Carabidae Semiochemistry: Current and Future Directions

Sexual dimorphism of Dyschiriini (Coleoptera, Carabidae): Comparative morphological SEM study of palpi sensilla and its possible role in intraspecific chemical communication

Sexual dimorphism in Dyschiriini (Coleoptera, Carabidae) consists of the presence of an autapomorphic sensory area in apical palpomeres of males, here named as Male Palpi Sensory Area (MPSA). In this work, microstructure of palpi, with focus on MPSA, is characterized and formally described using Scanning Electron Microscopy (SEM). Interspecific variability among 13 species and three subgenera of Dyschirius Bonelli, 1810 and one species of Reicheiodes Ganglbauer, 1891 is assessed. Palpi of studied Dyschiriini presented up to 4 sensilla classes (coeloconica, basiconica, digitiformia, trichodea) in both sexes, while males had one more class (sensilla placodea) found grouped in MPSA. Measurements of sensilla and MPSA are provided. Differences among taxa corresponded to development grade of MPSA and its number of sensilla placodea. The MPSA of Dyschirius (Dyschirius) thoracicus Rossi, 1790 were clearly different to the rest of the studied subgenera and species of Dyschirius and Reicheiodes, whose MPSA were similar and had slight intraspecific variability. We suggest that function of MPSA is likely detection of female pheromones, which would evidence chemical communication between sexes. We hypothesize that evolution of MPSA could be related to burrowing habits of Dyschiriini and its possible sexual behavior in soil tunnels. Study of MPSA may help to elucidate phylogenetic relationships among members of the tribe.

Repellent and Attractant Activities of Organic Compounds on Female and Male Philonthus decorus (Coleoptera, Staphylinidae)

The use of organic compounds in different spheres of human activity is accompanied by their influx to and accumulation in the environment. The negative impact of those compounds can be one of the reasons for a decline in populations and biodiversity of aboveground invertebrates. Chemical compounds can potentially cause a variety of effects (attractant or repellent) on insects, including species of the Staphylinidae family. In a laboratory experiment, we identified repellent and attractant influence of 40 organic compounds and mixtures of compounds (acids, alcohols, ketones, phenols, aldehydes, aromatic carbohydrates solvents, and vehicle fuels) on Philonthus decorus Gravenhorst, 1802. The ambulatory responses of the males and females to the same chemical compounds most often varied. A strong repellent activity against both sexes of Ph. decorus was caused by oleic acid, while hexane repelled the males. Acetic acid, 1-butanol, and ammonia solution were found to be strongly repellent against females. A moderate (average) repellent activity towards male Ph. decorus was displayed by organic solvents and fuels, some alcohols (isopropanol, isoamyl alcohol, methanol, ethanol), acids (acetic, formic acid), aromatic carbohydrates (toluene, xylene), and formaldehyde. Female Ph. decorus in general were less sensitive to the odors. The list of repellents with moderate activity against the females was much shorter: solvent 646, white spirit, toluene, isopropanol, isoamyl alcohol, citric and oxalic acids, and glycerol. Moderate attractant activity for Ph. decorus was exhibited by some amino acids, alcohols, and fuel mixes: glycine and L-cysteine (for the males), and phenylalanine, methanol, and diesel fuel (for the females). The rest of the 40 chemical compounds we studied caused no ambulatory responses in Ph. decorus. The difficulties we encountered in the interpretation of the results suggest a need for further experimental studies that would expand the knowledge of the chemoecology of insects.

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.

The chemical composition of the secretions, their antibacterial activity, and the pygidial gland morphology of selected European Carabini ground beetles (Coleoptera: Carabidae)

