2017 Field Collections
We visited four locations in North Carolina where large wild blackberry
stands (>15 canes/10m) were established: Southern Nantahala
Forest in Macon County; Cherokee National Forest in Avery County, and
Joyce Kilmer –Slickrock Wilderness Area (JKWA) and along the Cherohala
Skyway in Graham County (Supplementary Table S1). Required permits to
sample in these places were obtained from the appropriate agencies.
Sampling sites were determined by location and density of blackberry
plants and separated by a distance of at least 1 km. Fruit collection
began when fruit appeared almost full size (subjectively determined by
drupelet size) but were still green. Sites were resampled every 2-3
weeks until no ripe fruit were available.
At each site, blackberry plants within a radius of 10 m were sampled for
fruit at the following ripeness stages: green, blush (reddish green),
red, purple, and ripe. Two research station plantings of cultivated
blackberries were sampled during the same week as wild collections, but
only ripe fruit were collected at research farms after the first visit
due to low fruit set that year. Up to 20 fruit of each stage were
sampled at each site as available, grouped in breathable bags, and
transported to the lab in a cooler (4ºC). Fruits were collectively
weighed by sample group and examined under a dissecting microscope for
the number of D. suzukii eggs laid per berry. Drosophila
suzukii eggs were distinguished from other potential fruit-infesting
flies by observing and counting the number of respiratory filaments per
oviposition site (Hauser et al. 2011). Although Drosophila
melanogaster and D. simulans eggs also possess only two
filaments per egg, we collected fruits before they were susceptible to
oviposition by these two species. Other plant species growing adjacent
to blackberry plants with ripe fruit that appeared susceptible toD. suzukii were collected at random and similarly checked for
infestation. All plant species were identified using Weakley (2006).