THE SECRETION OF THE VENTRAL GLANDS IN HOPLOCAMPA SAWFLY LARVAE

The defensive secretion of the ventral glands of both species, Hoploca mpa testudinea and H. flava is mainly composed of acetogenins. Major c ompounds are (E)-2-octenal, (E,Z)- and (E,E)-2,4-decadienal and (E,Z,Z )-2,4,7-decatrienal that was identified for the first time in an insec t. Benzaldehyde is abundant in H. flava. A comparison of Hoplocampa wi th taxonomically related genera suggests that, for those acetogenins p resent as major compounds in the secretion, the chain length decreased during evolution of nematine sawflies. Only the last larval instar of Hoplocampa species produces large amounts of secretions. For H. testu dinea, the last instar as compared with previous ones was more efficie ntly protected against ants in a bioassay, and possessed allometricall y larger glands. Hoplocampa larvae live concealed within the fruit tha t they infest until dropping off the plant for pupation in the soil. T he relative importance during the ontogeny of the mechanical protectio n offered by the fruit and the chemical defence provided by the ventra l glands is discussed, also with respect to field observations on the interactions between ants and sawfly larvae. Our hypothesis is that ne matine sawfly larvae with a concealed life style will show a relative reduction in glandular size and defensive significance of the glandula r secretion. (C) 1997 Elsevier Science Ltd.