Habitat requirements of wetland bees and wasps: several reed-associated species still rely on peaty meadows and other increasingly rare wetland habitats

Reed beds are wetland habitats with the dominance of Phragmites australis, which are inhabited by diverse communities of organisms of high conservation value, known to be good diagnostic species for conservation measures. We studied bees and wasps associated with ten reed bed types and with the galls of frit flies of the genus Lipara in hundreds of localities in central Europe between the years 2011 and 2017. Species assemblages differ among specific types of reed beds; these differences are prominent compared between the near-natural and anthropogenic sites. Species of high conservation value prefer wet meadows with flowering plants and a portion of common reed, or terrestrial reed beds near fishponds, rivers and streams. Similar species also inhabit temporary field wetlands. Reed beds in sand pits, quarries, enduro tracks, brown coal spoil heaps or power plant tailing ponds are inhabited by generalist species. Mowing, the most frequently used management tool for removing common reed, has a positive effect on species nesting in reed stalks but negative on those nesting in reed galls. It is thus necessary to implement mowing only of a part of the reed bed into the management tools and to leave some parts of the reed bed, as well as reed margins, untouched. A high number of small to large reed beds increases the biodiversity of bees, wasps and other invertebrates, and these habitats can serve as biodiversity hotspots in increasingly anthropized and agricultural landscapes.