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We investigated the hypothesis that feeding deterrence of common ringtail possums (Pseudocheirus peregrinus) and common brushtail possums (Trichosurus vulpecula) by Eucalyptusterpenes (in this case 1,8-cineole) is a result of a conditioned flavor aversion (CFA), due to the association of terpenes with postingestive effects of another group of Eucalyptustoxins, the diformylphloroglucinol compounds (DFPCs). Wild-caught common ringtail and common brushtail possums showed a dose-dependent reduction in food intake when 1,8-cineole was added to the diet. However, after continued exposure over 12 days to increasing amounts of cineole in the diet, both species substantially increased their intakes of cineole relative to control animals. This indicated that the aversion to cineole was a conditioned response rather than a physiological limitation in their ability to detoxify terpenes. Subsequent exposure to a diet including both cineole and jensenone (a simple DFPC also found in Eucalyptusand considered to cause postingestive emesis) in corresponding amounts was able to recondition the dose-dependent aversion. Consequently, animals that had been given jensenone showed an aversion to cineole-rich diets that matched the behavior of animals in the control group. This supported our hypothesis that the effect of terpenes on feeding of these marsupial folivores on Eucalyptusis due to a CFA. Possums can cope with levels of terpenes in the diet that far exceed those occurring naturally. The role of terpenes in marsupial folivore–Eucalyptusinteractions appears to be to act as a cue to levels of toxic DFPCs in the leaves, rather than acting as toxins in their own right.

Eucalyptusdisplays strong intraspecific variation in resistance to browsing by marsupial folivores that can be attributed to variation in the concentration and type of diformylphloroglucinol compounds (DFPCs) in the foliage. In this study, we ask which functional groups of diformylphloroglucinol compounds determine their effectiveness in deterring feeding. We used a simple and highly deterrent compound, jensenone, as a model DFPC and compared its activity to structural variants that differ in the types of functional groups on the phloroglucinol molecule. Torquatone, a naturally occurring compound in the steam volatile fraction of Eucalyptus torquatafoliage, has neither the aldehyde nor phenol groups that are believed to contribute to the antifeedant actions of jensenone. From the naturally occurring compounds we have synthesized two intermediates, a capped phenol/free aldehyde compound (acetyl-jensenone) and a free phenol/no aldehyde compound (demethyl-torquatone). Addition of jensenone and acetyl-jensenone to diets of common ringtail possums (Pseudocheirus peregrinus) substantially reduced their food intakes. Torquatone showed less activity, and there was little reduction in food intake when demethyl-torquatone was added to the diet. We conclude that at least the aldehyde groups attached to the aromatic nucleus are important in determining whether these compounds deter feeding by common ringtail possums, whereas the phenol groups may play only a minor role.