Molecular Diversity of Compounds from Pygidial Gland Secretions of Cave-Dwelling Ground Beetles: The First Evidence

Morphology of the pygidial glands and chemical composition of their secretions in two species of tiger beetles (Carabidae: Cicindelinae)

Pygidial glands are a common feature of all adephagans and their products play an important role in defense against predators. The morphology of the pygidial glands and the chemistry of their secretion were studied for the first time in two species of tiger beetles - Cicindela (Cicindela) sylvicola Dejean, 1822 and Cylindera (Cylindera) germanica (Linnaeus, 1758). The glands were examined by both bright-field microscopy and nonlinear microscopy. All morphological structures of the glands were measured and described in detail. The structures mentioned were compared with those of related taxa. The secretion extracts from the pygidial glands of the investigated taxa contained a total of 24 compounds, which were detected by gas chromatography-mass spectrometry (GC-MS). The secretion mixture of C. (C.) germanica was more complex (21 chemicals) than that of C. (C.) sylvicola (11 ones). Benzaldehyde was present in both secretion samples. Hydrocarbons were the most abundant group of secretory compounds. The purpose of the compounds, their distribution within the subfamily Cicindelinae and their effects on the ecology of the group were discussed.

On the Diversity of Semiochemicals of the Pygidial Gland Secretions of Subterranean Ground Beetles (Coleoptera: Carabidae)

Pygidial glands are of great importance to ground beetles for defense against predators, especially for the species that live in subterranean habitats. The purpose of our study is to better understand the chemistry of the pygidial gland secretions of subterranean ground beetles, as well as the function and structure of the glands. We studied both the chemical composition of the pygidial gland secretion and morphology of the glands in adults of the troglophilic ground beetle species Laemostenus (Antisphodrus) cavicola (Schaum, 1858). The chemical composition of its defensive secretion was revealed using gas chromatography-mass spectrometry (GC-MS), while pygidial gland morphology of the beetle was investigated using bright-field microcopy. In total, seven chemical compounds were detected in the secretion mixture. Formic acid was the most dominant compound, followed by dodecyl acetate and undecane. Other chemicals were present in minor amounts. The morphological structure of the pygidial glands of L. (A.) cavicola was compared with the structure of the glands of the related congeneric troglophilic species Laemostenus (Pristonychus) punctatus (Dejean, 1828). Summary data on the semiochemicals that have been recorded so far in subterranean ground beetle species are presented, and the differences in the chemical composition of the secretions between and among troglobitic and troglophilic species are discussed. So far, forty-four compounds have been detected in four subterranean ground beetle species (two troglobites belonging to the tribe Trechini and two troglophiles belonging to the tribe Sphodrini). The results of this study indicate the great diversity of chemicals in the pygidial gland secretions of subterranean ground beetles.

Volatiles released by Beauveria bassiana induce oviposition behavior in the fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae)

Microbial volatile organic compounds may act as semiochemicals, inciting different behavioral responses in insects. Beauveria bassiana is an entomopathogenic fungus, and physiological and environmental factors are positively related to fungal virulence. In this study, we examined the volatile profiles produced by eight B. bassiana strains, isolated from soil plots and mycosed insect cadavers, with different speeds of kill and determined if these compounds induce oviposition behavior in Spodoptera frugiperda. Fungal volatilome analysis revealed differences between the isolates. Isolates from mycosed insects showed higher virulence, larger egg mass area and length, and a higher number of eggs by mass, than those obtained from soil. Furthermore, a dilution of the fungal odoriferous compounds increased the insect response, suggesting that S. frugiperda is highly susceptible to the fungal compound's fingerprint. Otherwise, the insect response to the natural blend of volatiles released by the fungus was different from that obtained with 3-methylbutanol, which was the most abundant compound in all isolates. The ability of an entomopathogen to produce volatiles that can induce olfactory stimulation of egg-laying behavior could represent an ecological adaptive advantage in which the entomopathogen stimulates the insect population growth.

Pygidial glands of three ground beetle taxa (Insecta, Coleoptera, Carabidae): a study on their morphology and chemical composition of their secretions

Morphology of the pygidial glands and chemical compositions of their secretion were analysed in the adults of three selected ground beetle taxa. Secretions of pygidial glands of Cychrus (Cychrus) semigranosus, Patrobus atrorufus and Pterostichus (Platysma) niger were chemically tested. Additionally, pygidial glands of the latter two species were investigated using bright-field microscopy and nonlinear microscopy and morphological features of the glands were described in detail. Both C. (C.) semigranosus and P. atrorufus were studied for the first time in terms of chemical ecology, while the latter species was analysed for the first time in terms of pygidial gland morphology. Altogether, eight compounds were detected in the dichloromethane extracts of the pygidial gland secretions of the three ground beetle taxa analysed. The simplest secretion mixtures were present in C. (C.) semigranosus and P. atrorufus (with two compounds each), while the extract of P. (P.) niger contained five compounds. The presence of 1-tetradecanol in the secretion of P. (P.) niger represents the first finding of this compound from the pygidial gland secretion extracts of ground beetles.

