Hybridization experiments among 5 strains of lesteri as interstrain crosses and between 4 strains of sinensis and 2 strains of lesteri as interspecific crosses were performed. All the strains used originated from different localities in Japan. Results of interstrain crosses of lesteri indicated that reproductive isolation does not exist among the strains of this species. The fact that sinensis and lesteri co-exist in Japan from north to south and retain their identities is by itself evidence that they are true biological species. Reproductive isolation due to hybrid inviability and complete chromosomal asynapsis of the F1 hybrids between sinensis and lesteri confirm this, while synaptic x chromosomes were exceptionally found in a few cases of the F1 hybrids. Many similarities in banding patterns of the salivary chromosomes observed in the F1 hybrids and their parental species indicate a close relationship.
