Spotted wing Drosophila (Drosophila suzukii), or SWD, a fruit fly native to East Asia, has become pervasive on fruit farms across North America in the past decade, laying its eggs inside thin-skinned fruits. It’s short generation time, release from native predators, and modified, serrated ovipositor make infestation rates difficult to control. Many tart cherry growers in Michigan combat increasing populations with broad spectrum pesticides like pyrethroids and organophosphates, risking increased pesticide resistance and declines in populations of natural enemies of SWD. In response to these threats, cherry growers have applied cultural management practices (CMPs) and considered supporting native and introduced parasitoids in their integrated pest management programs to more effectively control SWD infestation.
Our research evaluated the effect of four cultural management treatments (factorial combinations of mowing and pruning) on SWD, parasitoids (Hymenoptera), and predator abundance and diversity in the trees and grasses of four Montmorency tart cherry orchards in West Central Michigan. We vacuum-sampled arthropod communities twice before harvest when cherries were susceptible to SWD infestation and once three weeks after harvest to assess community dynamics throughout the growing season. We also performed semi-structured interviews with Michigan tart cherry growers to gauge their responses to SWD and feelings about available pest management strategies.
Results/Conclusions
We found no difference in SWD or parasitoid abundances between the cultural management treatments across sampling events. SWD and parasitoid abundances peaked at opposite times in relation to the day of harvest, suggesting potential phenological mismatches between the two groups. Overall abundance of SWD was low for the season compared to previous years, likely due to significant drops in temperature over the 2017-2018 winter season, killing populations of overwintering adults.
These results were comparable to growers’ perceptions of the efficacy of CMPs. Growers generally saw CMPs as supplementary to chemical sprays but without potential to replace or reduce spraying. Alternatively, careful preparation by growers after colder winters may allow for increased diversification of management practices, supporting native natural enemy populations while reducing SWD abundance and ensuring a high-quality crop.