Pattern analysis of galling host-plants in Taiwan

Three hundred and thirty-one species of galling hosts, including 86 endemic and 15 exotic plant species were investigated and collected in Taiwan. Among these records, 317 species are dicotyledons, comprising more than 90% of the total host-plant species, including 86 (7.6%) endemic species and 15 (2.3%) exotic species. To test the plant family hypothesis, regression analysis of plant family size and gall richness was conducted. No significant relationship was found between family size and gall richness which may have been caused by the effect of dominant galling hosts. The regression analysis on native, endemic, and exotic host species with gall diversity indicated the highest trend in endemic hosts. Another analysis showed that gall richness was different between herbs and woody hosts censused. Insect groups exploring endemic and exotic species tended to differ in that 157 morphospecific gallers were found on endemic species and 14 on exotic species. Most host-plants bore a single type of gall each species, and only 39.1% had more than 2 types. The top five most frequently occurred endemic hosts are Machilus (Lauraceae) and 77.1% of the gallers were Cecidomyiids. The result suggests that in-host speciation may have occurred in the Cecidomyiidae on Machilus.

Key words: insect gall, host-plant, endemic species, non-endemic native species, exotic species.