Inês I. Vicente

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.

Insect habitat specialists have declined more than generalists over the last decades. Understanding how habitat requirements and increased climate variability interact to explain persistence of populations is needed to enable effective conservation measures. Habitat specialists with a complex life cycle, such as myrmecophilous butterflies, are likely to be most vulnerable. Here, we explored to what extent the habitat factors explaining population persistence of the Alcon blue (Phengaris alcon), changed over a 25-year period in the Netherlands, contrasting the recent years 2018–2022 with extreme droughts with the preceding period 1998–2017 characterized by occasional climatic extremes. Population persistence of P. alcon over 1998–2017 as explained by historical habitat conditions was significantly higher in large heathland areas with large patches of its host plant Gentiana pneumonanthe. On the basis of current conditions, population persistence until 2017 was best explained by a combination of host plant area and quality. In contrast, persistence over the recent drought years was most closely associated with increasing occupancy of the optimal host ant Myrmica ruginodis and lower occupancy of competitive and predatory Lasius ants.Implications for insect conservation We conclude that critical habitat conditions change under increasing climatic extremes and that the availability of sufficient optimal host ants has become more critical than that of host plants. The results emphasise that both large-scale hydrological restoration and small-scale management for heterogeneity are necessary to preserve P. alcon and its habitat in the Netherlands. This is also likely to apply to other habitat specialists with complex life cycles from threatened habitats.