The evidence of trace amounts of methane of uncertain origin released from cerambycid larvae of Stictoleptura rubra

Insects release methane as a result of their symbiosis with methanogenic microorganisms. This phenomenon has been well studied in termites but is still poorly known in other insects, among which the most likely methane producers are wood-feeders. We applied two methodological approaches to examine whether the wood-feeding larvae of Stictoleptura rubra (Cerambycidae, Coleoptera) release methane. By means of the precise gas chromatography we detected a methane release at the rate of 0.02-0.05 nmol/gxhr. We also investigated the gut Archaea assemblage by 16S rRNA gene sequencing and T-RFLP analysis. Halophilic archaea but no known methanogens were detected. Combined with our chromatographic studies showing small but significant amount of methane release, one possible explanation is that the detected archaeons are methanogenic although this is unlikely. Our results offer the first evidence of methane release by a longhorn (cerambycid) beetle, which may be the small amounts of methane all organisms produce abiotically but the actual mechanism of this consistent methanogenesis remains intriguingly unknown. Originality-Significance StatementThe research presented here goes beyond the long-established tracks on the symbiotic basis of insect methanogenesis and shows that there are areas still scarcely covered so far, with great exploratory potential.