Spotted wing drosophila: distribution of populations over time in wild and crop hosts

Abstract

Spotted wing drosophila (SWD) was first confirmed in NY at some eastern Long Island farms in 2011. Fruit flies typically attack rotting fruits; SWD, however, feeds in intact fruits. Soft-skinned fruits such as berries are at greatest risk; some stone fruits are also reported among the preferred hosts. Season-long SWD monitoring and fruit damage assessments were done in cultivated crops and in wild fruits growing nearby. A total of 31 apple cider vinegar-baited translucent delicatessen cup monitoring traps were placed in raspberry, peach, blueberry, grape, and apple farms and in adjacent forest areas. The first sustained SWD capture on Long Island occurred on June 9, 2012 at 1320 DD (50oF base temperature). At least two peak SWD activity periods were observed on Long Island: the 1st around September 18 at 2313 DD and the 2nd around October 23 at 3073 DD. The proportion of male:female in trapped populations was observed to be around 50:50. Late-season (September – October) SWD populations appeared to be higher in forest than cultivated areas. Approximately 17 types of cultivated and wild fruits were checked for the presence of SWD eggs or larvae. Pokeweed berries are the most preferred wild host of SWD. Among the other possible wild hosts checked- autumn olive, bittersweet nightshade, European yew berries are the newly detected hosts of SWD grown near cultivated areas. Raspberries and blackberries were most heavily infested by SWD, averaging 73.5% and 77.0% respectively in 2012. Blueberries were less affected (6%) possibly because the local blueberry season typically ends by late July to early August after which SWD populations sharply increased. Very few SWD adults emerged from grape samples and SWD egg-laying in grapes was minimal and only the late-season 'Merlot' and 'Cabernet' varieties were affected. It appears grapes are not a favored host and may not need preventive treatment. Late-season caneberries appear highly susceptible to infestation and most likely require preventive insecticide treatments but growers have little information on specific timing of applications. Information developed from this study advances our understanding of the seasonal abundance, peak appearance, host utilization, and overwintering emergence patterns of SWD. Further research on hosts, overwintering sites, population assessment, baits and control techniques are necessary to help growers contend with this new invasive pest