There are many related studies; however, almost all of them focus on higher taxonomic tendencies, ignoring a difference in the reaction for each species. In this study, we measured relative basal area (RBA) as the index for invasion of broad-leaved trees into eight Larch plantations, and investigated the relationship between RBA and composition and abundance of oribatid mites community. As a result, we found 49 families, 60genus, 89 species, 24,368 adult and larvae and nymphs, 56,364. The degree of invasion of broad-leaved trees did not affect significantly total abundance and number of species for oribatid mites observed. While, those measurements significantly correlated with the total amount of litter, including conifer and broad-leaves. We also found that there are many oribatid mite species showing habitat preference relating to a kind of litter.

Tetranychus evansi Baker & Pritchard occurs on solanaceous plants, and causes serious damage to various crops in Africa and Europe. Tetranychus takafujii Ehara & Ohashi was found on Solanum nigrum L. in Japan in 2001 and described as a new species in 2002. However, because T. takafujii is very similar to T. evansi in morphology, doubt has arisen about the difference between these two species, although there is no report discussing their taxonomic status. Tetranychus takafujii is specialized on solanaceous plants and it is possible that this species gets out of hand after invasion of solanaceous agricultural crops. To evaluate its potential severity as a pest, it is necessary to assess its performance on a variety of food plants in a carefully controlled laboratory set-up. The present study determined the development on 21 crops and weeds, and the reproduction on Solanum nigrum of a Japanese T. takafujii population and six T. evansi populations from abroad. Four plants (potato, horsenettle, pear and cucumber) served as host plant for all seven populations and most larvae successfully reached adulthood. Life-history parameters, such as the rate of development and the intrinsic rate of natural increase (rm), became higher with temperature increasing from 15 to 35°C. The rm-value at 25°C was similar among all populations tested and it was close to the value obtained in T. takafujii [Kotsubo et al. (2004) J. Acarol. Soc. Jpn. 13: 71-76]. This indicates that T. takafujii has the potential to become a serious pest on solanaceous crops, just the same as T. evansi in Africa and Europe.