Growth retarding activity of lichen substances against the polyphagous herbivorous insect Spodoptera littoralis

Abstract

Fourteen frequently occurring lichen substances including two depsides, seven depsidones and four pulvinic acid derivatives as well as an anthraquinone, were studied for their influence on growth and development of polyphagus herbivore Spodoptera littoralis. Whereas larval survival was usually not affected most of the compounds studied caused a pronounced reduction of larval growth in chronic feeding experiments with neonate larvae. The ED 50s of the most active compounds oxyphysodic acid and vulpinic acid were 11.2 and 17.2 μmol g −1 dry wt., respectively whereas the natural concentrations of both compounds were 41 μmol g −1 dry wt. for the former (in Hypogymnia physodes) and 137 μmol g −1 dry wt. (in Letharia vulpina) for the latter. Several of the lichen compounds including oxyphysodic acid, fumarprotocetraric acid or calycin when fed to neonate larvae during the first 6 days of their development caused a pronounced increase of the larval period and/or a high incidence of developmental malformations in the resulting imagines, indicating deleterious long term effects of the respective compounds. The growth-retarding effects of oxyphysodic acid or norstictic acid towards larvae of S. littoralis were not restricted to the pure compounds but were also observed when crude lichen extracts were incorporated into artificial diet. However, lichens containing the depside atranorin or the anthraquinone parietin were usually more active than the pure compounds indicating the presence of so far unknown bioactive compounds in the respective extracts.