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.

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Secretions of an eversible gland on the metathorax of larvae of Chlaenius cordicollis Kirby (Coleoptera: Carabidae) are investigated by headspace analysis using solid phase microextraction followed by gas chromatography‐mass spectrometry (GC‐MS). Larvae from Manitoba, Canada and Pennsylvania, U.S.A., are sampled. Nine presumed defensive compounds are detected when the gland is everted, and this represents the first characterization of defensive secretions of larvae of a carabid beetle. With the exception of a single component (2‐methoxy‐4‐methylphenol), these compounds are distinct from those found in the defensive secretion of adult C. cordicollis. However, seven are more oxidized versions of the alkylphenolic compounds secreted by adult beetles: three hydroquinones (hydroquinone, methylhydroquinone and 2,3‐dimethylhydroquinone) and four quinones (p‐benzoquinone, toluquinone, 2,3‐dimethylquinone and ethyl‐p‐benzoquinone). An additional alkoxyphenol (2‐methoxy‐4‐ethylphenol) is also detected. Two patterns of composition are observed: in one, p‐benzoquinone and hydroquinone are undetectable and the ratio of toluquinone : 2,3‐dimethylquinone is 1 : 4.6 ± 0.6 (mean ± SE); in the other, all nine compounds are detectable and the ratio of toluquinone : 2,3‐dimethylquinone is 1 : 1.0 ± 0.2. These differences in pattern do not appear to be related to geographical source, sex or age of the larvae.