Graduate Thesis Or Dissertation


Marking, movement, and management of Drosophila suzukii in Oregon berry crops Public Deposited

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  • Drosophila suzukii Matsumura (Diptera: Drosophilidae) are small invasive flies that in the past five years (2009-2014) invaded berry and stone fruit production regions in Europe and the Americas. Evolutionary adaptations, biological traits, and anthropogenic factors have contributed to its current status as a global pest. Females oviposit eggs into ripe fruit. Eggs develop into larvae that feed on fruit interiors, rendering fruit unmarketable. Growers currently prevent infestation by targeting adult D. suzukii with broad-spectrum insecticides multiple times during the harvest season. Aside from environmental and non-target impacts of this intensive management strategy, growers are faced with other challenges, such as fruit knockdown from sprayers, abiding by insecticide restricted entry and preharvest intervals, disrupting current integrated pest management (Southwood and Way 1970) programs, and increased input costs. Pest activity levels and movement were tested in a field mark-capture study with previously evaluated and inexpensive protein markers. Results confirmed high adult D. suzukii activity and movement from surrounding non-crop hosts such as 'Himalaya' blackberry into nearby susceptible raspberry. Systemic markers are another method to test pest ecology hypotheses that protein markers cannot help answer. Albeit more expensive than protein marking, markers such as the trace element, rubidium, and stable isotope, ¹⁵N, are readily absorbed by plants. In a greenhouse study, both markers were detected in adults, from larvae that fed on enriched strawberry fruits; however, ¹⁵N was highly persistent in adults after 14 days compared to the rapidly decaying rubidium. Given D. suzukii's highly mobile nature and propensity to use non-crop areas surrounding susceptible crop as overwintering sites or refugia, reduced insecticide application strategies were tested from 2011-2013. Only the border of crop areas was treated with insecticides while leaving the center untreated. Multiple border sprays during two blueberry harvest seasons were made to create a 'wall of insecticides' and prevent invasion of D. suzukii from surrounding non-crop areas. In addition, alternate row (middle) sprays was tested, where one side of two rows was treated with each sprayer pass. The untreated side of each row is thought to provide a refuge for natural enemies. Subsequent sprays were applied on the previously untreated rows. Multiple raspberry sites were treated with this method during three harvest seasons. These reduced insecticide application methods managed D. suzukii adults and larvae as well as complete field applications (border sprays in a low pressure situation), mitigated grower insecticide application challenges (e.g., application time, fruit knockdown in border sprays depending on grower practice), conserved post-harvest natural enemy populations, and reduced input costs. These methods could be easily integrated into a pest management program if associated risks (e.g., pest pressure) are accounted for.
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