Bernhard Weißbecker

Antennal and Behavioral Responses of Cis boleti to Fungal Odor of Trametes gibbosa

Cis boleti (Coleoptera: Ciidae) preferentially colonizes fungi from the genus Trametes that are known as important wood decomposers. The aim of our research was to investigate if C. boleti uses the chemical volatile composition of its fungal host, Trametes gibbosa, as a key attraction factor. Therefore, the T. gibbosa fruiting body volatiles were analysed by using gas chromatography-mass spectrometry, with parallel electroantennographic detection (GC-MS/EAD) using adults of C. boleti. Furthermore, we examined the behavioral responses of C. boleti to the T. gibbosa volatile compounds. The dominant component of the T. gibbosa fruiting body bouquet was 1-octen-3-ol. Other volatiles, like the aldehydes hexanal, nonanal, and (E,E)-2,4-decadienal and the terpene alpha-bisabolol, were present in minor quantities. 1-Octen-3-ol was released with a ratio of the (R)- and (S)-enantiomers of 93:7, respectively. Electroantennography (EAG) employing C. boleti antennae yielded consistently dominant responses to 1-octen-3-ol. GC-EAD and EAG responses to pure standard compounds showed that C. boleti also perceived other host fungal volatiles. A highly significant attraction to 1-octen-3-ol was observed in behavioral tests. Female beetles were significantly attracted to the (S)-(+)- enantiomer at 10 times lower doses than male beetles. Our finding is the first direct proof that ciid beetles use 1-octen-3-ol as a key cue for host finding.

Cockchafer Larvae Smell Host Root Scents in Soil

In many insect species olfaction is a key sensory modality. However, examination of the chemical ecology of insects has focussed up to now on insects living above ground. Evidence for behavioral responses to chemical cues in the soil other than CO2 is scarce and the role played by olfaction in the process of finding host roots below ground is not yet understood. The question of whether soil-dwelling beetle larvae can smell their host plant roots has been under debate, but proof is as yet lacking that olfactory perception of volatile compounds released by damaged host plants, as is known for insects living above ground, occurs. Here we show that soil-dwelling larvae of Melolontha hippocastani are well equipped for olfactory perception and respond electrophysiologically and behaviorally to volatiles released by damaged host-plant roots. An olfactory apparatus consisting of pore plates at the antennae and about 70 glomeruli as primary olfactory processing units indicates a highly developed olfactory system. Damage induced host plant volatiles released by oak roots such as eucalyptol and anisol are detected by larval antennae down to 5 ppbv in soil air and elicit directed movement of the larvae in natural soil towards the odor source. Our results demonstrate that plant-root volatiles are likely to be perceived by the larval olfactory system and to guide soil-dwelling white grubs through the dark below ground to their host plants. Thus, to find below-ground host plants cockchafer larvae employ mechanisms that are similar to those employed by the adult beetles flying above ground, despite strikingly different physicochemical conditions in the soil.

Odoriferous Defensive stink gland transcriptome to identify novel genes necessary for quinone synthesis in the red flour beetle, Tribolium castaneum.

Chemical defense is one of the most important traits, which endow insects the ability to conquer a most diverse set of ecological environments. Chemical secretions are used for defense against anything from vertebrate or invertebrate predators to prokaryotic or eukaryotic parasites or food competitors. Tenebrionid beetles are especially prolific in this category, producing several varieties of substituted benzoquinone compounds. In order to get a better understanding of the genetic and molecular basis of defensive secretions, we performed RNA sequencing in a newly emerging insect model, the red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae). To detect genes that are highly and specifically expressed in the odoriferous gland tissues that secret defensive chemical compounds, we compared them to a control tissue, the anterior abdomen. 511 genes were identified in different subtraction groups. Of these, 77 genes were functionally analyzed by RNA interference (RNAi) to recognize induced gland alterations morphologically or changes in gland volatiles by gas chromatography-mass spectrometry. 29 genes (38%) presented strong visible phenotypes, while 67 genes (87%) showed alterations of at least one gland content. Three of these genes showing quinone-less (ql) phenotypes – Tcas-ql VTGl; Tcas-ql ARSB; Tcas-ql MRP – were isolated, molecularly characterized, their expression identified in both types of the secretory glandular cells, and their function determined by quantification of all main components after RNAi. In addition, microbe inhibition assays revealed that a quinone-free status is unable to impede bacterial or fungal growth. Phylogenetic analyses of these three genes indicate that they have evolved independently and specifically for chemical defense in beetles.

