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.
Highlights
In the chemical arms race between plants and herbivores, insects exhibit multiple mechanisms for dealing with plant secondary metabolites in their diet, ranging from avoidance, rapid egestion, enzymatic detoxification via degradation or conjugation, or even sequestration for use in defense [1]
Comparison of HPLC-DAD-MS chromatograms of acetophenones incubated at neutral and alkaline pH suggests that these compounds do not autoxidize under alkaline conditions
Previous work suggests that the phenolics of Picea abies, unlike those of many angiosperms, show only minor changes under alkaline incubation [26]
Summary
In the chemical arms race between plants and herbivores, insects exhibit multiple mechanisms for dealing with plant secondary metabolites in their diet, ranging from avoidance, rapid egestion, enzymatic detoxification via degradation or conjugation, or even sequestration for use in defense [1]. Insect counter-defenses are often phenotypically plastic, especially in generalist feeders, and induced by plant compounds in the diet. These counter-adaptations to plant defenses can occur at different time points: before ingestion, in the digestive tract prior to absorption or within cells afterwards [2,3]. By a Concordia University Dean’s Award of Excellence to D.D. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
