Masatoshi Toyama’s research while affiliated with National Agriculture and Food Research Organization and other places

Our earlier study revealed that pesticide use considering the preservation of phytoseiid mites is crucially important for the effective utilization of commercialized Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) release materials for spider mite control in Japanese pear orchards. Pesticide use alteration corresponding to commercialized N. californicus release material installation might change phytoseiid mite species composition and affect the efficacy of commercialized N. californicu s in spider mite control. This study evaluated the effect of pesticide use alteration on phytoseiid mite species composition and subsequent spider mite control using commercialized N. californicus at Japanese pear orchards. We examined the population dynamics of spider mites and phytoseiid mites in Japanese pear orchards during 2019–2023. In 2022 and 2023, commercialized N. californicus release materials were installed at a Japanese pear orchard under conditions limiting the use of pesticides with adverse effects on phytoseiid mites. The results demonstrated that the most dominant species was shifted from N. californicus to Amblyseius eharai Amitai et Swirski (Acari: Phytoseiidae) with no significant suppression effects of commercialized N. californicus in spider mite control. The results also demonstrated a decline in the distribution of commercialized N. californicus to pear leaves. Amblyseius eharai and indigenous N. californicus dominantly existed in that order before commercialized N. californicus distribution to pear leaves. These results suggest that intraguild predation by A. eharai and competition with indigenous N. californicus might be involved in the less efficient distribution of commercialized individuals as major and minor factors, respectively.

This study explores sustainable agricultural practices by examining the role of organic materials in enhancing native predatory mites for controlling spider mites in apple orchards. Developing techniques to conserve indigenous natural enemies is vital for sustainable agricultural production. Phytoseiid mites can control spider mites, which are among the most significant pests in apple production. To conserve phytoseiid mite populations, it is important to identify alternative prey and to determine their role in phytoseiid mite proliferation. We demonstrated that the concurrent use of specific organic fertilizers and coconut husks can increase prey Tyrophagus mites, thereby enhancing phytoseiid mite density. Our research was conducted using sticky traps at the Miyagi Prefectural Agriculture and Horticulture Research Center in Japan. The occurrence of Tyrophagus mites was significantly correlated with the occurrence of phytoseiid mites in 2 years. In laboratory experiments, the use of organic fertilizers increased the density of Tyrophagus mites by 83 × within 4 weeks. Several species of phytoseiid mites were able to lay between 0.25 and 1.03 eggs per day per female by preying on Tyrophagus larvae. A 2-year field survey revealed that the use of organic fertilizers more than doubled the density of phytoseiid mites on apple leaves, likely through promoting Tyrophagus mite proliferation on the ground. These results highlight the potential of organic fertilizers not only to enhance soil nutrients, but also to boost phytoseiid mite populations, thereby contributing to more sustainable apple production.

Animal-mediated pollination is an essential ecosystem service for the production of many fruit trees. To reveal the community composition of flower-visiting wild insects which potentially contribute to fruit production and to examine the effects of geographic location, local meteorological conditions and locally introduced domesticated pollinators on them, we investigated the community composition of insects visiting the flowers (hereafter, “visitors”) of apple, Japanese pear and Oriental persimmon for 1‒3 years at 20 sites around Japan. While most of the variation (82%) of the community composition was explained by tree species with a slight contribution by geographic distance (2%), maximum temperature and tree species contributed 62% and 41% of the variation in total abundance of the visitors, respectively. Though the dominant families of the visitors varied spatiotemporally, the community composition of the visitors of apple and Japanese pear clearly differed from that of Oriental persimmon. While Andrenidae and Syrphidae together accounted for 46%‒64% of the visitors of apple and Japanese pear, Apidae represented 57% of the visitors of Oriental persimmon. The taxonomic richness, diversity and evenness of the visitors were best predicted by locally introduced domesticated pollinators and local meteorological conditions of wind speed and maximum temperature. Amongst these selected factors, locally introduced domesticated pollinators could have the largest impact. It seemed to be strongly related to the reduction of taxonomic richness, diversity and evenness of the visitors, accounting for 41‒89% of the variation. Results suggested that the community composition and total abundance of potential pollinators were predominantly determined by tree species and temperature, but locally introduced domesticated pollinators could have a determinantal pressure on the taxonomic diversity of the community.

