Molecular verification of dispersal of phytoseiid mites from groundcover plants to tree leaves in Japanese peach orchards

A population survey of phytoseiid mites and of spider mites on randomly selected trees and their groundcover plant Paederia foetida L. (Rubiaceae) was conducted in Japanese peach orchards that used different pesticide practices. An organic orchard with wild groundcover and no synthetic chemicals used for pest control and a conventionally managed orchard with bare ground had no trees on which spider mite density was beyond the control threshold density (one mite per leaf). On the other hand, spider mite densities in some trees at conventionally managed orchards with wild groundcover were temporary beyond the control threshold level. The phytoseiid mite species composition on peach leaves estimated by previously established method using quantitative sequencing changed during the survey period and varied among orchards. PCR amplification of the internal transcribed spacer (ITS) region of ribosomal genes of Tetranychus kanzawai Kishida and Panonychus mori Yokoyama from three phytoseiid mite species, Neoseiulus californicus (McGregor), Amblyseius eharai Amitai and Swirski, and Euseius sojaensis (Ehara), collected on peach leaves was conducted. Results showed that the feeding preference for the three phytoseiid mite species was greater for T. kanzawai than for P. mori in the field. PCR amplification of the ITS sequences of Petrobia harti (Ewing) inhabiting Oxalis corniculata L. (Oxalidaceae) showed that phytoseiid mites move from groundcover plants to peach leaves, possibly through ambulatory and aerial dispersal.