GENETIC-STUDIES ON THE DIAPAUSE OF THE 2-SPOTTED SPIDER-MITE TETRANYCHUS-URTICAE KOCH (2)

The genetic basis of diapause of Tetranychus urticae KOCH was analyzed by crossing experiments at 3 temperature conditions, using one diapausing strain (D), which exhibited nearly 100 percentage of diapause, and 2 non-diapausing strains (ND), which completely lacked diapause. F1 hybrids between D and ND1, which was selected from a population in Ibaraki, exhibited more than 80% diapause regardless of the direction of the crosses and temperatures, suggesting "diapause" was fully dominant over "non-diapause". On the other hand, the incidence of diapause of F1 hybrids between D and ND2, which was selected from a population in Nara, declined sharply with increasing temperature. It also differed greatly depending on the direction of the crosses, showing that a maternal effect was operating. Backcrosses of F1-hybrids to parental strains showed that "non-diapause" was under polygenic control. Several nucleo-cytoplasm hybrids were established by repeated backcrosses using D and ND strains. Diapause incidence of F1-hybrids between the nucleo-cytoplasm hybrids and their parental strains showed that cytoplasmic factors were involved in diapause suppression, explaining the maternal effect shown in reciprocal crosses.