A series of monitoring of insects visiting crop flowers was conducted on several crop species around Japan. The project, which ran from 2017 to 2021, was led by NARO and funded by the Japanese Ministry of Agriculture, Forestry and Fisheries (MAFF) to determine the abundance and diversity of wild insects that could potentially contribute to crop production across Japan. Flower-visiting wild insects were captured using plastic vials during the blooming season at multiple sites for one to several years. Domesticated pollinators, Apis mellifera and Osmia cornifrons were also captured in 2017. This data includes more than 6,500 individuals of flying insects from 18 families of Hymenoptera, 33 families of Diptera, 17 families of Coleoptera, Hemiptera, Lepidoptera, Psocodea, and Neuroptera captured in 20 fields of apple (Malus pumila Mill.), Japanese pear (Pyrus pyrifolia (Burm.f.) Nakai), and Oriental persimmon (Diospyros kaki Thunb.) as of August 2023.

A report of our earlier study described a phytoseiid mite Neoseiulus californicus (McGregor) (Acari: Phytoseiidae) release system using a moisturized sheltered sachet for spider mite control. For the present study, we installed the predator release systems on 43 out of 71 trees in a Japanese pear orchard to survey the dispersal of N. californicus released from the predator release system. In the orchard, Japanese pear trees were trained on the overhead horizontal trellis system. Consequently, the trees were mutually connected through the trellis training system. We collected phytoseiid mites on the tree leaves and were subjected to PCR to examine their species composition. Results demonstrated that N. californicus were 62.37% of the total of 3,247 phytoseiid mites collected. Using microsatellite markers, commercialized N. californicus that had been released from the predator release systems were discriminated from indigenous N. californicus. Results demonstrated that phytoseiid mites consisting mainly of the commercialized N. californicus occurred one week earlier in trees with the predator release systems. Results also demonstrated that the commercialized N. californicus dispersal occurred mainly in trees installed with the predator release systems.

The pollination services provided by small wild pollinators in apple orchards were investigated in Akita Prefecture, northern Japan. In the apple orchard in 2017 and 2018, wild species constituted about 43% of all pollinators collected; these wild pollinators belonged to the order Hymenoptera (with most in the families Andrenidae [Andrena spp.] and Halictidae [Lasioglossum spp.]) and the order Diptera (mainly Melanostoma spp.). To exclude the introduced bees Apis mellifera and Osmia cornifrons, we protected flower bud clusters with 3.5-mm-mesh net bags that allowed access only to small wild pollinators from 2019 to 2021. There was no significant difference between protected and unprotected king flowers in terms of fruit set or the number of ventricles with seeds in the king fruits. Moreover, significantly fewer lateral fruits, which need to be removed by thinning, set in the protected clusters. These observations indicated that apple fruits might set normally without the need for introduced pollinators, and in some cases introduced bees might promote fruiting beyond the capacity of labor to manage.

The toxicity of 85 insecticides, 20 acaricides, 70 fungicides, and 15 spreaders was tested against the predatory mite, Neoseiulus californicus（McGregor）（Acari: Phytoseiidae）. Four neonicotinoids, 1 sulfoximine, 2 pyridine azomethine derivatives, 2 Bacillus thuringiensis and the insecticidal proteins they produce, 6 benzoylureas, 1 buprofezin, 3 diacylhydrazines, 1 oxadiazine, 1 semicarbazone, 6 diamides, flonicamid, pyridalyl, flometoquin, 9 acaricides, 4 spiracle-blocking insecticides, 52 fungicides, and 13 spreaders were harmless to the survival of adult females and immature individuals. These pesticides had little effect on the survival of adult females but 2 neonicotinoids, 1 semicarbazone, flometoquin, 3 acaricides, 2 spiracle-blocking insecticides, 11 fungicides, and 4 spreaders reduced the fecundity. The residual toxicity of 7 insecticides, 6 acaricides, and 5 fungicides were examined against the adult females. These pesticides could be divided into 3 groups: Group A（materials that were harmful as less than 14-day-old residues）: fenitrothion, imidacloprid, spinosad, spinetoram, emamectin, milbemectin, bifenazate, and pyflubumide＋ fenpyroximate, Group B（materials that were harmful as 14- to 21-day-old residues）: thiamethoxam, spirotetramat, etoxazole, propineb, mancozeb, and chinomethionat, and Group C（materials that were harmful as 21- to 28-day-old residues）: amitraz, pyridaben, thiophanate-methyl, and diethofencarb＋thiophanate-methyl.

