Orange/lemon-scented beetles: opposite enantiomers of limonene as major constituents in the defensive secretion of related carabids

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.

Carabidae Semiochemistry: Current and Future Directions

Ground beetles (Carabidae) are recognized for their diverse, chemically-mediated defensive behaviors. Produced using a pair of pygidial glands, over 250 chemical constituents have been characterized across the family thus far, many of which are considered allomones. Over the past century, our knowledge of Carabidae exocrine chemistry has increased substantially, yet the role of these defensive compounds in mediating behavior other than repelling predators is largely unknown. It is also unclear whether non-defensive compounds produced by ground beetles mediate conspecific and heterospecific interactions, such as sex-aggregation pheromones or kairomones, respectively. Here we review the current state of non-exocrine Carabidae semiochemistry and behavioral research, discuss the importance of semiochemical research including but not limited to allomones, and describe next-generation methods for elucidating the underlying genetics and evolution of chemically-mediated behavior.

Effects of d- and l-limonene on the pregnant rat myometrium in vitro

Aim

To study the effects of d- and l-limonene on pregnant rat myometrial contractility in vitro, and investigate how these effects are modified by other agents. D- and l-limonene (10⁻¹³-10⁻⁸ M) caused myometrial contraction in a dose-dependent manner.

Methods

Contractions of uterine rings from 22-day-pregnant rats were measured in an organ bath in the presence of d- or l-limonene (10⁻¹³-10⁻⁸ M) and nifedipine (10⁻⁸ M), tetraethyl-ammonium (10⁻³ M), theophylline (10⁻⁵ M), or paxilline (10⁻⁵ M). Uterine cyclic adenosine monophosphate (cAMP) level was detected by enzyme immunoassay. Oxidative damage was induced by methylglyoxal (3 × 10⁻² M) and the alteration was measured via noradrenaline (1 × 10⁻⁹ to 3 × 10⁻⁵ M) -induced contractions.

Results

Pre-treatment with nifedipine (10⁻⁸ M), tetraethylammonium (10⁻³ M), and theophylline (10⁻⁵ M) attenuated the contracting effect of d- and l-limonene, while in the presence of paxilline (10⁻⁵ M) d- and l-limonene were ineffective. The two enantiomers decreased the myometrial cAMP level, but after paxilline pretreatment the cAMP level was not altered compared with the control value. Additionally, l-limonene (10⁻⁶ M) diminished consequences of oxidative damage caused by methylglyoxal (3 × 10⁻² M) on contractility, whereas d-limonene was ineffective.

Conclusion

Our findings suggest that l-limonene has an antioxidant effect and that both d-and l-limonene cause myometrial contraction through activation of the A_2A receptor and opening of the voltage-gated Ca²⁺ channel. It is possible that limonene-containing products increase the pregnant uterus contractility and their use should be avoided during pregnancy.

Enantiomeric natural products: occurrence and biogenesis

In nature, chiral natural products are usually produced in optically pure form-however, occasionally both enantiomers are formed. These enantiomeric natural products can arise from a single species or from different genera and/or species. Extensive research has been carried out over the years in an attempt to understand the biogenesis of naturally occurring enantiomers; however, many fascinating puzzles and stereochemical anomalies still remain.

Current knowledge on exocrine glands in carabid beetles: structure, function and chemical compounds

Many exocrine products used by ground beetles are pheromones and allomones that regulate intra- and interspecific interactions and contribute to their success in terrestrial ecosystems. This mini-review attempts to unify major themes related to the exocrine glands of carabid beetles. Here we report on both glandular structures and the role of secretions in carabid adults, and that little information is available on the ecological significance of glandular secretions in pre-imaginal stages.