Population dynamics of leafminers on a deciduous oak Quercus dentata

Population dynamics of leafminers on a deciduous oak Quercus dentata, were studied for 9 years in northern Japan. Most leafminers in the study site were bivoltine, while a gregarious Stigmella species was univoltine. Many leafminers showed species-specific patterns of population fluctuations. In the major bivoltine leafminers (Phyllonorycter, solitary Stigmella and Caloptilia species), the densities of autumn generation mines were highly correlated with those of summer generation mines when analysed on the basis of the densities at the early developmental stage. Thus, their mortality and egg productivity in this phase (i.e., from late June to early September) varied only a little from year to year. In Phyllonorycter, however, correlation of densities between these two generations became lower when analysed on the basis of the densities at the tissue-feeding stage, suggesting that their mortality from the early developmental stage to the tissue-feeding stage in the autumn generation varied from year to year. Regression analyses suggest that yearly variation in precipitation in July and August was responsible for this variation. Correlations of densities between the autumn generation and the summer generation of the next year in the major leafminers were not high. Thus, their mortality and/or egg productivity in this phase (i.e., from September to June of the next year) varied from year to year. Regression analyses suggest that climatic factors that affected the population dynamics in this phase varied among the leafminers, except some factors have been suggested to be commonly effective in the two Phyllonorycter species. Density-dependent effects were not explicit in the population dynamics of the present leafminers.