In our previous report, we showed that there is strong reproductive isolation between two groups of the subsocial spider mite species, Schizotetranychus miscanthi Saito. S. miscanthi can be distinguished into two groups by differences in male-to-male aggressiveness: one has high and the other has low male-aggression. In this paper, we studied in detail the pattern of reproductive isolation between these two groups. We found isolation to occur at two different stages. Namely, the first barrier decreased the rate of egg fertilization (pre-zygotic isolation) and the second one hindered immature development (post-zygotic isolation). However, we did not observe obvious depression of hatchability, which is often observed in spider mites. Furthermore, there were significant differences in the patterns of incompatibility between females originating from different localities, when they were crossed with males of the other aggression group.These differences in incompatibility patterns were unusual and have been difficult to explain so far. The factors that account for these differences in this spider mite is a problem for future studies.
2000 by the Japanese Society of Applied Entomology and Zoology