Integrating Alternative SWD Management Practices

Native to Southeast Asia, the spotted wing drosophila (SWD), Drosophila suzukii, is a new invasive insect pest in the USA causing an increasing amount of damage to soft-skinned fruit crops such as blueberries, cherries, raspberries and strawberries. Unlike most other drosophilid species, SWD attacks ripening fruit. Current management programs rely heavily on chemical control. Therefore, other control methods such as cultural and behaviorally-based strategies need to be evaluated. In blueberry farms, harvesting is done by hand or machine. During harvesting operations, many berries fall to the ground and may serve as alternate oviposition sites for gravid SWD females when not enough berries remain on the bush. Removing or destroying potential sources of SWD infestation could reduce their population on farms. In field studies, we investigated SWD preference for berries on bushes versus those on the ground. Our results showed that SWD infestation was higher in berries on bushes than those on the ground. However, SWD adult emergence from fallen berries increased as the season progressed.  We also investigated whether burying infested fruit reduces SWD adult emergence from the soil. We exposed freshly harvested blueberries to 5-6 day old, gravid SWD females for 72 h in an incubator chamber. The berries were then buried under sand at depths of 0, 5, 10, 20, and 30 cm in plastic tubes for 7, 10 and 14 days. The results showed that burying SWD-infested berries below 5, 10, 20, and 30 cm of sand reduces adult emergence by 78, 88, 95, and 100%, respectively. Our results indicate that burying SWD-infested berries may reduce, but not always eliminate, the number of flies emerging from fallen berries. In order to develop effective fruit-based attractants for SWD, we extracted juices from blueberry, cherry, raspberry and strawberry and tested their attractiveness to SWD in olfactometer studies. The results showed that all of the fruit juices are attractive to SWD; however, those from raspberry and strawberry were most attractive. The headspace volatiles from these juices were tested in GC-EAD experiments using antennae from both male and female SWD. Strong electrophysiological antennal responses were observed. The EAG active volatile compounds from raspberries have been identified and their attractiveness will be evaluated under field conditions. SWD attractants could be used in baits for early detection of fruit infestation as well as in the development of attract-and-kill strategies to manage SWD in small fruit farms.