Secretion of the ventral glands in Craesus sawfly larvae

The secretion from ventral glands of Craesus alniastri, Craesus septentrionalis, and Craesus latipes (Hymenoptera, Tenthredinidae, Nematinae) was analysed by GC–MS. The terpenoid dolichodial was the major compound in the three species. A few other terpenoids, several hydrocarbons, esters, aldehydes, and the aromatic compound benzaldehyde were also detected. Among the Nematinae the occurrence of dolichodial is restricted to Craesus and several species of the closely related genus Nematus. Craesus comprises approximately 20 species. Their larvae are generally gregarious and brightly coloured, and they possess highly developed ventral glands. Field tests show that the gregarious habit of C. septentrionalis larvae is an active process. This manuscript covers the chemotaxonomy, biosynthesis and bioactivity of dolichodial, and the interactions between glandular secretion and appearance of larvae.