Enzyme activity modification in adult beetles (Agelastica coerulea) inhabiting birch trees in an ozone-enriched atmosphere.

Tropospheric ozone (O3) is a naturally occurring gas in the atmosphere. However, the concentration of O3 increased in the twentieth century. Although the effects of O3 on vegetation have been extensively studied since the 1950s, limited information exists regarding the effects of O3 on insect herbivores. In particular, evidence is lacking regarding the effects of O3 on the biology of insect herbivores. Agelastica coerulea Baly (1874) is a coleopteran species that grazes on Betulaceae plants. In this study, to investigate the effects of O3 on A. coerulea biology for the first time, female adult insects were collected from Japanese white birch trees grown in a Free Air Controlled Exposure System (FACE) in Sapporo, Japan. These beetles inhabited trees exposed either to ambient or to elevated O3 for 23 days. After collection, the enzyme activities in the beetles were measured. Elevated O3 led to a greater total antioxidant activity and lower α- and ß-esterase activities, a phenomenon that may suggest an increased resistance of the beetles to stress. Our results are further discussed with regard to biological and toxicological aspects. Collectively, our findings indicate that total antioxidants and α- and ß-esterase activities can serve as effective O3 biomarker systems in this beetle species. This adaptive response of the beetle, which was induced by moderate O3 exposure, should be further tested across generations and for its protection against greater exposure.

Growth and nutrition of Agelastica coerulea (Coleoptera: Chrysomelidae) larvae changed when fed with leaves obtained from an O3-enriched atmosphere.

A series of laboratory no-choice assays were performed to test changes in the feeding, growth, and nutrition of leaf beetle (Agelastica coerulea) larval instars on O3-treated leaves of Japanese white birch (Betula platyphylla var. japonica). Larvae fed with O3-treated leaves grew and developed significantly faster throughout their developmental cycle than the corresponding controls. The growth rate (GR) and consumption index (CI) were mostly decreased with age for both control and O3-treated leaves. Efficiency of conversion of both ingested and digested food (ECI, ECD) showed an increase from the 2nd to the 4th instar, after which they decreased significantly and reached the lowest value in the last larval instars (7th). GR, CI, ECI, and ECD were greater and approximate digestibility (AD) was lower in larvae fed with O3-treated leaves than those fed with control leaves. This indicated that the greater rate of growth on fumigated leaves was due primarily to a greater rate of consumption (i.e., O3 increased the "acceptability" of the host more than "suitability") and efficiency in converting food into body mass. Overall, larval performance seemed to have improved when fed with O3-treated leaves in these assays. This study suggests that insects may be more injurious to O3-treated plants and warrants further investigations on birch-beetle interactions under field conditions.

Ozone alters the feeding behavior of the leaf beetle Agelastica coerulea (Coleoptera: Chrysomelidae) into leaves of Japanese white birch (Betula platyphylla var. japonica).

High mixing ratios of ground-level O3 threaten trophic interactions. In the present study, we conducted laboratory assays, where insect larvae and adults were not directly exposed to O3, 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 O3 levels. We found that overwintered adults were not deterred from grazing elevated O3-treated leaves, but rather preferred them than ambient O3-treated ones. We also found that the feeding behavior of 2nd instar larvae fed on early or late leaves was not influenced by the O3 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 O3-enriched atmosphere. Since adults preferred elevated O3-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.