To obtain selective pesticides that are harmless to the predatory mite, Neoseiulus longispinosus, native to Thailand, we tested the toxicity of 29 pesticides on the predatory mite by the leaf-dip method. All pesticides were examined at the concentrations used in the fields of Thailand. The results immediately after dipping the leaf in pesticide showed that fenbutatin oxide, buprofezin, fenobucarb, imidacloprid, dinotefuran, validamycin, carbendazim and sulfur were selective pesticides, harmless to adult females, eggs and immatures of N. longispinosus. These chemicals are expected to be promising pesticides on IPM crops in Thailand, where N. longispinosus is the major natural enemy of spider mites.

We studied the distribution of the predatory phytoseiid mite, Neoseiulus longispinosus (Evans), in Thailand. The predator was distributed over the entire areas of the country throughout the year. It was found on 33 plant species ranging from perennial plants such as fruit trees to annual crops such as vegetables and ornamentals. N. longispinosus was abundant on plants infested with spider mites producing heavy webbing on the lower surface of leaves.

Specific adaptation of sympatric populations of the Kanzawa spider mite, Tetranychus kanzawai (Acari: Tetranychidae) to three host plants. Ryusen TAJIMA, Kazunori OHASHI and Akio TAKAFUJI (Laboratory of Ecological Information, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan)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.

No abstract

We used two types of molecular markers to analyze the genetic structure of seven populations of Tetranychus kanzawai complex collected from the Tohoku area of northern Honshu, the main island of Japan. For phylogenetic analysis, we used DNA sequences of the mitochondrial cytochrome oxidase subunit I (COI) gene and the internal transcribed spacer 1 (ITS1) region of the ribosomal RNA gene; for detailed analysis of population structure, we used microsatellite markers. We found that all population pairs were differentiated significantly; this differentiation was enhanced significantly by host plant effect but not by geographic distance among the populations. DNA sequencing of ITS1 and COI regions and microsatellite analysis both showed that the population occurring on Pueraria lobata was deviated genetically from the other populations. Therefore, our analysis suggested that population subdivision in T. kanzawai complex developed because of host plant effects rather than geographic barriers.