Pygidial Glands in Carabidae, an Overview of Morphology and Chemical Secretion

Predator community structure is an important selective element shaping the evolution of prey defence traits and strategies. Carabid beetles are one of the most diverse families of Coleoptera, and their success in terrestrial ecosystems is related to considerable morphological, physiological, and behavioural adaptations that provide protection against predators. Their most common form of defence is the chemical secretion from paired abdominal pygidial glands that produce a heterogeneous set of carboxylic acids, quinones, hydrocarbons, phenols, aldehydes, and esters. This review attempts to update and summarise what is known about the pygidial glands, with particular reference to the morphology of the glands and the biological function of the secretions.

Chemistry and morphology of the pygidial glands in four Pterostichini ground beetle taxa (Coleoptera: Carabidae: Pterostichinae)

Morphology of the pygidial glands and chemical composition of their secretions in adults of four ground beetle representatives of the Pterostichini tribe (Coleoptera: Carabidae) were analysed. Molops (Stenochoromus) montenegrinus, Pterostichus (Cophosus) cylindricus, P. (Feronidius) melas and P. (Pseudomaseus) nigrita were chemically tested, while the latter three species were morphologically investigated. Pterostichus (C.) cylindricus, P. (P.) nigrita and M. (S.) montenegrinus were chemically studied for the first time. Altogether, 23 chemical compounds were isolated using gas chromatography-mass spectrometry (GC-MS), of which some are new for Pterostichini or even Carabidae. Methacrylic acid was present in all species analysed. It was predominant in the secretion extract of P. (C.) cylindricus and P. (F.) melas. Isobutyric and 2-methylbutyric acids were the major components in the secretion of M. (S.) montenegrinus. Undecane, methacrylic and tiglic acids were the main components in the secretion of P. (P.) nigrita. The simplest chemical mixture was found in P. (C.) cylindricus (two compounds), while the most complex one was detected in P. (P.) nigrita (15 compounds). No significant differences in the chemical composition of the pygidial gland secretions were evidenced in P. (C.) cylindricus sampled from the same area and in the same season in two different years. Morphology of the pygidial glands of the studied species was analysed for the first time. Morphological features of the pygidial glands were observed using bright-field microscopy and nonlinear microscopy and described in details.

Bat guano-dwelling microbes and antimicrobial properties of the pygidial gland secretion of a troglophilic ground beetle against them

Bat guano is an important source of microbial diversity in caves and can be a source of potential pathogens. Laemostenus (Pristonychus) punctatus is a guanophilic ground beetle species, which pygidial gland secretion exhibits action against pathogenic and other microbes. The distribution and diversity of microbes in bat guano from a karstic cave were determined in this study. Additionally, antimicrobial activity of the pygidial gland secretion of L. (P.) punctatus against guano-dwelling microbes was tested; minimal inhibitory concentration (MIC) and chemical composition of the secretion were analyzed. In total, 63 different bacterial species and 16 fungal morphotypes were isolated from guano samples by the cultivation method and confirmed using and phenotypic characterization and molecular identification. There was a difference in the composition of certain microorganisms between the sampling points (cave locations) and between the guano layers. The largest number of bacterial isolates belongs to the genera Lysinibacillus and Paenibacillus, while Pseudomonas species were highly abundant at the innermost sampling point. For the guanophilic fungi, the majority are ascomycetes, with Penicillium and Aspergillus as the most dominant genera. Meyerozyma guilliermondii was the only yeast species found in the guano samples. The most sensitive isolates were Enterococcus eurekensis (MIC 0.007 mg/mL) and Escherichia fergusonii (MIC 0.028 mg/mL). The most sensitive fungal isolates were M. guilliermondii, Penicillium expansum, and Trichoderma harzianum (MIC 0.15 mg/mL). This study opens a new possibility for better understanding of ecological relations between microorganisms and troglophilic ground beetles and for detailed investigations of morpho-anatomical aspects of pygidial glands.

Antifungal activity of the pygidial gland secretion of Laemostenus punctatus (Coleoptera: Carabidae) against cave-dwelling micromycetes

The antifungal potential of the pygidial gland secretion of the troglophilic ground beetle Laemostenus punctatus from a cave in Southeastern Serbia against cave-dwelling micromycetes, isolated from the same habitat, has been investigated. Eleven collected samples were analyzed and 32 isolates of cave-dwelling fungi were documented. A total of 14 fungal species were identified as members of the genera Aspergillus, Penicillium, Alternaria, Cladosporium, Rhizopus, Trichoderma, Arthrinium, Aureobasidium, Epicoccum, Talaromyces, and Fusarium. Five isolates were selected for testing the antifungal activity of the pygidial gland secretion: Talaromyces duclauxi, Aspergillus brunneouniseriatus, Penicillium sp., Rhizopus stolonifer, and Trichoderma viride. The microdilution method has been applied to detect minimal inhibitory concentrations (MICs) and minimal fungicidal concentrations (MFCs). The most sensitive isolate was Penicillium sp., while the other isolates demonstrated a high level of resistance to the tested agent. L. punctatus has developed a special mechanism of producing specific compounds that act synergistically within the secretion mixture, which are responsible for the antifungal action against pathogens from the cave. The results open opportunities for further research in the field of ground beetle defense against pathogens, which could have an important application in human medicine, in addition to the environmental impact, primarily.

