Within-tree variation in density and survival of leafminers on oak Quercus dentata.
The density and survival of leafminers were examined on 50 sun leaves from each of 65 Quercus dentata individuals in Hokkaido, northern Japan during 1997-98. Phyllonorycter (two species), Caloptilia (one species) and Stigmella (three species) were abundant or common on this oak in the study area. These leafminers appeared after mid-June, whereas most externally feeding caterpillars occurred from late May to early June when the water content and nitrogen concentration of leaves were high. The density of these leafminers was about four times higher in 1998 than in 1997. A negative correlation was more often observed between mine density and leaf size, leaf wet weight per area or leaf toughness in the Phyllonorycter species, but the opposite correlation was more frequent for Caloptilia and Stigmella species. Conversely, no clear relation was observed between the survival of Phyllonorycter larvae and leaf traits. In all leafminers except the gregarious Stigmella species, the mine density was more often positively correlated with leaf damage by chewing insects, and also the survival of Phyllonorycter larvae was often positively correlated with leaf damage. In the Phyllonorycter species, the survival of larvae tended to increase with the increase in density at the autumn generation. The correlation in the densities of mines between the summer and autumn generations was more frequently positive in the Phyllonorycter and Caloptilia species. In addition, the densities of different leafminers were often positively correlated. Thus, relations among leafminers, between leafminers and externally feeding caterpillars, and also between herbivores and host plants are complicated.