The pygidial glands of carabids produce strong-smelling vapours. In this study, we examined the chemical composition of the gland secretions and the structure of the glands in five species of Carabini ground beetles (one species from the subtribe Calosomatina and four species from the subtribe Carabina): Calosoma (Calosoma) maderae (Fabricius, 1775), Carabus (Carabus) granulatus Linnaeus, 1758, C. (Limnocarabus) clathratus Linnaeus, 1760, C. (Carabus) ulrichii Germar, 1823, and C. (Procerus) gigas Creutzer, 1799. Additionally, we tested the antibacterial potential of the pygidial gland secretions of the two latter species against 11 bacterial strains. In order to detect the chemical content of the secretions, we used gas chromatography–mass spectrometry (GC–MS). The secretion extracts were applied against selected strains of medically important bacteria. We used bright-field microscopy to examine the morphology of the glands. We discovered a total of 11 chemical compounds in the pygidial gland extracts of the ground beetles we analysed. Ten of these compounds were identified as seven carboxylic acids, two hydrocarbons, and one aromatic aldehyde, while one chemical remained unidentified. Most of the components were isolated from the secretion of C. (L.) clathratus (nine), while the lowest number of compounds was found in C. (P.) gigas (two). Methacrylic acid was the most dominant compound by percentage in all five species, while angelic acid was also detected in all samples. As expected, salicylaldehyde was exclusively found in the species of the genus Calosoma Weber, 1801. The secretion of C. (P.) gigas was shown to achieve the highest level of antibacterial activity against Pseudomonas aeruginosa, Salmonella enterica, and S. typhimurium (even the same level as the positive control streptomycin), while the secretion of C. (C.) ulrichii achieved the highest antimicrobial potential against Staphylococcus epidermidis, S. aureus, Listeria monocytogenes, and Bacillus cereus. The most noticeable difference in the structure of the glands between the two genera is that the reservoir in Calosoma is more significantly narrowed as it leads into the efferent duct, compared to that of Carabus.

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.

Microbial Volatile Organic Compounds from Tempered and Incubated Grain Mediate Attraction by a Primary but Not Secondary Stored Product Insect Pest in Wheat

There has been a dearth of research elucidating the behavioral effect of microbially-produced volatile organic compounds on insects in postharvest agriculture. Demonstrating attraction to MVOC’s by stored product insects would provide an additional source of unique behaviorally-relevant stimuli to protect postharvest commodities at food facilities. Here, we assessed the behavioral response of a primary (Rhyzopertha dominica) and secondary (Tribolium castaneum) grain pest to bouquets of volatiles produced by whole wheat that were untempered, or tempered to 12%, 15%, or 19% grain moisture and incubated for 9, 18, or 27 days. We hypothesized that MVOC’s may be more important for the secondary feeder because they signal that otherwise unusable, intact grains have become susceptible by weakening of the bran. However, contrary to our expectations, we found that the primary feeder, R. dominica, but not T. castaneum was attracted to MVOC’s in a wind tunnel experiment, and in a release-recapture assay using commercial traps baited with grain treatments. Increasing grain moisture resulted in elevated grain damage detected by near-infrared spectroscopy and resulted in small but significant differences in the blend of volatiles emitted by treatments detected by gas chromatography coupled with mass spectrometry (GC–MS). In sequencing the microbial community on the grain, we found a diversity of fungi, suggesting that an assemblage was responsible for emissions. We conclude that R. dominica is attracted to a broader suite of MVOC’s than T. castaneum, and that our work highlights the importance of understanding insect-microbe interactions in the postharvest agricultural supply chain.

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.

Cell type innovation at the tips of the animal tree

Understanding how organs originate is challenging due to the twin problems of explaining how new cell types evolve and how collective interactions between cell types arise and become selectively advantageous. Animals are assemblages of organs and cell types of different antiquities, and among the most rapidly and convergently evolving are exocrine glands and their constituent secretory cell types. Such structures have arisen independently thousands of times across the Metazoa, impacting how animals chemically interact with their environments. The recurrent evolution of exocrine systems provides a paradigm for examining how qualitative phenotypic novelties arise from variation at the cellular level. Here, we take a hierarchical perspective, focusing on the evolutionary assembly of novel biosynthetic pathways and secretory cell types, and how both selection and non-adaptive molecular processes may combine to build the complex, modular architectures of many animal glands.

