Defensive Secretions of the Carabid Beetle Chlaenius cordicollis: Chemical Components and their Geographic Patterns of Variation

Abstract

The defensive secretion of the ground beetle Chlaenius cordicollis is predominantly 3-methylphenol. Adult C. cordicollis were collected in Pennsylvania and Manitoba and induced to discharge defensive secretion in a vial. The headspace was sampled by solid phase microextraction, and samples were analyzed by gas chromatography-mass spectrometry. Five alkylphenolic compounds were detected: all beetles secreted 3-methlyphenol, 2,5-dimethylphenol, and 3-ethylphenol, and most beetles from each locality secreted detectable amounts of 2,3-dimethlyphenol and 3,4-dimethylphenol. In about 80% of beetles, we detected small amounts of the alkoxyphenolic compounds 2-methoxy-4-methylphenol and 2-methoxy-5-methylphenol. Multivariate compositional analysis of relative peak areas of alkylphenolic compounds revealed geographic variation and sexual dimorphism in defensive secretions. Compared with samples from Manitoba, relative peak areas of samples from Pennsylvania were lower for 2,3-dimethylphenol and higher for 3-methylphenol. Sexual dimorphism was detected only in Manitoba where, compared with samples from males, relative peak areas for samples from females were higher for 2,5-dimethylphenol and lower for 3-ethylphenol. This is the first report of geographic variation in defensive secretions of carabid beetles, and it demonstrates the need for knowledge of patterns of variation before characterizing the defensive secretions of a species as a whole.

Defensive secretions of larvae of a carabid beetle

“…With the exception of 2‐methoxy‐4‐methylphenol, the compounds found in the samples from larvae are not detected in the defensive secretions of adult C. cordicollis (Holliday et al , ). However, the larval compounds are chemically related to those found in the adult secretion, which is dominated by 3‐methylphenol and contains smaller quantities of four additional alkylphenolic compounds: 2,3‐dimethylphenol, 2,5‐dimethylphenol, 3,4‐dimethylphenol and 3‐ethylphenol (Holliday et al , ). The first five compounds listed in Table , comprising more than 93% of the total peak area from larval headspace samples, are more oxidized forms of these alkylphenolic compounds.…”

“…A blank was also obtained by exposing a SPME fibre in a vial that did not contain a larva. All SPME fibres were analyzed in Pennsylvania; a previous study (Holliday et al , ) has established that shipping conditions do not affect the detected chemical composition.…”

“…The main component of the adult defensive secretion is 3-methylphenol (Eisner et al, 1963). The identification of minor components of the defensive secretion of adult C. cordicollis, including alkylphenolic and alkoxyphenolic compounds, is reported by Holliday et al (2012).…”

Chemical diversity and potential biological functions of the pygidial gland secretions in two species of Neotropical dung roller beetles

“…Many beetle species secrete a variety of compounds from pygidial glands, compounds which have multiple functions in nature and have been the subject of numerous studies (Pasteels et al 1983;Witz and Mushinsky 1989;Kanehisa and Tsumuki 1996;Schultz and Puchalski 2001;Attygalle et al 2004;Francke and Dettner 2005;Holliday et al 2012;Schierling et al 2012). These compounds comprise a wide range of volatiles including carboxylic acids, carbonyl compounds, and alcohols, as well as simple aromatic compounds, derivatives of amino acids and hydrocarbons (Classen and Dettner 1983;Davidson et al 1989;Kelley and Schilling 1998;Will et al 2000;Francke and Dettner 2005;Lusebrink et al 2008).…”

“…Solvent extraction of dissected glands is a frequently used standard method (Moore and Brown 1971;Attygalle et al 2004;Francke and Dettner 2005;Bonacci et al 2011;Holliday et al 2012;Schierling et al 2012). However, it is not optimal for sample preparation, because large amounts of body lipids are carried out as contaminants and these may interfere with the separation steps that follow.…”