Mass-flowering lupin has positive, but limited, effect on wild bee conservation in agricultural landscapes

Mass-flowering crops have the potential to benefit pollinator conservation while still contributing to agricultural production, but their effects on pollinators can be variable and remain uncertain. Lupin could be particularly suitable for pollinator conservation because it is a late-flowering legume crop, but its effects on pollinators have never been investigated. We tested the intra- and interannual effects of lupin cultivation on wild bees in landscapes with no history of lupin cultivation. To do this, we surveyed bees in semi-natural habitats before, during, and after lupin bloom and in the following year in landscapes with and without the experimental addition of 1 ha of lupin (Lupinus albus or Lupinus angustifolius). We also surveyed bees within lupin fields during bloom to understand which species use lupin floral resources. We found positive effects of lupin cultivation on the abundance of bumblebees in the wider landscape after lupin bloom, likely due to increased bumblebee colony growth. However, this was only the case for the three common species that used lupin floral resources. In addition, this effect did not carry over into the following year. Some large-bodied solitary bees, namely, Megachile spp., also utilized lupin floral resources but were not numerous enough in the surrounding landscape to determine an effect. This could be due to a general lack of large-flowered leguminous floral resources in agricultural landscapes. Synthesis and applications. Our results indicate that lupin can potentially support the few common, abundant bee species that preferentially visit it. However, to effectively support the entire bee community, conservation management should focus on improving the quality of existing semi-natural habitats by increasing floral availability and diversity, possibly of Fabaceae floral resources in particular.