Abstract
Similar nest-weaving habits, sociality characterize all the species belonging to the recently reinstated spider mite genus Stigmaeopsis. Molecular phylogenetic analysis using 28S rDNA shows that Stigmaeopsis forms a distinct clade and that there is another unrecognized clade involving Schizotetranychus species with comparable nest-weaving habits distributing in tropical regions. Furthermore, the phylogenic hypothesis suggests that Stigmaeopsis miscanthi (Saito) inhabiting Miscanthus sinensis Anderss. shared a common ancestor with Stigmaeopsis longus (Saito) inhabiting Sasa senanensis (Franch. et Sav.), both mite species having very similar social systems. We confirmed reproductive isolation between them and tested the suitability of the two plant species as hosts for these two mite species. The result that S. miscanthi immatures could survive on Sasa bamboo for a long period, but S. longus immatures could not survive on Miscanthus grass suggested that the former has evolved from a common ancestor living on Sasa bamboo. This is also supported by a third piece of indirect evidence obtained from observing mite responses to the plant-originated chemical cues involving feces used for waste management in these species. Therefore, we conclude that the host plant shift of S. miscanthi from Sasa bamboo to M. sinensis played a key role in speciation.