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In 2003, mosaic or witches' broom symptoms were observed in water dropwort plants in Akita prefecture, Japan. At first the causal agent of the plants with the mosaic symptoms was thought to be Celery mosaic virus (CeMV) on the basis of the descriptions of typical symptoms. However, RT-PCR and sequence analyses of the coat protein gene indicated that the plants were not infected with CeMV, but with Japanese hornwort mosaic virus (JHMV). In the plants showing witches' broom, a typical symptom of phytoplasma infection, infection with a phytoplasma was con firmed by PCR analysis. This is the first report on the occurrence of JHMV and phytoplasma in Akita prefecture. By using RT-PCR and PCR analyses, six healthy plants were selected as pathogen-free stocks.

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A primer set (virD2-03 primer and virD2-06 primer) for PCR analysis was designed for the detection of Agrobacterium vitis isolates from grapevine in Hokkaido, on the basis of the sequences of the virD2 gene located on Ti and Ri plasmids. With the virD2-03 primer (sequence: 5'-GCCGAGATGTTTGGGTCAGG-3') and the virD2-06 primer (sequence: 5'-TGGCGCCGAGATATCTTCAGCCA-3'), a 146 bp fragment was ampli-fied from cell lysates in 41 A. vitis isolates from Hokkaido, whereas no PCR products were obtained from the Agrobacterium radiobacter isolates tested. Thus, the primer set designed in this study is useful for the detection of A. vitis isolates from Hokkaido.

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The seasonal prevalence of the seed corn maggot Delia platura was studied in the central part of Hokkaido, of the northern Japan, in 2003-2005. The flies captured by a malaise trap set in winter wheat or sugar beet fields were examined. For the female flies, ovaries were classified into the following three stages: without any visible eggs, with immature eggs, and with mature eggs. The results showed that D. platura goes through five generations a year in central Hokkaido. The second and third generations may become indistinct owing to their small numbers of flies caused by temperatures (>20°C) unsuitable for development and survival. We suggest that the developmental zero and the effective cumulative temperatures are useful for forecasting the occurrence of each generation of the fly.

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We surveyed flower-visiting insect fauna on canola in Morioka City (39.7°N, 141. 2°E) for three years (2003-2005), and found that more than 75 species (6 orders; 40 families) have some assocation with canola flowers. Among them, the honeybee (Apis mellifera) was predominant species and seems to be the most important species in terms of gene flow among canola cultivars. In 2004, a large numbers of honeybees foraged on the experiment field in only a few days, and no such event was observed in other fields on the same days, or in the same fields on other days during the three-year observation. This event suggests that the artificial movement of the pollinators should be considered in the evaluation of the gene flow of the genetically modified (GM) plants.

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Two strains of the diamondback moth Plutella xylostella were selected for fast or slow developmental speed. The egg-larval period in the 7th generation of the fast-development strain (PxTF) was 16.0 days, which was 0.9 days shorter than that before selection (16.9 days), and that of the slow development strain (PxTS) was 20.5 days, which was 3.6 days longer than that before selection. The female forewing length in the 10th generation of PxTF was longer than that in the 8th generation of PxTS. The pupation rate in the 8th generation of PxTS was only 65.9%, whereas in the 10th generation of the PxTF it was 95.2%.

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The optimum number of repetitions of the petunia leaf disk assay for detecting a Frankliniella occidentalis adult that transmits Tomato spotted wilt virus (TSWV), was determined. Of thrips adults that transmitted TSWV once or more when three successive assays were performed, 87.7% of the females and 90.9% of the males trans-mitted the virus in the first assay. Thrips that transmitted the virus in the second and third assay for the first time comprised 10.5% and 1.7% of the females and 6.8% and 2.3% of the males, respectively. In conclusion, it is necessary to repeat the assay twice to detect a thrips transmitter of TSWV accurately.

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The distribution of the pea leafminer Liriomyza huidobrensis expanded in Aomori prefecture. Nine new host plants species were found in 2005, and as a result, a total of 37 species of plant across 18 families were recorded as host plants in Aomori prefecture. The effects of granular insecticides against L. huidobrensis on kidney bean leaves were examined in the laboratory. Five insecticides, clothianidin, dinotefuran, thiamethoxiam, acetamiprid and nitenpyram, were tested. None of the insecticides was highly toxic on larvae and suppressed the number of oviposition punctures. The application of nitenpyram decreased number of feeding punctures and was highly toxic to eggs. It is considered that nitenpyram is a practical insecticide when it was applied to the soil just after planting ornamentals and vegetables.

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The role of tabanid flies as pollinators of buckwheat was investigated in Horokanai, Hokkaido in July and August, 2002. One hundred and sixty-four flies belonging to five genera and nine species were captured by a trap in a meadow 300 m from the nearest buckwheat field and isolated by a grove, and 77 flies of four genera and eight species were captured by a trap beside the buckwheat field. Almost all the flies captured in this investigation had pollens attached to their bodies including buckwheat pollen. More than half (56.7%) of the flies captured even those from the meadow were determined to have attached buckwheat pollen to their bodies. Thus, it can be concluded that tabanid flies play a role in the pollination of buckwheat.

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