Chemical basis of unwettability in Liacaridae (Acari, Oribatida): specific variations of a cuticular acid/ester-based system

After chemo-metamorphosis: p-menthane monoterpenoids characterize the oil gland secretion of adults of the oribatid mite, Nothrus palustris

The oil gland secretion of the oribatid mite Nothrus palustris is known to show the phenomenon of juvenile-adult polymorphism, i.e., juvenile instars produce secretions predominated by geranial, whereas adults secrete dehydrocineole along with a number of chemically unidentified compounds. We here re-analyzed the secretions of adult N. palustris by GC-MS and NMR spectroscopy, eventually identifying the unknown compounds as p-menthane monoterpenoids. The major components were two isomeric 6-isopropenyl-3-methyl-cyclohex-3-en-1-yl formates (= p-1,8-menthadien-5-yl formates), which accounted for about 75% of the secretion. These were accompanied by five additional, only partly identified p-menthanes (or p-methane-derivatives), all of which represented minor or trace components. In addition, adult secretions contained two C21-hydrocarbons, 1,12-heneicosadiene (major) and a heneicosatriene (minor). Menthane monoterpenoids represent a novel sub-class of terpene compounds in the oil gland secretions of Oribatida. In case of N. palustris, we assume that both geranial and p-menthane monoterpenoids arise via the mevalonate pathway which obviously shows a split at the level of geranyl pyrophosphate, leading to geranial in juveniles and to p-menthanes in adults. The significance of methane occurrence in oil glands as well as the taxonomic distribution of juvenile-adult polymorphism in oribatid oil gland secretions is discussed. The latter phenomenon-i.e., "chemo-metamorphosis" of secretions-is not known from early- and middle-derivative Oribatida nor from Astigmata, but appears to be more common in some derivative desmonomatan and brachypyline oribatid groups.

The scent gland chemistry of Gagrellinae (Opiliones, Sclerosomatidae): evidence for sequestration of myrmicacin in a species of Prionostemma

The scent gland secretion of an undetermined species of Prionostemma from Costa Rica was analyzed by gas chromatography–mass spectrometry and shown to consist of medium-chain carboxylic acids (mainly octanoic acid) and a ß-hydroxy-carboxylic acid, eventually identified as myrmicacin (= (R)-3-hydroxydecanoic acid). While scent gland secretions in harvestmen have traditionally been considered to be products of de novo synthesis, we here provide evidence for the unusual case of sequestration-derived scent gland constituents: at least myrmicacin appears to be sequestered from leaf-cutter ants that constitute a part of the prey of the Prionostemma-species herein investigated. This is the first report on the scent gland chemistry of the sclerosomatid subfamily Gagrellinae as well as on a possible sequestration mechanism in harvestmen.

Identification of saturated and unsaturated 1-methoxyalkanes from the Thai millipede Orthomorpha communis as potential "Raincoat Compounds"

Mixtures of saturated and unsaturated 1-methoxyalkanes (alkyl methyl ethers, representing more than 45.4% of the millipede hexane extracts) were newly identified from the Thai polydesmid millipede, Orthomorpha communis, in addition to well-known polydesmid defense allomones (benzaldehyde, benzoyl cyanide, benzoic acid, mandelonitrile, and mandelonitrile benzoate) and phenolics (phenol, o- and p-cresol, 2-methoxyphenol, 2-methoxy-5-methylphenol and 3-methoxy-4-methylphenol). The major compound was 1-methoxy-n-hexadecane (32.9%), and the mixture might function as “raincoat compounds” for the species to keep off water penetration and also to prevent desiccation.

Comparative chemical analysis of army ant mandibular gland volatiles (Formicidae: Dorylinae)

Army ants are keystone species in many tropical ecosystems. Yet, little is known about the chemical compounds involved in army ant communication. In the present study, we analyzed the volatile mandibular gland secretions—triggers of ant alarm responses—of six Neotropical army ant species of the genus Eciton (outgroup: Nomamyrmex esenbeckii). Using solid-phase microextraction, we identified 12 chemical compounds, primarily ketones with associated alcohols, one ester and skatole. Most compounds were shared among species, but their relative composition was significantly different. By comparing chemical distances of mandibular gland secretions to species divergence times, we showed that the secretions’ compositions are not strictly determined by phylogeny. By identifying chemical bouquets of seven army ant species, our study provides a valuable comparative resource for future studies aiming to unveil the chemicals’ precise role in army ant alarm communication.

Storage and release of hydrogen cyanide in a chelicerate (Oribatula tibialis)

Cyanogenesis denotes a chemical defensive strategy where hydrogen cyanide (HCN, hydrocyanic or prussic acid) is produced, stored, and released toward an attacking enemy. The high toxicity and volatility of HCN requires both chemical stabilization for storage and prevention of accidental self-poisoning. The few known cyanogenic animals are exclusively mandibulate arthropods (certain myriapods and insects) that store HCN as cyanogenic glycosides, lipids, or cyanohydrins. Here, we show that cyanogenesis has also evolved in the speciose Chelicerata. The oribatid mite Oribatula tibialis uses the cyanogenic aromatic ester mandelonitrile hexanoate (MNH) for HCN storage, which degrades via two different pathways, both of which release HCN. MNH is emitted from exocrine opisthonotal oil glands, which are potent organs for chemical defense in most oribatid mites.

Scent of a mite: origin and chemical characterization of the lemon-like flavor of mite-ripened cheeses

Cheese infested with cheese mites is usually treated as unpalatable. Nevertheless, some traditional cheese manufactories in Germany and France intentionally use mites for fermentation of special varieties (i.e. Milbenkäse and Mimolette). While their production includes different mite species, both are characterized by a "lemon-like" flavor. However, the chemical nature and origin of this flavor-component is unknown. The cheese mites possess a pair of opisthosomal glands producing blends of hydrocarbons, terpenes and aromatics. Here, we describe the chemical profiles of the astigmatid mite species Tyrolichus casei (Milbenkäse) and Acarus siro (Mimolette). Although the chemical profiles differ in several aspects, both mite species produce neral (a volatile flavor component of lemon oil), which was absent from the headspace of both cheeses without mites. We conclude that the lemon-like flavor of mite cheese is not a consequence of fermentation of the cheese itself but a component from secretions of the cheese mites.