Edge effects of pesticide drift in flower strips: implications for functional biodiversity and landscape design

Abstract: Flower-rich off-crop habitats, such as annual or perennial flower strips, are
implemented in European agricultural landscapes to promote functional biodiversity and
support ecosystem services, like pollination and natural pest control. As refuges for beneficial
arthropods, they are central to agri-environmental schemes. Yet, their proximity to treated crops potentially results in high exposure to pesticides, which may compromise their capacity to deliver the desired ecosystem services.
We conducted a two-year field experiment (2023-2024) in annual flower strips in
Switzerland to assess acute, population and community-level responses of non-target
arthropods (NTAs) to realistic drift deposition of the neonicotinoid insecticide acetamiprid. A
randomized block design compared untreated plots (negative control), plots treated at an
assumed field rate of 40 g a.s./ha (full-rate as positive control), and plots receiving simulated
drift rates of 28 %, 1.2 %, and 0.38 % of the field rate at distances of 0-1 m, 1-3 m, and 3-6 m
from the edge (drift-rate). Arthropods from multiple functional guilds were collected using
sticky traps, pan traps, and suction sampling.
Simulated drift rates of acetamiprid caused significant short-term knockdown effects
within the first meter of the flower strip, particularly, in parasitic Hymenoptera. Effects
decreased with distance, and no persistent population- or community-level changes were
detected over the season when sampling the 6-m width of the flower strip. Nevertheless, the
first meter proved the most vulnerable zone to drift exposure, and its negative impacts may
create a management trade-off. Full-rate applications in the positive control treatment caused clear acute and sustained declines in several taxa, confirming the sensitivity of our multimethod monitoring approach.
Our results suggest that wide flower strips (≥ 6-m) can mitigate local drift impacts.
Integrating drift-exposure gradients into biodiversity risk assessment and agri-environmental
planning will help to ensure that off-crop habitats achieve their intended ecosystem services.