Differential Metabolism of 1,8-cineole in Insects

In order to compare the metabolism of 1,8-cineole in the pyrgo beetle, Paropsisterna tigrina, three other herbivorous insect 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 (36.2% of the volatile constituents) with some 2alpha-hydroxy-1,8-cineole (11.4%). In contrast, larvae excreted predominantly 2alpha-hydroxy-1,8-cineole (27.4%) and smaller proportions of 9-hydroxy-1,8-cineole (5.2%) and 3alpha-hydroxy-1,8-cineole (4.3%). C. bimaculata adults excreted predominantly 3alpha-hydroxy-1,8-cineole (16.5%). Oxyops vitiosa adults, on a lower 1,8-cineole diet, excreted predominantly 2alpha,9-dihydroxy-1,8-cineole (4.2%) and 2alpha-hydroxy-1,8-cineole (3.5%), with smaller proportions of 3alpha-hydroxy-1,8-cineole (1.1%) and 9-hydroxy-1,8-cineole (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.