Effects of non-crop habitat on Drosophila suzukii infestation in commercial blackberry fields in North Carolina

Drosophila suzukii (Matsumura), the spotted wing drosophila, is one of several invasive species that have devastated integrated pest management programs in the United States in recent years. Monitoring programs for D. suzukii that reliably predict infestation risk for growers are not currently available. However, it has been suggested that non-crop habitat may serve as a source of infesting populations and provide D. suzukii with refuge from management treatments. The objective of this research was to determine if proximity to non-crop habitat affects fruit infestation levels in crop fields. The hypothesis that infestation rates will decrease as distance from non-crop habitat increases was tested in 2013 and 2014 at commercial blackberry farms in western North Carolina. Infestation levels were measured weekly along transects that ran from 1) a wooded edge and 2) a water source into crop fields at each farm. Standard D. suzukii traps baited with a yeast/sugar/water solution were placed at regular intervals along each transect. Larval infestation was measured in samples of 40 ripe, marketable-looking berries collected near each trap placed within a crop field. After infestation was detected, more females were caught in traps placed outside of crop fields than in traps placed within crop fields. There was no obvious pattern to initial infestation  and proximity to non-crop habitat did not fully explain infestation patterns. Understanding the population dynamics of D. suzukii and the importance of non-crop habitat will help growers effectively time insecticide applications and is essential for the development of future management strategies.