Does Ozone Alter the Attractiveness of Japanese White Birch Leaves to the Leaf Beetle Agelastica coerulea via Changes in Biogenic Volatile Organic Compounds (BVOCs): An Examination with the Y-Tube Test

Elevated ground-level ozone (O-3) reduced C-based defense chemicals; however, severe grazing damages were found in leaves grown in the low O-3 condition of a free air O-3 -concentration enrichment (O-3-FACE) system. To explain this phenomenon, this study investigates the role of BVOCs (biogenic volatile organic compounds) as signaling compounds for insect herbivores. BVOCs act as scents for herbivore insects to locate host plants, while some BVOCs show high reactivity to O-3, inducing changes in the composition of BVOCs in atmospheres with elevated O-3. To assess the aforementioned phenomenon, profiles of BVOCs emitted from birch (Betula platyphylla var. japonica Hara) leaves were analyzed ex situ, and Y-tube insect preference tests were conducted in vitro to study the insect olfactory response. The assays were conducted in June and August or September, according to the life cycle of the adult alder leaf beetle Agelastica coerulea Baly (Coleoptera: Chrysomelidae). The Y-tube tests revealed that the leaf beetles were attracted to BVOCs, and O-3 per se had neither an attractant nor a repellent effect. BVOCs became less attractant when mixed with highly concentrated O-3 (>80 ppb). About 20% of the total BVOCs emitted were highly O-3-reactive compounds, such as beta-ocimene. The results suggest that BVOCs emitted from the birch leaves can be altered by elevated O-3, thus potentially reducing the attractiveness of leaves to herbivorous insects searching for food.