Isolation and identification of attractants from the pupae of three lepidopteran species for the parasitoid Chouioia cunea Yang

BACKGROUND

Chouioia cunea Yang (Hymenoptera: Eulophidae) is a parasitic wasp and natural enemy of several lepidopteran pests during their pupal stage. The volatiles from pupae of three hosts, Hyphantria cunea (Arctiidae), Antheraea pernyi (Saturniidae) and Lymantria dispar (Erebidae), were analyzed and compared to elucidate the chemical cues used by C. cunea to locate its hosts.

RESULTS

The attraction of C. cunea to H. cunea pupae has no obvious association with the types of plant leaves consumed by H. cunea before pupation. C. cunea exhibited the strongest attraction to the pupae of H. cunea, followed by those of A. pernyi and L. dispar based on behavioral experiments. Gas chromatography-mass spectrometry and GC-electroantennography (GC-EAD) analyses showed that these three host pupae consisted of essentially the same active volatile components but at different relative amounts. Active components derived from these pupae by GC-EAD were alkanes from C12 to C27, and C. cunea showed different levels of attraction to different single compounds.

CONCLUSION

Host location by C. cunea primarily depends on common compounds emanating from the pupae of several host species. The relative amount of each component varies across host species, guiding host preferences by C. cunea. Optimal blends of several components were identified. Understanding the chemical cues used by C. cunea to locate its host could increase the possibility of developing attractants for parasitic wasps and subsequently increasing the parasitism rate of C. cunea on various hosts. © 2019 Society of Chemical Industry.

Molecular evolution of gland cell types and chemical interactions in animals

Across the Metazoa, the emergence of new ecological interactions has been enabled by the repeated evolution of exocrine glands. Specialized glands have arisen recurrently and with great frequency, even in single genera or species, transforming how animals interact with their environment through trophic resource exploitation, pheromonal communication, chemical defense and parental care. The widespread convergent evolution of animal glands implies that exocrine secretory cells are a hotspot of metazoan cell type innovation. Each evolutionary origin of a novel gland involves a process of 'gland cell type assembly': the stitching together of unique biosynthesis pathways; coordinated changes in secretory systems to enable efficient chemical release; and transcriptional deployment of these machineries into cells constituting the gland. This molecular evolutionary process influences what types of compound a given species is capable of secreting, and, consequently, the kinds of ecological interactions that species can display. Here, we discuss what is known about the evolutionary assembly of gland cell types and propose a framework for how it may happen. We posit the existence of 'terminal selector' transcription factors that program gland function via regulatory recruitment of biosynthetic enzymes and secretory proteins. We suggest ancestral enzymes are initially co-opted into the novel gland, fostering pleiotropic conflict that drives enzyme duplication. This process has yielded the observed pattern of modular, gland-specific biosynthesis pathways optimized for manufacturing specific secretions. We anticipate that single-cell technologies and gene editing methods applicable in diverse species will transform the study of animal chemical interactions, revealing how gland cell types are assembled and functionally configured at a molecular level.

Tools in the Investigation of Volatile Semiochemicals on Insects: From Sampling to Statistical Analysis

The recognition of volatile organic compounds (VOCs) involved in insect interactions with plants or other organisms is essential for constructing a holistic comprehension of their role in ecology, from which the implementation of new strategies for pest and disease vector control as well as the systematic exploitation of pollinators and natural enemies can be developed. In the present paper, some of the general methods employed in this field are examined, focusing on their available technologies. An important part of the investigations conducted in this context begin with VOC collection directly from host organisms, using classical extraction methods, by the employment of adsorption materials used in solid-phase micro extraction (SPME) and direct-contact sorptive extraction (DCSE) and, subsequently, analysis through instrumental analysis techniques such as gas chromatography (GC), nuclear magnetic resonance (NMR) and mass spectrometry (MS), which provide crucial information for determining the chemical identity of volatile metabolites. Behavioral experiments, electroantennography (EAG), and biosensors are then carried out to define the semiochemicals with the best potential for performing relevant functions in ecological relationships. Chemical synthesis of biologically-active VOCs is alternatively performed to scale up the amount to be used in different purposes such as laboratory or field evaluations. Finally, the application of statistical analysis provides tools for drawing conclusions about the type of correlations existing between the diverse experimental variables and data matrices, thus generating models that simplify the interpretation of the biological roles of VOCs.