How spruce budworm Choristoneura fumiferana detoxify plant host toxins

The spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), is one of the destructive insect species of the boreal forest in eastern North America. Recent studies have discovered two sets of phenolic compounds that appear to play an important role in the resistance of coniferous trees to the spruce budworm. The phenolic glycosides, picein and pungenin are present in most of the susceptible white spruce trees, but their aglycone forms, piceol and pungenol are found only in white spruce trees resistant to the spruce budworm. These compounds have been shown to retard development time, reduce budworm survival and pupal mass. This research focused on monitoring the fate of these phenolic aglycones (acetophenones) after ingestion by the budworm and aimed at determining how the compounds were detoxified. High performance liquid chromatography-mass spectrometry identified glycosylated and glutathionylated-metabolite of piceol and pungenol in the frass of the caterpillars. Midgut enzyme assays were conducted at neutral and alkaline pH to measure the activity of detoxification enzyme glutathione-S-transferase. \nIn this study, spruce budworm larvae were reared on either artificial diet only (control diet) or artificial diet containing combined acetophenones (piceol and pungenol). Our results suggest that the insects upregulated production of the detoxifying enzyme, glutathione-S-transferase, in response to feeding on diet containing acetophenones. The acetophenones were thus detoxified by conversion to glycosylated and glutathionylated form in the gut.