First record of Drosophila suzukii in Italy: addition to the EPPO Alert List
The NPPO of Italy recently informed the EPPO Secretariat of the first record of Drosophila suzukii (Diptera: Drosophilidae) on its territory. In September 2009, numerous larvae of an unknown drosophilidae were found in ripening raspberries (Rubus idaeus) collected from a field near Pergine Valsugana (province of Trento – Trentino-Alto Adige region) in the northeast of Italy. The insect was identified as D. suzukii, an Asian pest of fruit crops which has recently been found damaging small fruit and fruit tree crops in North America. In Italy following its initial discovery, D. suzukii was detected during the autumn 2009 in a few areas of the province of Trento, in the municipalities of Pergine Valsugana (Canzolino), Trento (Vigo Meano), Imer, Segonzano, and Vigo Cavedine. Damage has been observed on the following crops: Vaccinium spp. (blueberries), Rubus idaeus (raspberries), Fragaria ananassa (strawberries), Rubus spp. (blackberries). It is noted that small fruit crops are economically important in the province of Trento (covering approximately 600 ha, mainly in the eastern valleys of the province), and it is feared that the pest may attack other major fruit crops (e.g. cherries, peaches, nectarines, plums, grapes and apples) in Italy. In Trentino, all fruits from infected crops were collected and destroyed. In 2010, surveys will be intensified to determine the extent of the infestation (inspection of fruit crops, trapping programmes etc.) and fruit growers will be informed of this new pest introduction.
Drosophila suzukii originates from Asia. The species was first described in Japan in 1931 (although its presence was first registered in Yamanashi Prefecture, Honshu, in 1916). In Japan, D. suzukii is reported to cause damage to several fruits crops (including cherries and blueberries). In the USA, the presence of D. suzukii has been reported in Hawaii since the 1980s, but apparently without any particular damage to fruit crops. In continental USA, unusual damage caused by a drosophila fly was first observed in September 2008 in a raspberry field in Santa Cruz County, California (US). At first, the pest was misidentified as D. biarmipes but with additional samples being collected from other locations in Santa Cruz County and cherry growing areas of the Central Valley, the identity of the pest could be confirmed as D. suzukii. At the end of 2009, the insect was considered to be established in many Californian counties. During 2009, D. suzukii spread to other US states (Florida, Oregon and Washington) and to British Columbia in Canada (Fraser and Central Okanagan Valleys).
Because D. suzukii is currently spreading and causing damage to fruit crops in North America, and has also been introduced into Europe, the EPPO Secretariat decided to add it to the EPPO Alert List.
Drosophila suzukii (Diptera: Drosophilidae – spotted wing drosophila)
Why: Drosophila suzukii is an Asian pest of fruit crops which has almost simultaneously been introduced into North America and in Italy (in 2008 and 2009, respectively). Because the pest has a high potential for spread and can cause economic damage to many fruit crops, the EPPO Secretariat decided to add D. suzukii to the Alert List.
EPPO region: Italy (province of Trento - Trentino-Alto Adige region), Russia (Far East).
Note: Hauser et al. (2009) mention that D. suzukii has been found in October 2008 in Spain near Barcelona. The EPPO Secretariat is currently verifying this information. In their paper, it was also mentioned that unconfirmed records had been made from Montpellier and the Alps in France, but the French NPPO confirmed that D. suzukii has not been reported from its territory and that no specimens have ever been sent to their official laboratories for identification.
North America: Canada (British Columbia, first found in autumn 2009 in the Fraser Valley area and caught in a cherry orchard in the Central Okanagan Valley), USA (Hawaii introduced into the 1980s; California (2008), Oregon (2009), Washington (2009)).
On which plants: D. suzukii has a wide host range and can attack many fruit crops, including small fruit crops, fruit trees and grapevine. Its host range includes: Actinidia spp. (kiwis), Diospyros kaki (persimmons), Ficus carica (figs), Fragaria ananassa (strawberries), Malus domestica (apples), Prunus avium (sweet cherries), P. domestica (plums), P. persica (peaches), Pyrus pyrifolia (Asian pears), Rubus armeniacus (Himalayan blackberries), R. loganobaccus (loganberries), R. idaeus (raspberries), R. laciniatus (evergreen blackberries), R. ursinus (marionberries), and other blackberries (Rubus spp.), Vaccinium spp. (blueberries), Vitis vinifera (table and wine grapes).
