Detoxification of host plant phenolic aglycones by the spruce budworm

Abstract

This study examines the post-ingestive fate of two host-plant derived small-molecule phenolics (the acetophenones piceol and pungenol) that have previously been shown to be toxic to the outbreaking forest pest, spruce budworm ( Choristoneura fumiferana ). We test first whether these compounds are transformed during passage through the midgut, and second whether the budworm upregulates activity of the detoxification enzyme glutathione-s-transferase (GST) in response to feeding on these compounds. Insects were reared on either foliage or artificial diet to the fourth instar, when they were transferred individually to one of two treatment diets, either control or phenolic-laced, for approximately 10 days, after which midguts were dissected out and used for Bradford soluble protein and GST enzyme activity analysis. Frass was collected and subjected to HPLC-DAD-MS. HPLC showed that the acetophenones do not autoxidize under midgut pH conditions, but that glucose- and glutathione- conjugates are present in the frass of insects fed the phenolic-laced diet. GST enzyme activity increases in insects fed the phenolic-laced diet, in both neutral pH and alkaline assays. These data show that the spruce budwom exhibits counter-adaptations to plant phenolics similar to those seen in angiosperm feeders, upregulating an important detoxifying enzyme (GST) and partially conjugating these acetophenones prior to elimination, but that these counter-measures are not totally effective at mitigating toxic effects of the ingested compounds in the context of our artifical-diet based laboratory experiment.

Defensive Traits during White Spruce (Picea glauca) Leaf Ontogeny

“…Indeed, some compounds decrease as expected with leaf expansion (e.g., total phenolics, alkaloids, d-3-carene), while others, by contrast, increase (e.g., total monoterpenes, acetophenones). However, the defensive role of these compounds remains poorly defined, especially given that many specialist herbivores, including the spruce budworm, possess effective detoxification enzymes [ 69 ]. It must be noted that many of these compounds could also be implicated in plant metabolism in roles other than anti-herbivore defense and these other roles might determine their seasonal time course.…”

Plant Allelochemicals as Sources of Insecticides

“…Nevertheless, physiological adaptations of specialist insects cope with plant defenses. Specialists that rely on plant secondary metabolites as attractants and feeding stimulants can be negatively affected by plant defenses, in some cases simply via energy that is required for detoxification [32]. However, on average, specialist herbivores are less negatively affected by defense compounds than generalists.…”

Gene selection for studying frugivore-plant interactions: a review and an example using Queensland fruit fly in tomato

“…The genes identified through this process were associated with different phases of the insect chemical-detoxification process, which occurs for both the detoxification of plant secondary chemicals and pesticides (Heidel-Fischer & Vogel, 2015;Heckel, 2018). During Phase I, genes/enzymes such as P450 monooxygenases (P450s) and carboxylesterases (COEs) are involved in oxidation, hydrolysis or reduction of toxic compounds; subsequently, Phase II involves the conjugation of the modified toxins with hydrophilic groups such as glutathiones, sulphate and sugars by glutathione S-transferases (GSTs) and UDP-glucosyltransferase (UGT) to enhance the polarity of the molecules and so help excretion; while finally, in Phase III, ATP-binding cassette transporters export the conjugated toxins out of the cell (Donkor et al, 2019). Each phase of the detoxification process is associated with major gene families (Fig.…”