Title: Odour signals relevant to beetles in deadwood habitats - odorants, olfaction and behaviour.
Abstract: The overall objective of this work was to evaluate and determine volatile chemical cues (infochemicals) that determine insect-wood interactions. The deadwood habitat comprises species that reproduce and spend obligatory most of their lifespan in any kind of wood and in any kind of decay stage, including fungi that depend on wood. A gas chromatograph with mass spectrometric-electroantennographic detection (GC-MS/EAD) has been introduced to define sources of volatiles and identify infochemicals, in particular host produced kairomones, but also allomones and pheromones relevant to selected beetle species of an either xylophagous, mycophagous or xylomycetophagous feeding type respectively. Complex chemical profiles of wood, deadwood and fungal samples have been analysed. Half of thirty compounds identified in the headspace of dry pine timber, the most artificial kind of deadwood, elicited responses in antennae of the Old House Borer Hylotrupes bajulus, a major pest of structural softwood. Aliphatic aldehydes, which are however not specific to the host tree species, are proposed as potential infochemicals and complement the number of terpenoid host kairomones previously known for this xylophagous species. Experiments with felled beech trunks demonstrated that volatile chemistry changes over time and that decay over the length of trunks is quite variable. Potential host kairomones, such as branched alcohols, aldehydes and phenolics have been determined for the fungus farming ambrosia beetle Trypodendron domesticum. They provide a good basis for applications in integrated pest management and risk assessment of this secondary scolytine bark beetle. It attacks occasionally apparently healthy trees and is indicative for a recent emergence of pathogenicity in insect-fungus symbioses. Antennae of the lymexylid Elateroides dermestoides, also xylomycetophagous, were tested for response to volatile compounds emitted from a diverse set of infested host trees including hard- and softwoods. Tree species differed substantially in emitted compounds, but beetles perceived those compounds prevalent from all species, explaining the broad host tree range of the beetle. Most of these compounds emanate from basal fungal metabolism, as it could be demonstrated by analysing isolated strains of beetle-associated fungi. Perception of yeastlike and filamentous fungi by the beetle, and even more its capability to recognise the major fungal cultivar A. hylecoeti, which is distinguished by a species specific secondary metabolite, have been clearly demonstrated. However, the importance of predominant ubiquitous fungal volatiles for host recognition has been emphasized. Accordingly, future research should pay more attention to the function of volatile infochemicals within symbio! tic relationships and insect-fungus interactions. Fruiting bodies of polypores are common in the deadwood habitat and their colonisers typically decrease in specialisation degree with advancing maturity. Volatiles of fruiting bodies of the bracket fungus Fomes fomentarius were analysed and shown to quantitatively change with maturity in emission of ubiquitous eight-carbon volatiles. They act differentially as infochemicals and control behaviour of the mycophagous specialist Bolitophagus reticulatus. The available literature on eight carbon volatiles from mushrooms and their impact on insects is discussed. They are fungal oxylipins and possibly of comparable importance to mycophagous and saproxylic insects as plant oxylipins like the green leaf volatiles (GLV) are to herbivores. Beside the aforementioned, this is the most apparent case of host recognition with ubiquitous volatiles rather than species specific volatiles. This has been demonstrated multitudinously for herbivores and the studies presented here give reason to apply this idea to the deadwood habitat, and to conclude that host recognition in deadwood habitats occurs by using host (species) specific compounds, but even more by the use of ubiquitous host volatiles pertinent to many wood or fungal species. Beyond such chemical parsimony of host kairomones, further multifunctionality of infochemicals has been demonstrated by attributing a pheromonal function to the defensive secretion of B. reticulatus. Species specific phenolic compounds released by both sexes have been defined that attract only male beetles, which are also more sensitive. They represent the first pheromone demonstrated in Bolitophagini. Findings are placed within the context of insect chemoecology, deadwood ecology and symbiosis research, but are also applicable to integrated pest management, wood technology and wood assessment. Modern analytical instruments and examination of comparably well studied insect species revealed that applying Chemical Ecology in basic research of deadwood is a promising task, giving valuable insights in general principles, efficient across the plant, fungal and insect kingdom.