Invasive host for invasive pest: when the Asiatic cherry fly (Drosophila suzukii) meets the American black cherry (Prunus serotina) in Europe : WhenD.suzukiimeetsP.serotina

The Janzen-Connell hypothesis proposes that host-specific, distance- and/or density-dependent predators and herbivores maintain high tree diversity in tropical forests. Negative feedback between plant and soil communities could be a more effective mechanism promoting species coexistence because soil pathogens can increase rapidly in the presence of their host, causing conditions unfavourable for local conspecific recruitment. Here we show that a soil pathogen leads to patterns of seedling mortality in a temperate tree (Prunus serotina) as predicted by the Janzen-Connell hypothesis. In the field, the mean distance to parent of seedling cohorts shifted away from maternal trees over a period of 3 years. Seedlings were grown in soil collected 0-5 m or 25-30 m from Prunus trees. Sterilization of soil collected beneath trees improved seedling survival relative to unsterilized soil, whereas sterilization of distant soil did not affect survival. Pythium spp., isolated from roots of dying seedlings and used to inoculate healthy seedlings, decreased survival by 65% relative to controls. Our results provide the most complete evidence that native pathogens influence tree distributions, as predicted by the Janzen-Connell hypothesis, and suggest that similar ecological mechanisms operate in tropical and temperate forests.

The spotted-wing drosophila, Drosophila suzukii Matsumura, is native to Asia and was first detected in the North American mainland and Europe in 2008-2010. Drosophila suzukii is a serious economic pest to stone and small fruits because the female lays eggs within ripening fruit on a plant before harvest, which can lead to crop loss. The aim of this study was to evaluate the susceptibility of blackberries, blueberries, cherries, grapes, raspberries and strawberries to D. suzukii among various ripeness stages and cultivars. In 26 no-choice and choice replicated laboratory cage tests on ripeness stages, fruits were generally susceptible to D. suzukii once fruits started to color. Few D. suzukii developed on green fruit, wine grapes or overripe blueberries. In seven cultivar tests, D. suzukii preferences ranged from no differences to fourfold differences for specific cultivars of blackberries, blueberries, raspberries and wine grapes. As brix levels increased, more eggs were laid or more D. suzukii developed on blackberries, blueberries, cherries, raspberries and strawberries. In a choice test of various fruit types, strawberries, raspberries, blackberries, cherries and blueberries were more susceptible to D. suzukii than green table grapes ('Thompson'). The results suggest that fruits may become susceptible to D. suzukii as they start to turn color, and that specific varieties of grapes and overripe blueberries have low susceptibility to D. suzukii. Copyright © 2011 Society of Chemical Industry.

Drosophila suzukii is an oriental species first reported outside Asia from Hawaii in 1980. The first confirmed records for the continental United States were made in 2008 in California. The identification of this pest is difficult because very few published resources exist. It has since been recorded in Oregon, Washington, British Columbia, Alberta, Manitoba, Ontario, Quebec, Utah, Michigan, Wisconsin, Louisiana, North Carolina, South Carolina and Florida. Males are relatively easy to identify by the black apical wing spots and the single row of combs on the first and second tarsal segment of the fore leg. The male genitalia are also very characteristic and will aid in identifying teneral specimens. Females can be identified by the large ovipositor, which is 6-7 times as long as the diameter of the spermatheca. Immature stages can only be identified by molecular techniques. Although this species has been recorded from many US states and Canadian provinces, it has not been established in all of these places, and the main economic damage is restricted to the western part of North America. With the characters laid out in this paper, it should be possible to identify the pest with high certainty. Copyright © 2011 Society of Chemical Industry.