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Faculty for Biology, Chemistry and Earth Sciences

Department of Biology Education - Prof. Dr. Franz X. Bogner

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Bogner, FX; Boppré, M: Single cell recordings reveal hydroxydanaidal as the volatile compound attracting insects to pyrrolizidine alkaloids., Entomologia Experimentalis et Applicata, 50, 171-184 (1989)
Employment of electrophysiology in combination with simple chemical techniques elucidated the volatile which permit the localization of sources of pyrrolizidine alkaloids (Pas) by insects exploiting these secondary plant metabolites. Single cell recordings in Rhodogastria moths (Arctiidae) revealed a physiologically clearly separable type of antennal sensilla basiconica (´SBII´) which responds to headspace air of certain Pas (e.g. monocrotaline), but not to a great variety of ´odorants´. However, stimulus sources of 1 µg were required to elicit responses and the maximum frequency (obtained with stimulus sources of 5 mg) was only 50 imps/s. This suggested the occurrence of small amounts of airborne PA degradation products. Extraction and hydrolysis experiments in combination with thin-layer chromatography and using the sensory responses of antennal receptor cells as biological detectors eventually demonstrated that the dihydropyrrolizine ´hydroxydanaidal´ emanates in small amounts from sources of those Pas which contain retronecine and heliotridine, respectively, as necine moiety. This substance was also implicated as the volatile mediating attraction of the insects to PA-containing plants, as well as to artificial PA-baits. With respect to the high sensitivity and specificity of SB-II-receptor cells to hydroxydanaidal, in particular to its R(-)-enantiomer, they are analogous to the well studied receptor cells for sex-attractant pheromones in Lepidoptera. Similar results were obtained with Danaus (Danainae) ans Euchromia (Ctenuchiidae). Initial behavioural tests have proven the attractive power of hydroxydanaidal for PA-insects and thus corroborate our interpretation of the electrophysiological findings. Keywords: Rhodogastria, Arctiidae, pharmacophagy, attraction, pyrrolizidine alkaloids, hydroxydanaidal, single cell recordings, olfaction
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