[in Japanese]

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[in Japanese]

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Melon yellow spot virus (MYSV) is a new tospovirus which is spreading quickly in Kochi Prefecture, Japan. A PCR-microplate hybridization (PCR-MPH) method for the detection of MYSV from plants (cucumber) and thrips was developed. A primer set (NF3, 5'-TTAAACTTCAATGGACTTAGAYCTGG-3': NR3, 5'-TTAAACTTCAATGGACTTAGAYCTG-3') was designed based on degenerate sequences of the nucleocapsid protein gene on the S RNA of MYSV. A DNA fragment of approximately 900 by was amplified from MYSV-infected plant tissues and labeled with digoxigenin (DIG). The sensitivity of PCR-MPH was compared with those of ELISA and RT-PCR. The total RNA was purified from 0.02 g of MYSV-infected plant tissue, and diluted in 5-fold steps from 5¹ to 5¹⁰. MYSV was detectable from a 5¹⁰-fold dilution by PCR-MPH, which is 625 times more sensitive than ELISA or RT-PCR. Moreover, MYSV was also detected from individual thrips by PCR-MPH with a higher sensitivity than RT-PCR.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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Three different incompatible isolates (showing severe, moderate and weak pathogenicity to loquat twigs) of A group of Pseudomonas syringae pv. eriobotryae, the causal bacterium of loquat canker, showed a change of virulence by repetated inoculation to loquat leaves 62, 71 and 117 times, respectively. A negative correlation was detected between the severity of disease on twigs caused by the incompatible isolates and the number of repetated inoculations for acquisition of pathogenicity. The three variant isolates formed similar neclotic lesions without haloes on the leaves. Necrotic and halo lesions were formed on the leaves by mixed inoculation with a bacterial suspension of the variant and the original isolate. No difference in the pathogenicities of the variant isolates to shoots and buds was found in comparision with those of the original isolates 6 months after acquisition of pathogenicity. The phage reaction and bacterial properties of the variant isolates were not different from those of the original isolate.

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The relationship between the occurrence of pecky rice induced by rice bugs and meteorological conditions was analyzed on the basis of rice grain quality data obtained in Kumamoto Prefecture in 1989-2001. The percentage of rice grains graded in the second category or lower because of the inclusion of pecky rice was positively correlated with the effective cumulative temperature above 12 t in March-September and the mean temperature in August and September, whereas it was negatively correlated with the precipitation and number of rainy days in August. These results suggest that pecky rice becomes a serious problem under weather conditions that facilitate population growth, feeding, and immigration of rice bugs into paddy fields.

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[in Japanese]

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[in Japanese]

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We investigated the occurrence of Spodoptera litura and three major stink bugs, Riptortus clavatus, Piezodorus hybneri and Megacopta punctatissimum, on three soybean cultivars/line-Kyukei 279 (line resistant to S. litura selected through laboratory tests), Fukuyutaka (standard cultivar) and Himeshirazu (resistant to S. litura)-in a field in Kumamoto, Western Japan, in 2001. The density of S. litura larvae was significantly lower on Kyukei 279 and Himeshirazu than on Fukuyutaka. The number of leaves damaged by colonies of newly hatched larvae was also lower on Kyukei 279 than on Fukuyutaka, suggesting that fewer egg masses were laid on Kyukei 279, and thus that S. litura females had less oviposition preference for Kyukei 279 than for Fukuyutaka. These results indicate that Kyukei 279 shows intermediate resistance to S. litura under field conditions. The larval and adult densities of the three stink bug species and the rates of bean damage by the bugs did not differ among the three cultivars/line. This suggests that none of the cultivars/line have resistance to the stink bugs. However, Kyukei 279 and Himeshirazu may have the tolerance with a higher compensation capability for stink bug attack than Fukuyutaka, since they are characterized by many pods with small beans.

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Traps containing the synthetic aggregation pheromone of the brown-winged green bug, Plautia crossota stali, were placed in conifer forests, which are its major reproductive site, and in a citrus orchard, where it does not reproduce, to investigate the pheromone's attractiveness to its parasitic fly, Gymnosoma rotundata, and its parasitic wasp, Trissolcus plautiae, in 2000 and 2001. For G. rotundata, traps in the forests captured greater numbers of the fly than traps in the orchard from May to July, whereas for T plautiae, traps in the orchard captured greater numbers of the wasp than traps in the forests from August to October. This suggests that the attractive traits of the P c. stali pheromone traps differ between the two parasitoids.

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Seasonal fluctuations in population density of Tetranychus kanzawai Kishida and predacious natural enemies were investigated in mulberry fields in 2001. T.kanzawai occurred in mid-April, and the population density had two peaks in early June and late August. Predacious natural enemies occurred later than the occurrence of T.kanzawai, and the dominant species varied among sampling dates. The occurrence periods and the timing of the peak population density of Oligota kashmirica benefica Naomi, Feltiella sp., Scolothrips takahashii Priesner. and Amblyseius womersleyi Schicha coincided with those of T kanzawai. It was suggested that the seasonal changes in population density of these four natural enemies were influenced by those of T kanzawai. Furthermore, the spatial distributions of Oligota kashmirica benefices, Feltiella sp. and Scolothrips takahashii larvae were positively correlated with those of T kazawai. On the other hand, the population density of A. eharai Amitai et Swirski did not coincide with that of T kanzawai. It is suggested that the prey of A. eharai does not necessarily depend on T kanzawai in mulberry fields.

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