Authors: Segre, Hila; Kleijn, David;Bartomeus, Ignasi;WallisDeVries, Michiel;Fijen, Thijs;

Monitoring population trends is essential for conservation, but long-term high-intensity monitoring is required to reliably calculate trends. Consequently, we have poor understanding of insect population trends, except for butterflies. Butterfly diversity is considered indicative for other pollinators’ diversity such as bees or hoverflies, but this has never been tested. We sampled 42 of the Dutch butterfly association monitoring sites during April-August 2020 and recorded species richness and abundance of butterflies, bees and hoverflies, and flower cover and richness. Using the same methods we sampled one site in Spain for six years. To test whether pollinators with similar functional traits show similar trends, we categorized bees and butterflies according to their diet breadth, larval resources nitrogen-affinity and body size. Only hoverfly richness was correlated with both butterflies (R² = 0.05) and bees (R² = 0.14), and may be more suitable as a bioindicator of pollinator diversity. Abundance of all three groups showed no significant correlation, except for non-polyphagous species. Despite the weak correlation among pollinators, all groups were highly affected by flower richness, yet, they respond to different host plant families. Monitoring schemes aiming at pollinator conservation should also monitor habitat quality and vegetation resources as bioindicators for multi-taxa pollinator diversity.