Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2002
Publication Date: 1/20/2003
Citation: Southwell, I.A., Russell, M.F., Maddox, C.A., Wheeler, G.S. 2003. Differential metabolism of 1,8-cineole in insects. Journal of Chemical Ecology. 29:83-94. 2003.
Interpretive Summary: The terpenoid compound, 1, 8-cineole is one of the most common and toxic substances present in Melaleuca and Eucalyptus foliage. However, several insect species feed upon leaves rich in this substance without any ill effects. These insects breakdown this compound and excrete altered forms of the original compound. These altered forms or metabolites, usually excreted in the insect frass, were described in order to determine how these species feed and develop on these plants with apparent impunity. The insect species studied include the chrysomelid beetles Faex nigroconspersa, Chrysophtharta bimaculata, the pyrgo beetle Paropsisterna tigrina. Additionally, metabolites were identified from the Leichhardt's grasshopper Petasida ephippigera and the melaleuca snout weevil Oxyops vitiosa. The insect species studied generally attach a single, or in the case of O. vitiosa two, OH on specific locations on the parent molecule. The structures of the metabolites, their retention times on four different stationary phases, and mass spectral data are provided. This information assists scientists interested in identifying the means by which these species metabolize this potential toxicant.
Technical Abstract: In order to answer questions posed by the metabolism of 1, 8-cineole in pyrgo beetle, Paropsisterna tigrina, three other herbivorous insects species, Faex nigroconspersa, Chrysophtharta bimaculata and Oxyops vitiosa were fed 1, 8-cineole leaf diets. F. nigroconspersa, adults excreted predominantly 9-hydroxy-1, 8-cineole (8) (36.2% of the volatile constituents) with some 2 alpha-hydroxy-1, 8-cineole (2) (11.4%). In contrast, the larvae excreted predominantly 2 alpha-hydroxy-1, 8-cineole (2) (27.4%) and smaller proportions of 9-hydroxy-1, 8-cineole (8) (5.2%) and 3 alpha-hydroxy-1, 8-cineole (4) (4.3%). C. bimaculata adults excreted predominantly 3 alpha-hydroxy-1, 8-cineole (4) (16.5%). Oxyops vitiosa adults, on a lower 1, 8-cineole diet, excreted predominantly 2 alpha, 9-dihydroxy-1, 8-cineole (9) (4.2%) and 2 alpha-hydroxy-1, 8-cineole (2) (3.5%) with smaller proportions of 3 alpha-hydroxy-1, 8-cineole (4) (1.1%) and 9-hydroxy-1, 8-cineole (8) (0.5%). This is the first reported occurrence of a dihydroxycineole as an insect metabolite. Gas chromatographic and mass spectral data for hydroxycineoles are recorded and interspecific metabolite variation discussed.