Factors influencing host fruit preference and cultural management of Drosophila suzukii (Matsumura)

Drosophila suzukii (Matsumura), an invasive pest from East Asia, is threatening the U.S. small fruit industry. A study was conducted to understand how firmness affects D. suzukii host suitability and preference. Firmness was measured for 100 fully-ripe rabbiteye blueberries (Vaccinium virgatum Aiton) from 3 cultivars. For the no-choice tests, 20-g samples of fully-ripe blueberries of each cultivar were placed in plastic containers (15 replicates). For choice tests, 20-g samples of all cultivars (3) and blue clay balls (control) were placed into a plastic container (12 replicates). Berries were exposed to 10 male and female flies for 4 h. After fly removal, eggs were counted using visible egg filaments. Oneway ANOVA was used to analyze differences in eggs laid among cultivars and regression analysis was used to correlate the number of eggs to firmness. Another study was conducted in organic blackberries (Prunus spp. var. Natchez) to determine whether border sprays and between-row cultivation would suppress D. suzukii populations. Blackberries were in two plantings separated by a 6.1-m-wide road. Both plantings received an initial application of Entrust® (spinosad). One planting received a border spray of Azera® (azadirachtin + pyrethrins). The border spray was repeated after 7 d. Between-rows were cultivated to remove weeds in half of each planting. Adult D. suzukii were sampled weekly using clear plastic cup traps baited with yeast sugar water. Results from the berry bioassays showed differences in firmness but not in suitability or preference of cultivars. The border spray study suggests that between-row cultivation may be an effective strategy for suppressing D. suzukii in organic fruit crops.