Tetranychus urticae long a cosmopolitan, and T. kanzawai originally limited to the Far East now occurs widely on a variety of horticultural crops in Japan. The latter also depends on wild host plants and there are frequent exchanges of individuals between crops and wild hosts. The two species have many host plants in common and show similar ecological performance. However, the host adaptability of T. kanzawai often differs among mite strains, forming host races, but not in T. urticae. In warmer areas of Japan, the distribution of T. urticae in the field is limited and the mites maintain their populations only if adequate hosts are available in both summer and winter. The incidence of diapause of T. urticae shows a latitudinal cline and in warmer areas the mites have very weak diapause. By contrast, populations in warmer areas, such as Kagoshima and Taiwan, of T. kanzawai show a high incidence of diapause. We then speculated the origin of the two spider mite species.

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The presence of the alarm pheromone was demonstrated in the hexane extract of an acarid mite Tyroborus lini Oudemans 1924. The active fraction derived from an SiO₂ column chromatography of the mite extract was identified as neryl formate, (Z)-3,7-dimethyl-2,6-octadienyl formate by GC/MS and GC analysis. The synthesized neryl formate was shown to be active at 0.05–1 ng dose. Males contained 0.08 ng of the compound on average, and females 0.16 ng on average. The alarm pheromone was a component present in the opisthonotal gland. Once totally discharged from the gland upon disturbance, it took seven days before the pheromone content reached to its original level in the gland, whereas other compounds recovered within 60 hrs. The reason remains obscure at present.

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A phytophagous mite species of the genus Tenuipalpus Donnadieu was found on 2 plant species, namely Nebelia sp. and Berzelia sp., imported from South Africa and intercepted by plant quarantine inspectors at Narita Airport, Japan. This mite is described and illustrated here as Tenuipalpus masakii sp. nov. The species is assigned to a unique aberrans species group having 3 pairs of nonflagellate caudolateral setae on the opisthosomal dorsum.

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Sennertia (Eosennertia) bifida, a new subgenus and species of Sennertia (Acari, Chaetodactylidae) is described from Japan based on the deutonymphs found on three Japanese species of the small carpenter bees, Ceratina japonica, C. flavipes and C. okinawana (Hymenoptera, Apidae). The new subgenus is quite different from the other known subgenera in possessing 5 pairs of unusual, apically bifid setae on idiosomal dorsum, and in having only one and no seta on tibiae I–II and femur IV, respectively. The other immature stages and adult are unknown.

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Amblyseius womersleyi is a native phytoseiid mite in Japan, and one of the promising natural enemies to control spider mites. A. womersleyi populations were collected from various region of Japan, and reproductive characteristics of the populations were compared to detect the intra-specific variation as a first step to establish high reproductive strains. Although the number of eggs produced by females copulated once did not vary among populations, the total number of eggs produced by females with supplementary copulation and the number of eggs produced daily by females copulated once and with supplementary copulation were significantly different. The mortality during immature development, the sex ratio in offspring when emerged and the prey consumption rate by gravid females also showed significant differences. The daily egg production was correlated with the total egg production, and highly correlated with the prey consumption rate. Consequently, A. womersleyi showed intra-specific variation of reproductive characteristics.

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