Chemical Ecology of Cave-Dwelling Millipedes: Defensive Secretions of the Typhloiulini (Diplopoda, Julida, Julidae)

Cave animals live under highly constant ecological conditions and in permanent darkness, and many evolutionary adaptations of cave-dwellers have been triggered by their specific environment. A similar "cave effect" leading to pronounced chemical interactions under such conditions may be assumed, but the chemoecology of troglobionts is mostly unknown. We investigated the defensive chemistry of a largely cave-dwelling julid group, the controversial tribe "Typhloiulini", and we included some cave-dwelling and some endogean representatives. While chemical defense in juliform diplopods is known to be highly uniform, and mainly based on methyl- and methoxy-substituted benzoquinones, the defensive secretions of typhloiulines contained ethyl-benzoquinones and related compounds. Interestingly, ethyl-benzoquinones were found in some, but not all cave-dwelling typhloiulines, and some non-cave dwellers also contained these compounds. On the other hand, ethyl-benzoquinones were not detected in troglobiont nor in endogean typhloiuline outgroups. In order to explain the taxonomic pattern of ethyl-benzoquinone occurrence, and to unravel whether a cave-effect triggered ethyl-benzoquinone evolution, we classed the "Typhloiulini" investigated here within a phylogenetic framework of julid taxa, and traced the evolutionary history of ethyl-benzoquinones in typhloiulines in relation to cave-dwelling. The results indicated a cave-independent evolution of ethyl-substituted benzoquinones, indicating the absence of a "cave effect" on the secretions of troglobiont Typhloiulini. Ethyl-benzoquinones probably evolved early in an epi- or endogean ancestor of a clade including several, but not all Typhloiulus (basically comprising a taxonomic entity known as "Typhloiulus sensu stricto") and Serboiulus. Ethyl-benzoquinones are proposed as novel and valuable chemical characters for julid systematics.

The pygidial gland secretion of the forest caterpillar hunter, Calosoma (Calosoma) sycophanta: the antimicrobial properties against human pathogens

Recently, various insect secretions have been tested as possible antimicrobial agents. In beetles, these secretions are essentially products of various exocrine glands, of which particular emphasis is on pygidial glands that are common for the suborder Adephaga. The antimicrobial potential of the pygidial gland secretion isolated from the adults of Calosoma sycophanta against human pathogens has been tested and compared with the potential of other carabid species, particularly within the tribe Carabini. The antimicrobial assay includes a microdilution method which was applied in order to determine the minimal inhibitory, minimal fungicidal and minimal bactericidal concentrations. It has been tested the effect of the secretion against eight strains of fungal and eight strains of bacterial species. The secretion sample of the tested carabid species has shown statistically significant antifungal effect against all strains of treated micromycetes, the highest in comparison with previously tested carabids (Carabus spp., Laemostenus punctatus and Abax parallelepipedus). Aspergillus versicolor proved to be the most sensitive micromycete, while the remaining seven fungal strains have shown the same level of sensibility. In comparison with commercial mycotics ketoconazole and bifonazole, applied as positive controls, the tested secretion showed much higher antifungal activity for all fungal strains. Antibacterial effect has been manifested only against one bacterial strain (Escherichia coli), contrary to other previously studied carabid species. These observations might have a significant impact on the ecological domain and possible purpose in biomedical studies and applications in the future. Additionally, morpho-histology of the pygidial glands of C. sycophanta is investigated and discussed.

Antimicrobial activity of the pygidial gland secretion of the troglophilic ground beetle Laemostenus (Pristonychus) punctatus (Dejean, 1828) (Insecta: Coleoptera: Carabidae)

The antimicrobial activity of the pygidial gland secretion released by adult individuals of the troglophilic ground beetle Laemostenus (Pristonychus) punctatus (Dejean, 1828), applying microdilution method with the aim to detect minimal inhibitory concentration, minimal bactericidal concentration and minimal fungicidal concentration, has been investigated. In addition, morphology of the pygidial glands is observed. We have tested 16 laboratory and clinical strains of human pathogens - eight bacterial both gram-positive and gram-negative species and eight fungal species. The pygidial secretion samples have showed antimicrobial properties against all strains of treated bacteria and fungi. Micrococcus flavus proved to be more resistant compared with other bacterial strains. More significant antimicrobial properties of the secretion are observed against Escherichia coli, which proved to be the most sensitive bacteria. Aspergillus fumigatus proved to be the most resistant, while Penicillium ochrochloron and Penicillium verrucosum var. cyclopium the most sensitive micromycetes. Commercial antibiotics Streptomycin and Ampicillin and antimycotics Ketoconazole and Bifonazole, applied as positive controls, showed higher antibacterial properties for all bacterial and fungal strains, except for P. ochrochloron, which proved to be more resistant on Ketoconazole compared with the pygidial gland secretion of L. (P.) punctatus. Apart from the role in ecological aspects, the antimicrobial properties of the tested secretion possibly might have medical significance in the future.