Cultivated Japanese pear varieties, mostly showing self-incompatibility, require pollen transfer from other varieties. To elucidate the underlying mechanisms of open Japanese pear insect pollination, we first collected flower-visiting insects using plastic vials and sticky traps in orchards located at different regions in Japan. Results showed that insects assigned to the families Andrenidae (Hymenoptera), Apidae (Hymenoptera), Halictidae (Hymenoptera), Syrphidae (Diptera) and Empididae (Diptera) are abundant in the orchards. Second, we restricted the flower-visiting insects to access Japanese pear flowers using bags with mesh sizes of 0, 2 and 3.5 mm. Results indicated that insects which allowed to pass through bags with 3.5-mm mesh size but not through bags with 2-mm mesh size contribute primarily to pollination, represented as the fruit-set ratio and seed number. Third, we measured head and thorax widths of the flower-visiting insects and counted pollen grains on their body surfaces to estimate their pollination potential. Results indicated that insects assigned to the families Andrenidae, Halictidae, Syrphidae, Bibionidae (Diptera) and Muscidae (Diptera), including species with both widths smaller than 3.5 mm, harbour large quantities of Pyrus pollen grains, in addition to Apis mellifera (Apidae) with both widths greater than 3.5 mm. Consequently, the families Andrenidae, Apidae, Halictidae and Syrphidae might be the most important insect families for Japanese pear pollination. However, species identification of the flower-visiting insects showed no common key species that contribute remarkably to pollination services other than A. mellifera. Consecutive insect collection using plastic vials and sticky traps demonstrated that compositions of the flower-visiting insects are fluctuating continuously in the orchards. Nevertheless, year-to-year fluctuation of the fruit-set ratio was less pronounced in open-pollinated orchards than in hand-pollinated orchards. These results suggest that mutual complementation among diverse pollinator species might be the mechanism underlying open Japanese pear insect pollination.

The toxicity of 29 fungicides was tested against 4 native phytoseiid species, namely, Amblyseius eharai Amitai and Swirski, Amblyseius tsugawai Ehara, Euseius sojaensis（Ehara）, and Typhlodromus vulgaris Ehara（Acari: Phytoseiidae）, which are abundantly found in fruit tree orchards in Japan. Mancozeb and propineb were toxic to the immature individuals of all 4 species and to the fecundity of adult females of E. sojaensis and A. eharai. Thiuram was harmless or slightly toxic to A. eharai, A. tsugawai, and T. vulgaris, whereas it was toxic to E. sojaensis. Sulphur and polyoxin were toxic to the immature individuals of all four species. Benomyl and thiophanate-methyl reduced the fecundity of A. eharai, A. tsugawai, and E. sojaensis. Fluazinam was toxic to immature individuals and the fecundity of adult females of E. sojaensis and moderately toxic to A. eharai and A. tsugawai. Iminoctadine triacetate was toxic to immature individuals of E. sojaensis. Fluoroimide was also moderately toxic to immature individuals of E. sojaensis. On the other hand, basic copper sulfate, oxine-copper, captan, chlorothalonil, iminoctadine tris（albesilate）, dithianon, difenoconazole, hexaconazole, imibenconazole, tebuconazole, fluopyram, inpyrfluxam, isopyrazam, penthiopyrad, pyraziflumid, cyprodinil, kresoxim-methyl, pyribencarb, and trifloxystrobin were harmless to all 4 species.