Lifestyle and host defense mechanisms of the dung beetle, Euoniticellus intermedius: the toll signaling pathway

More than 5 Years! An Unusually Long-Lived Dung Beetle (Scarabaeinae) in an Andean Agricultural Landscape

Despite their importance as ecological indicators of anthropic perturbation, most of our knowledge about Neotropical dung beetles (Coleoptera: Scarabaeinae) is derived from studies conducted at the community level. To date, at a global scale, there is still incipient knowledge about the population ecology of the Scarabeinae species. The study of these insects at the population level offers new data pertaining to demographic aspects such as population size and adult longevity in the field. On the 6th of August 2017, within a patch of a cloud forest in the municipality of La Celia in Risaralda, Colombia, we recaptured a male specimen of Dichotomius aff. alyattes Harold that was marked 5 years ago, on the 15th of May 2012. The individual was marked with a number 8 on its right elytron and it was recaptured in the same patch forest, which has been sampled since 2008. After an exhaustive review of the field information and literature, this data represents the longest recorded longevity known for Scarabaeinae. Beyond being a fortuitous event, this recapture prompts a review of our ideas regarding the reproductive biology and vulnerability of dung beetle species in landscapes of high anthropic demand, with an emphasis on Neotropical species.

Identification and characterization of novel cecropins from the Oxysternon conspicillatum neotropic dung beetle

Dung beetles are exposed to a complex microbiological ecosystem during their life cycle. Characterization of novel host-defense peptides (HDP) is essential to understanding the host innate immune response in insects. It constitutes a promising alternative to look for new therapeutic agents against pathogenic microbes. We identified four new HDP, Oxysterlins 1, 2, 3, and 4 from the transcriptome of the Oxysternon conspicillatum dung beetle. These HDP display a highly conserved signal peptide and a mature peptide, characterized by an overall positive charge (cationic) (pI: 10.23–11.49), a hydrophobic ratio (ΦH: 35–41), and amphipathicity. Oxysterlins 1, 2, and 3 have a linear α-helix structure, whilst Oxysterlin 4 has a mixture of both α-helix and β-sheet structures without disulfide bonds through bioinformatics prediction and circular dichroism. Oxysterlins are part of the cecropin family group in an exclusive clade related to beetle cecropins. They have predominant antimicrobial activity against Gram-negative bacteria, including multidrug resistant strains (3.12–50 μg/mL) measured by plate microdilution. Their kinetics, in a time-killing curve showed concentration-dependent bactericidal activity. Furthermore, these HDP have low toxicity against human erythrocytes (62.5–500 μg/mL) and Vero cells (250–500 μg/mL). This article describes new HDP of the cecropin family from the Oxysternon conspicillatum dung beetle, with antimicrobial activity against multidrug resistant bacteria and low toxicity.

Novel members of the adipokinetic hormone family in beetles of the superfamily Scarabaeoidea

Eight beetle species of the superfamily Scarabaeoidea were investigated with respect to peptides belonging to the adipokinetic hormone (AKH) family in their neurohemal organs, the corpora cardiaca (CC). The following beetle families are represented: Scarabaeidae, Lucanidae, and Geotrupidae. AKH peptides were identified through a heterospecific trehalose-mobilizing bioassay and by sequence analyses, using liquid chromatography coupled to positive electrospray mass spectrometry (LC-ESI-MS) and analysis of the tandem MS² spectra obtained by collision-induced dissociation. All the beetle species have octapeptide AKHs; some have two AKHs, while others have only one. Novel AKH members were found in Euoniticellus intermedius and Circellium bacchus (family Scarabaeidae), as well as in Dorcus parallelipipedus (family Lucanidae). Two species of the family Geotrupidae and two species of the Scarabaeidae subfamily Cetoniinae contain one known AKH peptide, Melme-CC, while E. intermedius produces a novel peptide code named Euoin-AKH: pEINFTTGWamide. Two AKH peptides were each identified in CC of C. bacchus and D. parallelipipedus: the novel Cirba-AKH: pEFNFSAGWamide and the known peptide, Scade-CC-I in the former, and the novel Dorpa-AKH: pEVNYSPVW amide and the known peptide, Melme-CC in the latter. Kheper bonelli (subfamily Scarabaeinae) also has two AKHs, the known Scade-CC-I and Scade-CC-II. All the novel peptides were synthesized and the amino acid sequence assignments were unequivocally confirmed by co-elution of the synthetic peptides with their natural equivalent, and identical MS parameters of the two forms. The novel synthetic peptides are all active in inducing hypertrehalosemia in cockroaches.