Genetic Compatibility Among Diapausing Red, Non-Diapausing Red and Diapausing Green Forms of the Two-Spotted Spider Mite, Tetranychus urticae KOCH (Acari : Tetranychidae)

The occurrence of diapause and reproductive compatibility were studied among three different forms of the two-spotted spider mite, Tetranychus urticae KOCH, found in Japan. The three forms were the diapausing red (DR) form (first described here), the non-diapausing red (NDR) form (formerly called T. cinnabarinus (BOISDUVAL)) and the green (G) form. Almost all DR and G females entered diapause, whereas females from NDR completely lacked diapause. The bean and the kudzu vine were suitable hosts for all three forms, but the carnation and the transvaal daisy were suitable only for the NDR and DR forms, respectively. Thus, the host plant spectrum of each form was different. In intra-population crosses, all populations produced both female and male progeny. Inter-population crosses within the same forms also resulted in the production of both sexes, suggesting that these populations were compatible. However, no fertile F_1 females were produced in crosses between DR and either NDR or G, indicating that the former was reproductively incompatible with the latter two. On the other hand, NDR mites produced a smaller number of fertile F_1 and F_2 females when mated with G mites, showing that gene exchange between them is possible. Thus, it seems that NDR and G are conspecific, although they show severe genetic incompatibilities.