Ubiquitous eight-carbon volatiles of fungi are infochemicals for a specialist fungivore

Abstract An enormous variety of volatile substances are released in distinctive blends by fungal substrates that should be recognisable for fungivores. Certain compounds dominate in most of the fungal species. Fungal oxylipins as the eight-carbon volatiles are the most prominent. This raises the question whether such are specific enough to qualify as appropriate host cues for a fungivore. We could demonstrate differentiated responses of the fungivorous beetle Bolitophagus reticulatus to eight-carbon volatiles: Nine eight-carbon volatiles were identified with GC–MS from its host fungus Fomes fomentarius. 1-Octen-3-ol, 3-octanone and 3-octanol induced contrasting behaviour of beetles in olfactometer bioassays. Electroantennographic experiments investigating the beetle olfactory sense revealed distinguishable antennal responses. Moreover, their individual release from F. fomentarius fruiting bodies changes not only considerably, but also independently over successive stages of beetle colonisation. Concentrations of attractive and repellent eight-carbon volatiles correlate to frequency of beetles in the field and further substantiate their relevance as host cues. Our results show that a specialist fungivore is able to differentiate the most common eight-carbon volatiles of fungi to assess host quality. Key roles and marked similarities of fungal to plant oxylipins suggest a comparable importance of eight-carbon volatiles to fungivores as green leaf volatiles have to herbivores.

Biosensors on the Basis of Insect Olfaction

Biosensors utilize organic components like proteins, cells, or fragments of organisms within a technical device. By combining technical transducers with a biological sensory unit it is possible to reproduce the capability of natural sensors, which far exceed mere technical solutions in selectivity and sensitivity. For instance, by integrating the antenna of a Colorado potato beetle (Leptinotarsa decemlineata) in the gate of a field-effect transistor (BioFET), volatile trace compounds are directly detectable in the ppb range. A complex biochemical detection system in the antenna of the beetle serves as a filter for compounds that provide vital information about its environment. Another advantage of biologically inspired sensory solutions is the evolutionary tuning of the natural detection units towards compounds that are significantly correlated to ecological conditions. Nature has undergone millions of years of survival of the fittest to select compounds that serve organisms reliably as information to trace hosts, mating partners, enemies, or competitors. Because of the diversity of ecological interactions between animals all over the world the biosensor concept and biomimetic approaches can lead to numerous applications for tracking, surveillance and monitoring of environmental and industrial processes.

Electroantennographic responses of red flour beetle Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) to volatile organic compounds

The red flour beetle Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) is the most encountered and destructive stored product insect pest of cereal grains and seeds. Although this beetle has been used as a model organism for many decades, there is no systematic knowledge about antennal detection of host and non‐host volatiles. Electroantennogram responses to 94 selected volatile organic compounds including alkanes, alkenes, alcohols, aldehydes, ketones, carboxylic acids, esters, terpenoids and aromatic compounds were recorded from both sexes of T. castaneum. Overall, female and male T. castaneum exhibited similar electroantennography (EAG) responses. Compounds eliciting the strongest EAG responses within compound groups of chemical similarity were undecane, 1‐hexen‐3‐ol, octanal, 2‐heptanone, hexanoic acid and ethyl hexanoate. Comparison of vapour pressure and EAG amplitudes within homologous series of compounds revealed responses to undecane, octadecane, octanal, nonanal, 2‐heptanone, hexanoic acid and octanoic acid as outstanding. Given that systematic EAG screenings have not been conducted before, these are the best candidates for evaluation in future behavioural studies to unravel their potential for application in integrated pest management strategies of T. castaneum.

