Influence of food and larval age on the defensive chemistry of Saturnia pyri

Scolus secretions and hemolymph of caterpillars of Saturnia pyri fed with t wo different foodplants (Crataegus monogyna. Prunus spinosa) were chemicall y analyzed and their chemical similarities determined. The secondary-compou nd patterns obtained for the two body fluids showed no significant differen ces when compared between the two groups of alternatively fed last-instar l arvae. Thus, the composition of these fluids of full-grown caterpillars is not influenced by the larval diet. However, younger larvae on P. spinosa re vealed a diversity of compounds differing significantly from that of larger caterpillars fed with either C. monogyna (both body fluids) or P. spinosa (hemolymph only). This indicates that, on the one hand, the hemolymph compo sition is adapted to the changing physiological requirements of the given i nstars whereas, on the other hand, the defensive mixtures remain unaltered in the late larval instars due to a constant spectrum of potential enemies.