REPRODUCTIVE INTERFERENCE BETWEEN PANONYCHUS-MORI YOKOYAMA AND PANONYCHUS-CITRI (MCGREGOR) (ACARI, TETRANYCHIDAE) IN PEACH ORCHARDS

The reproductive interference between Panonychus mori YOKOYAMA and P. citri (McGREGOR) was studied in peach orchards, where they coexisted. The abundance of the two species differed greatly among individual pea ch trees, but the seasonal population trends were similar to each othe r: populations remained at very low densities from May to July, and th ereafter began to increase, reaching peaks in October. Ineffective fem ales (females that produced no female offspring), resulting from the i nterspecific matings between the two species, were observed in both sp ecies on the trees where they coexisted. The degree of reproductive in terference varied depending on the ratio of the densities of the two s pecies on individual trees, and was higher on P. mori by P. citri than vice versa. Furthermore, the proportion of females from overwintered eggs of P. mori collected from trees with a mixture of the two species was very low. These results seem to partially explain why P. mori can not extend its distribution to lower latitudes where climatic conditio ns are favorable for the species.