Assessing the adaptation potential of pest Cultural Management Practices (CMPs) for spotted wing Drosophila on tart cherry orchards in Michigan

Abstract

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. Its short generation time, release from native predators, andmodified, serrated ovipositormake 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 SWDandparasitoids (Hymenoptera) 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 performedsemi-structured interviews with Michigan tart cherry growers to understand their adaptive responses to SWD and feelings about CMPs as behaviors for adapting to the threats of SWD.We found no difference in SWD or parasitoid abundances between the culturalmanagement 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 low efficacy of CMPsas effective methods for reducing SWD abundance. Growers generally sawCMPsas supplementary to chemical sprays but without potential to replace or reduce spraying. Alternatively, many growers recognized the risk of pesticide resistance and regulation that could reduce the efficacy of chemical pesticides, their primary method of response to SWD. Integrating a diversity of pest management practices into current regimens should continue to be explored for its ability to replace chemical pesticide application, support diverse native natural enemy populations, and sustain economically viable agricultural systems now and in the future.