Inter‐assemblage facilitation: the functional diversity of cavity‐producing beetles drives the size diversity of cavity‐nesting bees

Inter‐specific interactions are important drivers and maintainers of biodiversity. Compared to trophic and competitive interactions, the role of non‐trophic facilitation among species has received less attention. Cavity‐nesting bees nest in old beetle borings in dead wood, with restricted diameters corresponding to the body size of the bee species. The aim of this study was to test the hypothesis that the functional diversity of cavity‐producing wood boring beetles ‐ in terms of cavity diameters ‐ drives the size diversity of cavity‐nesting bees. The invertebrate communities were sampled in 30 sites, located in forested landscapes along an elevational gradient. We regressed the species richness and abundance of cavity nesting bees against the species richness and abundance of wood boring beetles, non‐wood boring beetles and elevation. The proportion of cavity nesting bees in bee species assemblage was regressed against the species richness and abundance of wood boring beetles. We also tested the relationships between the size diversity of cavity nesting bees and wood boring beetles. The species richness and abundance of cavity nesting bees increased with the species richness and abundance of wood boring beetles. No such relationship was found for non‐wood boring beetles. The abundance of wood boring beetles was also related to an increased proportion of cavity nesting bee individuals. Moreover, the size diversity of cavity‐nesting bees increased with the functional diversity of wood boring beetles. Specifically, the mean and dispersion of bee body sizes increased with the functional dispersion of large wood boring beetles. The positive relationships between cavity producing bees and cavity nesting bees suggest that non‐trophic facilitative interactions between species assemblages play important roles in organizing bee species assemblages. Considering a community‐wide approach may therefore be required if we are to successfully understand and conserve wild bee species assemblages in forested landscapes

The Male-Produced Aggregation-Sex Pheromone of the Cerambycid Beetle Plagionotus detritus ssp. detritus

The number of longhorn beetles with confirmed aggregation-sex pheromones has increased rapidly in recent years. However, the species that have been studied most intensively are pests, whereas much less is known about the pheromones of longhorn beetles that are rare or threatened. We studied the cerambycid beetle Plagionotus detritus ssp. detritus with the goal of confirming the presence and composition of an aggregation-sex pheromone. This species has suffered widespread population decline due to habitat loss in Western Europe, and it is now considered threatened and near extinction in several countries. Beetles from a captive breeding program in Sweden were used for headspace sampling. Gas chromatography-mass spectrometry revealed that collections from males contained large quantities of two compounds, identified as (R)-3-hydroxy-2-hexanone (major component) and (S)-2-hydroxy-3-octanone (minor component), in addition to smaller quantities of 2,3-hexanedione and 2,3-octanedione. None of the compounds was present in collections from females. When tested singly in a field bioassay, racemic 3-hydroxy-2-hexanone and 2-hydroxy-3-octanone were not attractive to P. detritus, whereas a 5:1 blend elicited significant attraction. Both compounds are known as components of the pheromones of conspecific beetles, but, to our knowledge, this is the first cerambycid shown to use two compounds with different chain lengths, in which the positions of the hydroxyl and carbonyl functions are interchanged between the two. The pheromone has potential as an efficient tool to detect and monitor populations of P. detritus, and may also be useful in more complex studies on the ecology and conservation requirements of this species

Colonisation of ephemeral forest habitats by specialised species: beetles and bugs associated with recently dead aspen wood

The most appropriate strategy for preserving fragmented populations depends on a species’ ability to colonise distant habitat patches. Insects associated with early decay stages of dead wood are expected to have a high capacity to colonise new habitat patches. To study the dispersal ranges of beetles (Coleoptera) and flat bugs (Hemiptera: Aradidae) dependent on recently dead aspen (Populus tremula) wood in Finland, we set out 58 piles of recently cut aspen logs at various distances up to 1.6 km from forests that contained a high density of old aspen trees. We captured insects by trunk window-traps, and counted beetles’ exit holes. Habitat connectivity was measured in terms of the amount of suitable aspen-wood in the surrounding environment, with the closest dead wood items up-weighted by a negative-exponential function. The log-piles attracted many saproxylic insects including four red-listed aspen-specialist species. The exposure of log-piles to the sun, and high levels of habitat connectivity increased the species richness of aspen-specialists, whereas bark peeling by moose decreased richness. The spatial scale at which species richness had its strongest response to habitat was 93 m. Among individual species there was a wide variability in spatial scale of response. This study supports the view that conservation efforts in boreal forests should be concentrated on sites where colonisation by target species is most likely. Restoration of habitat by re-locating logs may be useful at localities with a rich and specialised fauna but which have too low rate of formation of dead wood by natural processes