|Abstract or Summary
- 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.