Can the population size of Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) on Japanese pear trees be estimated by Phyto traps attached to the twigs?

Abstract

The Phyto trap is an artificial microstructure that permits the easy collection of live predacious phytoseiid mites in the field. Neoseiulus californicus is a well-established indigenous phytoseiid mite in Japanese pear tree orchards in Japan. We examined whether or not the population size of N. californicus on Japanese pear trees can be estimated using Phyto traps attached to twigs in two Japanese pear orchards. The results suggest that the density of a prey mite, Tetranychus kanzawai, on leaves influenced the number of N. californicus trapped by the Phyto traps. When the density of T. kanzawai was high on the leaves, many N. californicus were observed on the leaves and the pattern of density change synchronized between T. kanzawai and N. californicus. Under this condition, no N. californicus were found in the Phyto traps. On the other hand, when the density of T. kanzawai was low on the leaves, N. californicus were found in the Phyto traps as well as on the leaves. The number of N. californicus collected by the Phyto traps also increased as the extent of leaf withering increased, and reached a peak after leaf fall was complete. This suggests that the movement of N. californicus on the pear trees during leaf-fall season can be elucidated in some detail by using the Phyto trap. The survey by the Phyto trap attached to twigs can eventually clarify the population fluctuation and movement of N. californicus on trees that are been overlooked in the investigation of the leaves alone.