Host plant and field density of <i>Tetranychus phaselus</i> Ehara (Acari: Tetranychidae)

Abstract

Tetranychus phaselus (Acari: Tetranychidae) lives chiefly on the mulberry weed Fatoua villosa (Moraceae), and reaches high densities in the autumn. To test the prediction that T. phaselus is adapted to F. villosa, we investigated the suitability of six host plants available in this species' habitat. We supplementarily investigated the association between the density of T. phaselus and the density of an important predatory mite, Neoseiulus womersleyi (Acari: Phytoseiidae) on F. villosa leaves to infer the predation pressure. To know the characteristics of host plant use in T. phaselus, these characteristics were compared with the population of the common polyphagous species T. kanzawai on ramie (Boehmeria nivea, Urticaceae) leave. With respect to host-plant suitability, T. phaselus had one of the highest egg production and the survival rate on F. villosa among all six host plants examined, which partly supports the prediction that T. phaselus is adapted to F. villosa. On the other hand, T. phaselus egg production and development time on F. villosa was similar to that of T. kanzawai reared on F. villosa. Nevertheless, T. phaselus was found only on F. villosa in the field, and the density per leaf area of T. phaselus on F. villosa was higher than that of T. kanzawai on ramie leaves. Considering that the density of N. womersleyi was not significantly associated with the density of T. phaselus, the high density of T. phaselus could be partly attributed to the scarcity of N. womersleyi on F. villosa leaves.