What physiological processes permit insects to eat Eucalyptus leaves?

Many species of insects eat Eucalyptus foliage despite its relatively low n utritional value and the many plant secondary metabolites (PSMs) present, f or example, terpenes, phenols and formylated phloroglucinols (FPGs). Formyl ated phloroglucinols are a new class of PSMs that act as antifeedants for p ossums and koalas. What physiological processes are present that permit ins ects to eat eucalypt foliage and how do PSMs influence insect feeding or di gestion? Some trees seem to be repeatedly infested with eucalypt-feeding in sects, possibly as a result of previous chemosensory cues remaining from pa rental selection of a plant. Avoidance or storage of PSMs permit jarrah lea fminers (Perthida glyphopa) and sawflies (Perga sp.) to consume eucalypt fo liage without dealing with the majority of these compounds. Some PSMs can b e metabolized by polysubstrate membrane oxidases as found in caterpillars o r sawflies that feed on eucalypts. High midgut pH may be advantageous for n utrient extraction and PSM metabolism, and midgut pH ranges between 8.5 and 8.9 for caterpillars of Hyalarcta huebneri. Plant secondary metabolites ma y not be absorbed as a result of the combined presence of the peritrophic m atrix and endogenous surfactants. Excretion of PSMs can be as metabolites o r intact compounds. Both putative metabolites and sideroxylonal-A, an FPG, are present in the faeces of larvae of the case moth, H. huebneri. The pres ence of sideroxylonal-A in the food had an effect on the presence of 5-hydr oxytryptamine (5HT) in the central nervous system of caterpillars, as larva e fed leaves with a high concentration of sideroxylonal-A had relatively mo re 5HT in the brain and central nervous system ganglia than larvae fed leav es containing a low concentration. Further work is necessary to clarify how PSMs are handled by eucalypt-feeding insects and what effect FPGs have on feeding and digestion.