Viktoria Zagler

PDF der Diplomarbeit im Hochschulschriften-Service der Universität Wien

Dung scent profiles or single scent compounds: What do dung beetles use to detect their food?

In coprophagous beetles the successful detection of suitable food sources as well as the selection of preferred dung types most likely are facilitated by volatile odorants emitted by the dung. However, it is largely unknown whether entire dung scent profiles or individual dung scent compounds are used by dung beetles to detect their food source. This study quantified species richness and composition of dung beetle assemblages as well as food preferences of individual species attracted to different dung types. Field work was conducted in a farmland area in Lower Austria between 3 August and 3 September 2007. The odors of used dung types were analyzed to evaluate the importance of emitted volatile odorants for species composition and the occurrence of individual species. A total of 1,057 dung beetle individuals belonging to 15 species were caught by pitfall traps, each baited with dung from one of seven different dung producers represented by herbivores (sheep, horse, cattle, and goose), omnivores (human, and pig) and one carnivore (dog). One additional control trap remained unbaited. The dung scent composition emitted by different dung types was analyzed using gas chromatography-mass spectrometry. A total of 17 dung scent odorants out of 6 compound classes (fatty acid derivates, benzenoids, sulphur-containing compounds, nitrogen-containing compounds, ketones, sesquiterpenoids) were detected in the scent samples. Composition of dung beetle communities as well as dung scent profiles differed significantly between dung types. Seven dung odorants (4-Propylphenol, 3-Methylindole, unknown fatty acid derivate, β-Caryophyllene, Indole, unknown nitrogen-containing compound and Dimethyl disulfide) were found to affect the occurrence of the 4 most abundant dung beetle species, all belonging to the genus Onthophagus, in the pitfall trap samples. Some compounds are closely associated with the nutrition of the dung producers and therefore may be used by dung-feeding beetles as indicator for food quality. Not all dung scents related to the occurrence of individual dung beetle species acted as attractant, but appeared to have a strong negative effect on the attractiveness of exposed dung baits. Our study indicates that both single dung scent compounds and a combination of different scents are used by dung beetles to detect suitable dung sources. The importance of determined dung scents possible acting as cues for the selection of adequate food by coprophagous beetles has to be further evaluated by choice experiments.