presence of eggs.

The direct damage caused by this pest is caused as a result of oviposition inside the fruits, and later feeding of the larvae. Furthermore, the laying hole also serves as an entry point for pathogens. Oviposition in intact fruits is only possible because D. suzukii females have a double serrated and narrow ovipositor, with a series of sclerotized teeth, which is a distinctive characteristic of most other drosophilids. Identification of males can be made from dark spots on the apex of the wings and a line of combs on the first and second tarsal segments of the first pair of legs.

This insect has been considered one of the main pests of sensitive-skinned fruits in several countries, as it attacks a wide range of fruits. The fruits attacked by D. suzukii have a thin tegument, which allows the insertion of the female ovipositor. There are records of significant damage to plum trees (Prunus sp.), mulberry trees (Rubus sp.), persimmon trees (Diospyrus kaki), cherry trees (Prunus sp.), apricot trees (Prunus armeniaca), raspberries (Rubus idaeus), blueberries (Vaccinium myrtillus) , strawberry (Fragaria sp.) and peach (Prunus persica), and may occur even in smaller proportions in fig (Ficus sp.), kiwi (Actinidia sp.) and vine (Vitis sp.). These insects have already been found attacking fruits with tougher skins, such as orange trees (Citrus sp.) and apple trees (Malus sp.). In Brazil, there are records of its occurrence in guava (Psidium guajava) and jamelo (Syzygium jambolanum). The importance of studies focused on the bioecology and management of these insects is of paramount importance, given the economic significance of these fruits for South American countries, especially regions with a temperate climate. Among the potential hosts of D. suzukii in Brazil, vines (81.355 ha), apple trees (38.205 ha), peach and plum trees (19.043 ha), persimmon trees (8.638 ha), strawberry trees, mulberry trees, raspberries and blueberries (3.560 ha) stand out. and fig tree (2.886 ha) (FRUIT CULTURE YEARBOOK, 2014).

Regarding oviposition behavior and preference, a higher percentage of ovipositions was found in fruits at an advanced stage of ripening, when compared to green fruits or fruits at the beginning of ripening. This fact may be related to the difficulty of completing its cycle in excessively acidic fruits, with the preference being for sweeter and more mature fruits. Taking into account the oviposition preference on different types of fruits, D. suzukii has a preference for cherries, when compared to peach and plum, with infestation levels being 73%, 20% and 7%, respectively (LEE et al ., 2011).

The eggs are whitish in color and measure approximately 0,62 x 0,18 mm in length, and over time they acquire a translucent appearance, making it possible to visualize the larvae before emergence. The eggs have two filaments in the terminal portion of one of the ends, this structure being used for respiration. The newly emerged larvae are milky and transparent in color. In general, they have 3 larval instars, with the last instar larvae measuring, on average, 3,94 x 0,88mm. The pupae initially have a grayish yellow color and a soft consistency, later they harden and acquire a brown color. These have two extensions on one of the terminal faces, coming from the respiratory filaments of the larvae. The immature stages of Drosophila are all similar, so specific identification depends on the emergence of the adult insect or molecular biology techniques (HAUSER, 2011; WALSH et al., 2011). The adult fly is small, between 2 and 3 mm in size, has red eyes, the thorax is yellow to pale brown, with longitudinal black bands along the abdomen.

Most drosophilid species have high biotic potential, which occurs with D. suzukii. Females reach sexual maturity in 1 or 2 days under favorable temperature and humidity conditions, with the maximum time recorded being 13 days. They begin to lay eggs from the second day after emergence, and can lay up to three eggs per fruit. Each female, on average, lays 7 to 16 eggs per day, being capable of ovipositing up to 600 eggs throughout her life cycle (on average 400 eggs). The maximum oviposition recorded for this species was 160 eggs in just one day, in cherry. Eggs hatch within 2 to 72 hours after oviposition, and larvae reach their last instar within 3 to 13 days. The pupa period generally occurs inside the fruit, and may occasionally occur in the soil, and takes around 3 to 15 days. Temperature is an extremely important factor in measuring the cycle time of D. suzukii, with the minimum time recorded being 8 days, between oviposition and adult emergence, and the estimated average time is 8 to 18 days. The longevity of adults varies between 21 and 66 days.

