Age- and sex-related variation in defensive secretions of adult <Emphasis Type="Italic">Chlaenius cordicollis</Emphasis> and evidence for their role in sexual communication

Defensive secretions of adult Chlaenius cordicollis (Coleoptera: Carabidae) from Manitoba and Pennsylvania were analyzed across the life cycle in a multi-year study using solid phase microextraction and gas chromatography-mass spectrometry. In concurrent experiments using Y-tube olfactometry, we observed the response of each sex when male or female source beetles were induced to discharge defensive secretions. Almost all defensive secretion samples contained five alkylphenolic compounds, dominated by 3-methylphenol; frequently, two alkoxyphenolic compounds and one ester were also detected. As beetles aged, the composition of their defensive secretion shifted, showing an exponential decrease in the relative proportion of 2,3-dimethylphenol as a function of day of year. Previously reported differences observed in autumn between secretions of beetles from Manitoba and Pennsylvania are attributable to different times of onset of the decline of 2,3-dimethylphenol in the two locales. Regardless of airborne odor, responding beetles exhibited upwind anemotaxis in the olfactometer and, outside of the reproductive period, avoidance was the most frequent response to defensive secretions. Sexual dimorphism was evident in the major components of the defensive secretions during the reproductive period and resulted from an increase over time in 2,5-dimethylphenol in male beetles. In the reproductive period, neither sex avoided odor from male source beetles, females preferred clean air to odor from source females, and males were attracted to females that discharged defensive secretion but showed no preference when females had not discharged the secretion. The defensive secretion appears to function as a sex attractant during the reproductive period.