High mixing ratios of ground-level O threaten trophic interactions. In the present study, we conducted laboratory assays, where insect larvae and adults were not directly exposed to O, to test the feeding behavior and attraction of the coleopteran leaf beetle Agelastica coerulea to early and late leaves of Japanese white birch (Betula platyphylla var. japonica) treated with ambient or elevated O levels. We found that overwintered adults were not deterred from grazing elevated O-treated leaves, but rather preferred them than ambient O-treated ones. We also found that the feeding behavior of 2nd instar larvae fed on early or late leaves was not influenced by the O treatment of the leaves when larvae could choose leaves. These observations of the adults and larvae feeding preferences contradict prior observations in the field conditions where the insects avoided leaves in O-enriched atmosphere. Since adults preferred elevated O-exposed leaves in the present laboratory assays, it is worthy of further investigations whether adults change their grazing preference so as to ensure the leaf palatability as a feeding source for their larvae. Hence, new direction towards detailed ovipositional behavior surveys under field conditions is encouraged.

Ground-level ozone (O 3 ) increases yearly and negatively affects the growth of birches via leaf dynamics. Leaf area is directly related to plant production and is usually reduced by elevated O 3 (eO 3 ) and insect herbivores. The objective of this study was to explore factors affecting change in leaf number of white birch saplings and insects grazing under eO 3 . In order to accomplish this objective, we observed seasonal changes in leaf phenology and determined foliar defense chemicals in saplings grown under ambient air and free-air O 3 enrichment (60 nmol mol -1 for daytime). The leaf phenology showed the total number of emerged leaves was about 10 per shoot in the control and eO 3 plots. However, the number of attached leaves per shoot at ambient air decreased after mid-July, probably due to grazing by larvae of the leaf beetle. In addition, the concentration of condensed tannin in early leaves was higher in the eO 3 plot than that in the control plot. Such leaves with decreased nutritional value under eO 3 may prevent feeding of leaf beetles. These findings lead to the plausible understanding of an indirect effect of eO 3 on leaf phenology via foliar defense of white birch against insect herbivores.