In this study our aim was to assess the diversity and distribution of
cavity-nesting solitary bees, wasps and the spider-hunting wasps' prey
with regards to the influence of landscape context in a study area with
relatively low human disturbance. The study took place between May and
August 2018 at eight study sites in the hilly-mountainous central part
of Romania, where the majority of the landscape is used for extensive
farming or forestry. During the processing of the trap nest material, we
recorded several parameters regarding the nests of different
hymenopteran groups, the spider prey found inside these nests, and also
tested the influence of the landscape structure surrounding the sites on
both hymenopteran groups and spider prey. The majority of nests was
built by the solitary wasp group of Trypoxylon, followed by Dipogon and
Eumeninae. Solitary bees were much rarer, with Hylaeus being most common
group. The groups showed partially differing size preferences concerning
the diameter of the occupied reed stalks. In the nests of Trypoxylon we
predominantly found spider prey from the family of Araneidae, followed
by representatives from the families of Linyphiidae and Theridiidae. In
contrast to Trypoxylon, the wasp group Dipogon preferred spider prey
from the family of Thomisidae. Concerning the hymenopteran groups,
significant effects of landscape structure were found on the number of
both nests and brood cells of Eumeninae and on the number of brood cells
of Hylaeus, Osmia and Trypoxylon. We also found that the diversity of
Trypoxylon spider prey was significantly positively affected by an
increasing proportion of grassland and negatively by an increasing
proportion of woodland. Altogether, our study presents several new
aspects concerning the diversity and distribution of solitary bees,
wasps and the spider-hunting wasps' prey and also the effects of
landscape context on these groups.