Insect Olfaction as a Natural Blueprint of Gas Sensors

Biologically inspired sensory solutions utilize highly developed organs of perception that are evolutionary tuned towards compounds correlated to ecological functions. After millions of years of “survival of the fittest” insects, e.g., are trained to detect specific compounds that serve reliably as cues to find hosts and mating partners, or to avoid enemies and competitors. The multitude of insect species (>1,000,000) and their ecological interactions provide a vast range of possible biosensors based on natural sensory systems. Also biomimetic approaches can lead to various applications for tracking and monitoring of chemical compounds in environmental and industrial processes. Biosensors utilize organic components (e.g., proteins, cells, tissues, or organisms) within a technical appliance. The combination of technical devices with biological sensory units provides detectors which are superior to mere technical solutions in selectivity and sensitivity. For instance, by integrating insect antennae in the gate of a field-effect transistor (BioFET), volatile trace compounds are directly detectable in the ppb range. The complex biochemical detection system in the antenna of the insect serves as a selective detector for compounds that provide vital information about its environment. Thus, knowing the selectivity and sensitivity pattern enables us to design biomimetic semiconductor sensors utilizing the evolutionary experience of insects in combination with reliability and ruggedness of technical semiconductor gas sensors for highly specific gas-sensing tasks.

Sequence matters – selective adaptation in electroantennographic response to binary odour mixtures by the Colorado potato beetle

Chemically mediated behaviour of insects is often strongly affected by mixtures of odour stimuli and their temporal characteristics. Both sensory transduction and central processing of odour mixtures can give rise to several different kinds of interaction, which can influence how individual components are perceived and processed. In particular, odour mixtures have been examined in model experiments as premixed binary mixtures in comparison with pure odour stimuli. Only in few experiments, the influence of the temporal structure of odour mixtures on odour perception has been taken into account. Natural odour stimuli often have a pulsed structure and may in general be superimposed on a background of irrelevant or interfering compounds, which can fluctuate with different frequencies, depending on their source. To achieve a better representation of these natural conditions, our odour mixing experiments apply a new kind of stimulation protocol: odours were not premixed but superimposed with a specific time pattern; one odour stimulus was presented as a longer persisting background and the second stimulus was a superimposed short test signal. To gain an overview of odour interaction patterns in the Colorado potato beetle by causing adaptation of one receptor population at naturally occurring levels of concentration and time intervals, electroantennographic recordings were made on excised antennae. A matrix of 12 stimulus compounds led to 132 pairs of compounds tested, each in the role of background and test stimulus. In 64 cases, the interaction was significantly different, when the role of background and stimulus was exchanged. Interaction patterns ranging from no interference (independence) to suppression were found and assigned to four clearly distinguishable types. We discuss that the observed effects of the presentation sequence in odour mixtures may contribute to the mechanisms of olfactory pattern recognition and olfactory contrast perception by insects.

GÖTTINGEN: Collections in the Departments of “Wildlife Sciences” and “Forest Zoology and Forest Conservation”

Both departments are parts of the Faculty of Forest Sciences and Forest Ecology within the Georg-August-University of Gottingen. Their fields of interest partly overlap which is reflected also in the composition of their scientific collections. The Department of Forest Zoology and Forest Conservation holds a comprehensive collection of the birds of Lower Saxony with about 500 specimens and the historical collection of W.G. Glimmann that comprises birds of prey, owls and wildfowl. Also the insect collection has a considerable historic value: some of the 35,000 specimens were collected by the famous entomologists J.T.C. Ratzeburg and A. Forster. According to the original focus of the Department of Wildlife Sciences, its collection comprises a huge selection of trophies, especially antlers or horns of typical game species. Of historic value are the obsolete game tag register of Germany and some relicts of the royal Hanoverian hunting court, which was dissolved in 1868. Currently, the collection is being rearranged to highlight the important roles that wild animals play in maintaining the functionality and resilience of ecosystems.