Guild Structure of Gall Midges on Fagus crenata in Relation to Snow Gradient: Present Status and Prediction of Future Status as a Result of Global Warming

Abstract

Twenty six species of gall midges (Diptera: Cecidomyiidae) induce leaf galls onFagus crenata. Because the adult life span of gall midges is very short, they must emerge and oviposit in the short period of a specific stage of budburst.Fagus crenatais mainly distributed in regions with heavy snowfall. Snow cover prevents the emergence of gall midges that overwinter on the ground as immature stages. Therefore the time of snow melt in relation to that of budburst is likely to be an important factor determining the success of gall midges. The species number and density of theFagusgall midges tend to be higher in intermediate snowfall areas, in which snow covers the ground surface throughout the winter but the time of snow melt is earlier than that of budburst. The gall midge fauna is known to be poor inF. crenataforests with little snowfall because of desiccation during the winter. As a result of global warming, the distribution range ofF. crenatawill shift to regions with higher elevation and/or higher latitude although the rate of this vegetation shift is considered to be slower than that of temperature change. We hypothesize that theFagusgall midge fauna will become richer in the short term becauseF. crenataforests with intermediate snowfall will increase by the global warming. However, in the long term, the gall midge fauna will become poorer following the retrenchment ofF. crenataforests