An inoculation test was performed with 9 cultivars of 4 species of Cucurbitaceae including “Kenkyaku” to select a test plant to be used for the pathogenicity test of Streptomyces sp., which causes root tumor of melon. The melon cultivar “New melon”, the cucumber cultivar “Suyo”, and the oriental pickling melon cultivar “Nagasaki tsukeuri” showed disease severity of approximately 80 relative to 100 for “Kenkyaku”. Of the 3 cultivars, “New melon” formed the largest number of root tumors. The pathogenicity test was performed on the hypocotyl tissue in seedlings of these cultivars by injecting the inoculum. Morphological abnormality was observed in the injected part 3 days after inoculation. Hypertrophy of the inoculated tissues was conspicuous in hypocotyls of “New melon” and “Nagasaki tsukeuri”. Root tumor development in “New melon” was most severe when the cultural soil was infested with approximately 107 CFU/ml of 0.05% (v/v) inoculum. In conclusion, “New melon”, which was able to show clear and severe symptoms in the root and hypocotyl, was judged to be the most suitable plant to perform the pathogenicity test of Streptomyces sp. The optimal inoculum density for disease development in the root was verified to be approximately 5×103 CFU/ml in cultural soil.
To validate the possibility of integrated pest management (IPM) utilizing natural enemies against spider mites (Acari: Tetranychidae) during the seedling-rearing period of strawberry, we investigated the dominant species of their natural enemies both on kidney bean traps infested with Tetranychus urticae Koch and on strawberry seedlings in four seedling-rearing fields per year in 2010 and 2011. While the predatory thrips, Scolothrips takahashii Priesner and phytoseiid mites were predominantly captured on the traps, predatory thrips was the only natural enemy observed on strawberry seedlings in all fields. Even when the densities of spider mites on strawberry seedlings were relatively low, predatory thrips were frequently observed. These results suggest that S. takahashii could be an effective agent to control spider mites in IPM for a seedling-rearing period of strawberry.
The ability of the predatory mite Amblyseius swirskii Athias-Henriot to feed on some species of crop fungi was investigated to determine the effect of plant fungi on mite development and reproduction. Larval and nymphal survival, developmental duration, total oviposition, and female longevity of the mite were compared among different dietary regimes: cucurbit powdery mildew on pumpkin leaf, Pinus thunbergii pollen, Ephestia kuehniella eggs, pumpkin leaf, mycelia of sooty mold, mycelia and conidia of sooty mold, Potato sucrose agar medium, and distilled water. Mites completed development and laid eggs only on cucurbit powdery mildew, P. thunbergii pollen, and E. kuehniella eggs. Mites fed mildew took 1.5 days longer to complete their development than those on the other two diets, and adults oviposited significantly fewer eggs than those fed E. kuehniella eggs, but similar numbers as those fed P. thunbergii pollen. These results demonstrated the possibility that the plant fungus cucurbit powdery mildew facilitates mite colonization and reproduction on crops.
We examined the effects of trichomes and the glandular trichome exudate on the survival of the predatory mite Amblyseius swirskii on young potted tomato plants. Removing the trichomes from the plant surface increased the survival rate from 0.8% (untreated plants) to 12.2% and decreased the mortality on plants from 63.3% ( untreated plants)to 0%. Almost all of the dead mites on untreated plants were observed adhering to the sticky secretions from trichome glands. To evaluate the toxicity of the secretions, we tested the effects of its main components (2-tridecanon and 2-undecanon) on A. swirskii by exposing mites to these chemicals for 48 h. All mites survived treatments with either of the chemical concentrations alone or a blend of these two chemicals. These results suggest that the main cause of the mortality of A. swirskii on tomatoes is not the toxicity of the secretions, but rather adhesion to the sticky secretions from the glandular trichomes.
Maize orange leafhopper Cicadulina bipunctata is distributed widely in tropical and subtropical regions of the Old World and feeds on various Poaceae. This species induces maize wallaby ear symptom, which is characterized by stunted growth and swelling of leaf veins. In Japan, damage by the leafhopper to young seedlings of the second forage maize crop was reported from Kumamoto Prefecture in the late 1980s. Because C. bipunctata is a potential pest of various cereal crops and the damage might become more severe due to global warming, we investigated the distribution of C. bipunctata in northern Kyushu and eastern parts of central Kyushu where an intensive survey has not yet been conducted. As a result, we newly collected the leafhopper from Oita Prefecture and clarified its wide distribution in eastern parts of central Kyushu. The leafhopper was not found in northern Kyushu including northern parts of Oita and Fukuoka Prefectures. This result indicates that the leafhopper is broadly distributed in lowland areas of central and southern Kyushu. Attention should be paid to a potential risk of damage by this leafhopper to various cereal crops in these areas.