Damage: Although the vast majority of Drosophila species are not fruit pests (larvae developing only in damaged or rotting fruits), D. suzukii is one of the very few Drosophila species which are able to feed on healthy ripening fruit while they are still attached to the plant. Damage is caused by larvae feeding on fruit pulp inside the fruit and berries. Very rapidly, infested fruit begin to collapse around the feeding site. Thereafter, secondary fungal or bacterial infections may contribute to further fruit deterioration (i.e. rotting). In the USA, severe losses have been reported in cherry production in California (estimated at 25% state-wide in 2009). Several berry growers in California, Oregon and Washington, and peach growers from Oregon have reported up to 100% crop losses in some fields.
Adults are brownish yellow flies with black bands on the abdomen, and bright red eyes. Males (2.6 - 2.8 mm long) have a dark spot along the front edge of each wing (hence its English common name), and two rows of combs on each fore tarsus. Females (3.2 - 3.4 mm long) do not have spots on their wings, nor tarsal combs. On average, females can lay 1 to 3 eggs at each oviposition puncture (and more than 300 eggs in their lifetime), but as many females may visit the same piece of fruit up to 60-70 insects may emerge from a single fruit. Larvae (up to 3.5 mm) have white cylindrical bodies, tapered in their anterior part with elevated posterior spiracles. There are three larval instars before pupation takes place. Pupae (2-3 mm long) are reddish brown with two small projections at the end, and can be inside or outside the fruit.
Pictures can be viewed on the Internet:
Reproduction in Drosophila species is particularly rapid with a short life cycle of 1 to 2 weeks depending of the climatic conditions, therefore a single pair of flies can produce hundreds of offspring within a couple of weeks. In Japan, D. suzukii has about 13 generations per year, and predictions made for the Californian climate are of 3 to 10 generations per year. D. suzukii seems to prefer high humidity and moderate temperatures. Cold winters do not seem to limit the insect’s survival, considering its establishment in Northern China and the Southern part of Hokkaido (Japan).
Dissemination: Adults are highly mobile. The rapid spread which is currently being observed in North America demonstrates the high capacity of this insect for natural spread. Over long distances, trade of infested fruit and plants can ensure pest dissemination. For the moment, it is not known how D. suzukii was introduced into North America and Europe.
Pathway: Plants of planting, fruit of D. suzukii host plants.
Possible risks: Many host plants of D. suzukii (e.g. Fragaria, Prunus, Rubus, Vaccinium, Vitis vinifera) are economically important crops across the EPPO region. The high reproduction rate and capacity for natural spread probably render containment or eradication very difficult. In addition, early infestations are difficult to detect (small oviposition scars) and these infested fruit are likely to be traded undetected. For the moment, data is lacking on the potential of establishment of D. suzukii in the EPPO region, but the fact that D. suzukii seems to favour cool and humid climate (e.g. in central coastal California) suggests that it probably has the potential to establish in most parts of the EPPO region. Preliminary results from Climex/Maxent modelling studies (done for North America only) showed that D. suzukii has the potential to establish along the west coast of USA and Canada (e.g. British Columbia), and in large parts of Eastern USA. For the moment, data is lacking about field (e.g. ‘attract-and-kill strategy’) and post-harvest treatments (e.g. cold treatments, fumigation, irradiation) but investigations are being initiated in the USA. It is considered that sanitation techniques (fruit removal, pruning) could help to reduce pest populations. There is no data on biological control but it is mentioned in the Japanese literature that larvae of D. suzukii were naturally parasitized by a species belonging to the genus Phaenopria (Hymenoptera: Diapriidae). Although data is lacking about the insect biology and its economic impact, preliminary observations made in countries where the pest has been introduced, suggest that D. suzukii is a serious threat to many fruit crops in the EPPO region.
EPPO RS 2010/007
Panel review date: -
Entry date 2010-01
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