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The order Hymenoptera includes insect groups with the most sophisticated reproduction biology: ants, wasps and bees. These insects build nests, containing brood chambers, or cells, which (wasps) or pollen (bees) for consumption by the offspring. Afterwards, the nest cavity may be closed by an external plug. The nest diaphragms and plug are built of debris, mud, wood dust, macerated leaf mass or entire pieces of leaves, or excreta of the wasp or bee female, such as silk or similar materials. Many wasp species are important mesofaunal predators, controlling populations of some phytophagous insects, for instance, leaf-rolling caterpillars, chemically protected larvae of some leaf beetles and weevils, not consumed by the other predators. Bees are one of the main pollinators of the entomophilous plants, considered a keystone insect group in most ecosystems. Due to the complicated brood care and, as a consequence, relatively low reproduction rate, as well as specialised trophic links, wasps and bees are considered to be sensitive to ecosystem changes. Evaluation of the abundance and species diversity of these insects may provide information on the state of the assessed ecosystem (Tscharntke et al. 1998, Gayubo et al. 2005). The cavity-nesting wasps and bees readily occupy various simple artificial trap-nests, made of drilled wooden blocks, paper or plastic tubes, or bundles of internodes of reed or bamboo stems. Trap-nests of standardised construction are used as simple field method to assess the abundance and diversity of the cavity-nesting wasp and bee community. In the study sites, the trap-nests are usually exposed for the whole …