Cerrado ash reduces volatile emissions from faeces but does not influence the olfactory responses of the dung beetles

Fire is a key natural disturbance influencing physical, chemical, and biological processes in the Cerrado. Ash, a fire byproduct, may significantly influence soil macrofauna through its chemical properties. Dung beetles (Scarabaeinae), critical components of Cerrado soil macrofauna, provide key ecological functions and services. Here, we investigate whether ash deposition from burned Cerrado grassland vegetation alters odour-guided foraging in Dichotomius bos, a native dung beetle species, by modifying the composition of volatile organic compounds (VOCs) in faecal resources. We hypothesised that ash would reduce VOC emissions from faeces, thereby decreasing their attractiveness to D. bos. Volatiles from swine faeces, with and without ash, were collected via solid-phase microextraction (SPME) and analysed using gas chromatography-mass spectrometry (GC-MS). Eight VOCs were selected based on their relative abundance and identification: dimethyl trisulfide (DMTS), p-cresol, 3-ethylphenol, 2-undecanone, 2-methylindole, skatole, (Z)-6-pentadecen-1-ol, and heptadecan-1-ol. The relative abundance of all target compounds was reduced in ash-exposed faeces. In four-choice olfactometer trials, D. bos exhibited a strong attraction to swine faecal odours. However, despite reduced VOC relative abundance in ash-treated faeces, beetles showed equivalent attraction to odours from faeces with and without ash. These results suggest D. bos is resilient to post-fire chemical changes in resource odours, likely reflecting adaptations to fire-prone Cerrado ecosystems. Investigating dung beetle responses to fire-derived alterations in resource chemistry may inform management strategies to conserve Cerrado biodiversity under fire regimes.