美佐子 三島

Dimorphism of Leaf Galls Induced by Pseudasphondylia neolitseae (Diptera: Cecidomyiidae) on Neolitsea sericea (Lauraceae) and Their Distributional Patterns in Kyushu, Japan

Pseudasphondylia neolitseae (Diptera: Cecidomyiidae) induces two different types of gall (upper and lower types) on the leaves of Neolitsea sericea (Lauraceae). In the upper type, the adaxial side of the gall projects more prominently than the abaxial side, and vice versa in the lower type. The lower type galls were found mainly in northwestern and northern Kyushu, while the upper type were found mainly in southwestern and southern Kyushu and their distributional patterns were parapatric with a little overlapping. The coexistence of both types on a single host tree was relatively rare. Whenever they coexisted on a single tree, they always appeared together on the same leaf, although the relative abundance of one type to another was biased toward one side. The ploidy level of host plants was not related to the gall types, because almost all host trees examined were diploid. Therefore, the gall types are not determined by the differentiation of ploidy level of host plant, and possibly determined by the gall midge. The parapatric distribution pattern of the two gall types may suggest that P. neolitseae is now entering into the initial stage of speciation, if gall dimorphism leads to reproductive isolation.