1. Intensification of agriculture has resulted in a simplification and fragmentation
of agroecosystems. Yet, its impact on the reproductive success and population
dynamics of wild bees, and how adverse effects can be mitigated, remains poorly
understood.
2. We established populations of seven solitary bee species varying in body size in
experimentally sown wildflower strips (WFS), existing semi-natural habitats (SNH;
forest edges) and isolated sites lacking WFS and SNH in the local surrounding
(350 m radius) to test (a) whether the wild bee species use planted flowers of WFS
to provision offspring with pollen, (b) whether vicinity to WFS reduces their foraging
trip duration, (c) parasitism rate and (d) whether it increases bee reproductive
success of nesting populations. Furthermore, we tested whether the effect size
depends on the body size of the bee species considered.
3. We show that wild bees nesting in WFS provisioned their offspring primarily with
pollen from plants of WFS. This led to shorter foraging trips of all bee species
nesting in WFS compared to bees nesting in isolated (unrestored) sites and overall
increased reproductive success (i.e. more viable offspring). Reproductive success
of bees nesting in WFS was also higher, and parasitism rates lower, compared to
bees nesting at forest edges. Smaller—potentially less mobile—bee species benefitted
more than larger ones from WFS plantings in terms of reproductive success.
4. Synthesis and applications. Our findings demonstrate that diverse WFS can enhance
the reproductive success of multiple solitary wild bee species, thereby
mitigating negative impacts of agroecosystem simplification through the provision
of suitable floral resources and reduced foraging times required for offspring
provisioning. Our study further indicates that a relatively fine-meshed network of
wildflower plantings and nesting habitats is required to most effectively enhance
reproduction and populations of solitary bees in agricultural landscapes.