Abstract
In order to elucidate whether the Kanzawa spider mite, Tetranychus kanzawai, adapts specifically to the host plant on which it occurs, we compared the adult maturation rate and oviposition rate in populations derived from Nerium indicum, Hydrangea macrophylla and Kerria japonica, on each host plant. The 3 host plants were growing within a short distance and therefore exchange of mite individuals was thought to be possible among them. In all 3 populations, the adult maturation rate was significantly larger on the plant they derived from than that on the other two plants. Each population also showed higher oviposition performance on the plant it derived from. In particular, although both species had toxic chemicals, the host adaptation of populations from N. oleander differed from that of populations from H. macrophylla: both the adult maturation rate and oviposition performance in the population from N. oleander were significantly lower on H. macrophylla than on N. oleander, and vice versa, showing a notable differentiation in host utilization ability between them. This suggested the existence of trade-offs in host adaptation between the two populations, and the possibility of sympatric host-race formation in this species.