Cherry flies can withstand large temperature variations, but they are more adapted to mild temperatures, ranging from around 20 to 25°C, preferably with high levels of humidity. This climate scenario is easily found in Temperate Climate regions in Brazil, and in other places in South America. High temperatures can be a limiting factor for this insect, with its biology becoming affected at temperatures above 32°C. At temperatures below 5°C, a phenomenon known as diapause can occur, where insects cease their development, resuming their activity as soon as conditions become favorable again.

Economic Losses

Estimating the costs of losses caused by D. suzukii attacks is an arduous task, due to the difficulty of measuring direct and indirect losses caused by the presence of the pest. Direct losses are linked to a drop in productivity and fruit quality, while indirect losses are linked to an increase in production costs, with an increase in labor, equipment and products for chemical control and monitoring. In Europe, losses of 80% in the production of small fruits were recorded, mainly in areas where the occurrence of the fly was initially neglected. Preliminary studies carried out in the United States indicate that annual losses in five crops (mulberry, cherry, raspberry, blueberry and strawberry) reached more than 500 million dollars, in just three states (California, Oregon and Washington). Losses can be even greater in areas where there is a predominance of monoculture, such as on a 400ha property in the Northeast region of Italy, a large producer of small fruits, where losses reached 500 thousand euros in 2010, and approximately 3 million euros in the following harvest (WALSH et al., 2011; ANFORA, 2012).

Monitoring and control

Several monitoring and control systems have been developed in countries where the presence of this pest is already consolidated. However, most of these systems are not yet well defined. Monitoring has been carried out basically through traps containing attractive bait, distributed throughout the orchards. It is recommended to use three traps per hectare, positioned in ventilated and shaded places. The colors that are most attractive to drosophilids are red and black, and it is preferable to use traps with these colors. The types of traps most used for monitoring the pest are the McPhail type. Cups or even adapted PET bottles can be used, with side holes that allow the insect to enter.

Various attractive substances, such as molasses, vinegar of various types, rice and cherry wine, sugar, essential oils of geranium and citronella, synthetic compounds were tested to monitor D. suzukii, and the bait that showed the best attractiveness was the solution of apple cider vinegar and red wine, in a proportion of 40:60, respectively (LANDOLT et al., 2011). It is important to add a surfactant (detergent) to reduce the surface tension of the liquid, thus preventing insects from escaping.

In countries where this pest is already causing economic damage, the most commonly used control method is chemical control. Organophosphates, pyrethroids, spinosad, chlorantraniliprole and an experimental product (TA2674) showed good results in its control, with spinosad causing mortality in 100% of individuals (CUTHBERTSON et al., 2014). Neonicotinoids and systemic organophosphates have ovicidal action and the ability to control larvae inside the fruits. It is recommended to carry out at least two sprays before harvesting, alternating chemical groups, to avoid the emergence of resistant strains. There are few studies on alternative products, such as those used in organic agriculture. Likewise, the withdrawal period for these insecticides must be respected, since most of these crops have multiple harvests and high perishability.

Combined with chemical control, cultural control is essential for successful management. Cultural control is understood as the removal of host plants that are close to the cultivation area. This task is made difficult due to the high polyphagy presented by D. suzukii and the lack of knowledge about possible and/or potential hosts. It is also recommended to remove fallen and damaged fruits from the orchard, as these can also serve as alternative hosts for their development.

Research points to biological control as a future associative measure with other control methods. Some parasitoid wasps (Hymenoptera) have already been found associated with D. suzukii, but without showing very encouraging results. It is believed that the low parasitism may be associated with the peculiar behavior of this drosophilid, since the eggs and larvae of D. suzukii are protected inside the fruits, compared to those that oviposit and complete their development in damaged and exposed fruits. Another line of research that has been developed is the use of entomopathogenic microorganisms (fungi and nematodes) to control this pest. The preliminary results of these studies demonstrated that these organisms promote a reduction in the D. suzukii population, but their isolated use is not capable of promoting effective control.

Final Words

The simple occurrence of this pest in Rio Grande do Sul and other regions with a temperate climate, combined with the wide availability of food and favorable climatic conditions, are factors that concern producers and researchers. There are several questions about the bioecology of D. suzukii that need to be answered, so that new monitoring and control techniques can be implemented, enabling the Integrated Management of this pest. Seeking to answer some of these questions, the doctoral thesis of the first author of this article is being developed in the Postgraduate Program in Plant Health at UFPel, with the effective participation of researchers from the Department of Ecology, Zoology and Genetics of the University's Institute of Biology Federal of Pelotas.

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