Emerald ash borer attacks trees revealing early chemical clues

Abstract

The Emerald Ash Borer (EAB), Agrilus planipennis, is a major global forest pest (a buprestid beetle) that has decimated ash trees (Fraxinus species) throughout Europe and Asia. Since this nonnative invasive insect was introduced into the U.S. in the early 1990s (near Detroit Michigan), it has spread rapidly to at least 35 US states and five Canadian provinces, killing billions of ash trees in North America over the past 30 years. The small green-metallic adult females lay eggs in bark crevices which hatch to produce larvae that penetrate into the phloem and outermost rings of the sapwood to create extensive galleries (borer canals) as they feed. These galleries block the flow of vital carbohydrates and nutrients to the roots which slowly weakens the tree, causing gradual defoliation and ultimately death. Discriminate factor analysis aroma plots revealed differences in sample types at four EAB-infestation levels. Early infestations begin in the upper tree trunks and are not obvious because it takes up to a year or more before symptoms start appearing and the characteristic D-shaped adult emergence holes are visible. Consequently, control treatments cannot be applied early enough before substantial damage to trees has already occurred. The search for new methods to detect EAB infestations of ash trees at early stages, before visible indicators appear, led to the present discovery that larval feeding disrupts normal metabolic pathways of living tissues and cause the release of abnormal volatile organic compound (VOC) emissions, providing early chemical indicators of infestations. Effects of EAB-infestations on host metabolic processes, associated with levels of tissue damage by gallery formation and symptom severity, were shown from analyses of VOC emissions from sapwood cores taken from green ash trees at four different levels of attack. The well-defined infestation levels were based on an increasing scale of visible tree damage. The capabilities of detecting visually hidden EAB galleries at early stages of tree infestations with this new pest-management tool provide more effective means for planning and implementing targeted EAB pest-suppression and forest management activities, including establishing quarantines in high-hazard areas.

Citation

Wilson, Alphus D. 2023. Emerald ash borer attacks trees revealing early chemical clues. Atlas of Science 2023(3):1-3.