New defensive chemical data for ground beetles (Caleoptera : Carabidae): interpretations in a phylogenetic framework

First reports of major defensive chemicals for ground beetles representing four tribes include: Morionini (formic acid), Dercylini (methacrylic and ti glic acids), Catapiseini (formic acid and decyl acetate) and Perigonini (fo rmic acid and decyl acetate). Multiple species from Loxandrini were sampled and, shown to contain formic acid, not salicylaldehyde as previously repor ted. Several hexenoic acid compounds were found in the clivinine genus Schi zogenius representing a third class of chemicals for that tribe. Salicylald ehyde was found for the first time in a species of Oodini. Additional speci es from Pterostichini: Patrobini and Odacanthini were sampled and the resul ts were found to be consistent with previously published reports. The taxon omic distribution of defensive secretions is reviewed for tribes across the family Carabidae. The simultaneous occurrence of hydrocarbons and formic a cid is noted in phylogenetically more derived carabids. By mapping chemical classes onto a phylogenetic hypothesis, it is shown that formic acid or ot her relatively strong irritants are correlated with tribes having a high sp ecies diversity in tropical regions, whereas tribes exhibiting higher diver sity in temperate regions use milder saturated/unsaturated carboxylic acids . Based on this phylogenetic interpretation, the evolution and maintenance of formic acid is interpreted as the result of predation pressures and poss ibly the evolution of chemical mimicry. (C) 2000 The Linnean Society of Lon don.