No abstract

In order to develop an artificial habitat encouraging the colonization efficiency of phytoseiid mites on fruit trees, we conducted choice experiments with a predacious phytoseiid mite, Neoseiulus californicus, using 22 types of artificial microstructures (3 cmϫ3 cm, less than 1 cm thick) in the laboratory. Large numbers of N. californicus preferred finetextured urethane foam and a shading net, although the locations where N. californicus settled on each microstructure were different: more than 80% of N. californicus adults preferred being 'on a plastic board under fine-textured urethane foam', while more than 95% preferred being 'on and in the shading net itself'. With respect to their practical use on fruit trees, shading nets are useful, because their size and thickness can be changed easily and they are also effective tools to transfer phytoseiid mites to trees with low phytoseiid densities. Thus, shading nets were considered to be the best candidate for an artificial habitat of phytoseiid mites on fruit trees.

We investigated the overwintering sites of the predacious mite Neoseiulus californicus in two satsuma mandarin orchards on Jeju Island, Korea, in February 2008. Our objectives were to improve the biological control strategy with N. californicus in perennial crops and to develop effective methods for examining the overwintering situations of N. californicus in the field. Nearly all specimens of N. californicus collected in the orchards were adult females, and the numbers of adult males and juveniles were very low. Most N. californicus were collected on herbaceous plants on the ground rather than on satsuma mandarin trees or woody plants surrounding the orchards. Among herbaceous plant species, higher densities of N. californicus were consistently found on species with rosette-type leaves compared to those with non-rosette-type leaves. Our results suggest that rosette-forming herbaceous plants are effective overwintering sites for conserving N. californicus in orchards. Furthermore, these plants would also provide useful sites for examining the potential overwintering situations of N. californicus in the field.

No abstract

Phyto traps were attached to twigs, main branches and trunks of Japanese pear trees in central Japan in autumn of 2004, to evaluate the effectiveness of the trap as a tool to study overwintering phenology of arboreal phytoseiid mites. A subset of the traps was inspected and replaced at two-weeks intervals ("short-term Phyto trap"), in order to evaluate movement of phytoseiid mites on the trees in a short-term. The remaining traps were left undisturbed and collected monthly from January to May 2005 ("long-term Phyto trap"), to know what species overwinter in the traps and when they leave them. Most phytoseiid mites were collected in the traps on twigs. The most abundant phytoseiid species was Typhlodromus vulgaris Ehara. In the short-term traps on twigs, adult females and males of T. vulgaris were collected until mid-November 2004, when the pear trees became completely defoliated, but few mites were collected from December to April. On the other hand, adult females of T. vulgaris were abundant in the long-term traps on twigs sampled from January to April, but other stages of mites were never collected. These results indicate that T. vulgaris had moved to the long-term traps by late November, and that only adult females had overwintered in the traps. These females began to move and reproduce in early May. By that time immature developmental stages of T. vulgaris were also recorded in the short- and long-term Phyto traps. Our results confirmed that the Phyto trap was a useful tool for estimating overwintering phenology of phytoseiid mites on trees.

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.

Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) is an effective predator of spider mites. In Korea, it is distributed on Jeju Island, but is never found further north on the mainland. Due to poor natural control of spider mites by native predatory mites in mainland orchards, commercialization of the Jeju Island strain of N. californicus on the mainland is currently being considered. We conducted two field experiments in mainland apple orchards during winter 2008 and 2009 to assess the effects of sheltered ground habitats on the overwintering potential of N. californicus. In the first experiment, all of the N. californicus individuals that were experimentally placed on bare ground died within 27 days, whereas 70% of mites sheltered by fallen apple leaves or urethane foam survived for more than 27 days. In the second experiment, individuals were released directly onto the ground, either with or without urethane foam. More individuals were found within urethane foam plots than in plots without foam. Sheltered ground habitats would be an important factor for N. californicus when selecting overwintering sites, and could eventually lead to enhanced winter survival. On the other hand, no live N. californicus individuals were found by the end of the winter in either experiment, which suggests that N. californicus could not successfully overwinter in the study area, even in sheltered ground habitats.

No abstract