Herbicide Stress Modifies Defensive, Nutritional, and Volatile Chemistry of Red Maple Cultivars Associated with...

Herbicide exposure can alter plant secondary metabolism with consequences for insect host selection, yet its effects on volatile organic compound (VOC) signaling remain poorly understood. Red maple (Acer rubrum L.) is a widely planted ornamental tree frequently attacked by flatheaded borers (Chrysobothris spp.), and herbicide injury has been associated with increased borer activity. We investigated how trunk application of two commercial herbicides, one contact herbicide (pelargonic acid) and one systemic herbicide (glyphosate), influence VOC emissions and associated nutritional and defensive chemistry in two red maple cultivars differing in susceptibility to Chrysobothris. Across a four-week field experiment, foliar VOCs were quantified alongside sugars, polyphenols, and tannins, and related to borer oviposition attempts and larval success. Herbicide exposure induced compound-specific and cultivar-dependent VOC responses, with the susceptible cultivar ('Brandywine') exhibiting greater temporal variability and elevated emissions of select monoterpenes, including β-myrcene. These VOC shifts coincided with increased foliar polyphenols and trunk sugar concentrations. In contrast, the less susceptible cultivar ('Autumn Blaze') showed comparatively stable chemical profiles across treatments. Oviposition attempts and larval occurrence were concentrated on herbicide-treated 'Brandywine' trees, particularly following contact herbicide exposure. Together, these results suggest that herbicide-induced modulation of VOC signaling, coupled with changes in nutritional and defensive chemistry, may influence adult host selection, larval performance following oviposition, and ultimately enhance host suitability and apparency to Chrysobothris.