Beneficial insect assemblages in floral strips and comparison fields

We installed thirteen floral strips next to rotationally managed
agricultural fields in 2019 in Manitoba, Canada, and then monitored
beneficial insects on field edges and within fields 1–3 years after
establishment (2019–2022). Treatments included strip (crop fields with a
floral strip located on one edge), control (crop fields with naturally
occurring vegetation on the field edges), and unmanaged natural sites (no
crop or enhancements). We measured ground beetle active density and
Shannon diversity using pitfall traps. Bee and syrphid fly capture rates
and Shannon diversity were measured with net transects, blue vane traps,
and pan traps. We compared insect capture rates and diversities using
Generalized linear mixed effect models and compared insect communities
using permutational analysis of variance within strips in 2020,
but declined to similar levels as control sites in 2021. Though
no effect of treatment was found, bees were more abundant in
strips compared to other treatments. Both bee abundance and
diversity at strip sites increased over time. Syrphid abundance
and diversity were not affected by treatment. Spillover
of bees into adjacent blooming and non-blooming crops was twice
as high in strip fields as in the control comparisons. Although no
differences in spillover were found between treatments for syrphids
or ground beetles. Floral strips increased the abundance
of pollinators within adjacent crops, including blooming canola,
which may lead to increased ecosystem services within crops. Our
research supports the use of floral strips in rotational
agriculture to manage local insect populations.