[in Japanese]

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[in Japanese]

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Recently, tomato and eggplant baterial wilt caused by Pseudomonas solanacearum has caused serious damage in farmers fields. In this paper, physical, chemical, cultural, biological and integrated control were tested for tomato and eggplant bacterial wilt in heavily infested fields. In the control of tomato bacterial wilt, a susceptible variety, Toko-K and Momotaro showed 100% wilt with or without chloropicrin, but the moderately resistant variety Zuiei suppressed disease incidence under the same conditons. Wilt percent of Momotaro grafted with MATE, BF-Okitsu 101 or BFNT-R were 80%, 93.3% and 50%, respectively with chloropicrin treatment in 50 days after transplanting. Non-grafted plants had a very low percent (0-30%) of wilt. Especially, Kagemusha had excellent suppressivenss when grafted to Momotaro. Physical control with root-proof sheet, and chemical control with chloropicrin had good suppression in the early stage of crop growth, but the suppression did not continue to the late stage of plant growth. Treatment of charcoal compost fixed with Bacillus subtilis and Actinomycetes to the nursery soil and planting hole slightly decreased disease incidence. Treatment with the VA mycorrhizal fungi, Gigaspora margarita or Glomus sp. did not suppress disease incidence when applied alone, but when combined with charcoal compost the control was better. Integrated control combining physical (root-proof sheet), charcoal compost with antagonists, and chemical (chloropicrin) showed 10% wilt using the moderately resistant variety, Zuiei, but in the same conditions, the susceptible variety, Toko-K were 100% wilted. In the control of eggplant bacterial wilt, resistance of the varieties Kokuyo, Senryo-2, Tunonasu, Hiranasu, Torvum vigour and Tiwan-Naga were checked. The former 3 varieties showed 100% wilt, but the latter 2 varieties had no wilt. From these results, the strain of the pathogen of this field seemed to be race II . Kokuyo grafted with Meet and Karehen had 15% and 35% wilt respectively, but non-grafted plants did not wilt. Physical control (root-proof sheet) alone or chemical control (chloropicrin) alone were tested for eggplant bacterial wilt. Kokuyo when grafed with Meet had 90-100% with or without chloropicrin treatment. But when combined both treatments resulted in a decreased wilt percentage. The conclusions of these studies indicated it is necessary to develop integrated control fitted to the pathogen density in a particular field and more studies are needed on the infection mechanisms of these diseases.

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Rhizoctonia isolates from strawberry were characterized for oprimum temperature of mycelial growth, nucleus number and anastomosis group. Biological control of chinese cabbage bottom rot and strawberry bud rot caused by Rhizoctonia solani AG2-1 were also tested using antagonistic microorganisms from soil. One multinucleate isolate (Stw001) was identified as R. solani AG4 by anastomosis analysis and nuclei staining. Three others binucleate isolates (Stw002, 3, 4) were identified as Rhizoctonia spp. Optimum temperature of mycelial growth of Stw-001, 002, 003, 004 and Rf1-0 was between 28-30°C, and AG2-1 was 23°C. Stw001 and AG2-1 were pathogenic to chinese cabbage and strawberry. Sixty two microorganisms (167 isolates) inhibited mycelial growth of R. solani AG2-1 and AG4, and two isolates (Kr013 and Kr020) of 68 antagonistic microorganisms had a suppressive effect on disease development of chinese cabbage bottom rot and strawberry bud rot caused by R. solani AG2-1 or AG4 when applied as a seed treatment or as a planting hole treatment with a charcoal carrier.

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Recently there has been increasing concern about citrus scab resistance to Benzimidazole. An examination of sensitivity of Elsinoe fawcetti to Benzimidazole was conducted using Benzimidazole amended potato-dextrose agar. Only two of 42 test strains had growth inhibition at a concentration of more than 1 ppm and were therefore sensitive to Benzimidazole, while 40 strains had floral proliferation even at a concentration of 100-800 ppm, suggesting they had acquired high resistance.

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The application of the direct colony thin-layer chromatography for the identification of phytopathogenic bacteria was conducted. One-loopful bacterial colony was pasted directly to the origin on silica gel TLC plate and dried completely. This plate was developed at 25°C for 10 min until the solvent front will reach 6 cm line from the origin spots with chloroform-methanol (CM, 2:1, v/v) . After drying, bacterial cells were scraped out from the plate. Then, the plate was developed at the same direction with chloroform-methanol-1.25-5M ammonia (CMA, 60-80:25:4, v/v/v) or chloroform-methanol-water (CMW, 60:25:4, v/v/v) for ca. 1-1.5hr. After drying for more than 30 min, the spots were visualized by ninhydrin-spraying with successive heating at 100°C for 10 min. The chromatogram was recorded by a photograph or photocopy. Ideal chromatogram was obtained with chloroform-methanol-1.25M ammonia (60:25:4, v/v/v) or chloroform-methanol-water (60:25:4, v/v/v) as the second developing solvent-systems. Well reproducibility of chromatogram was observed when the conditions of TLC and culture age of the sample bacteria were kept steadfastly. Distinct differences among the chromatograms were observed at generic level. Especially, the difference between Clavibacter sp. (gram positive) and others (gram negative) was obvious. This method will be practically useful for a rapid identification of phytopathogenic bacteria.

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[in Japanese]

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Egg mortality factors of the whitebacked planthopper, Sogatella furcifera HORVATH were evaluated in paddy fields planted with a japonica variety, Hinohikari for 6 weeks from late-tillering to heading stage. The overall mortality rate was more than 80% throughout the census period with a peak of 92.7% at 7 weeks after transplanting. Physiological death caused by plant reaction against oviposition was responsible for 68.9-94.5% of the overall mortality. Mortality caused by this factor was highest at 7 weeks after transplanting and decreased as rice grew older. The parasitism rate by Anagrus sp. was estimated at 18.8-59.3% of eggs that escaped from the other mortality factors. The mortality rate due to predation and unknown factors was negligible except for the heading stage when it increased to 12.8%. Eggs laid in the central vein of leaves had a parasitism rate more than 3 times as high as those laid in leaf sheaths, while the physiological death rate was slightly higher in leaf sheaths than in leaves. The possible effect of each mortality factor on the population dynamics of S. furcifera was discussed with special reference to the role of physiological death.

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The efficiency of a fiberboard formulation (sex pheromone complex) impregnated with synthetic sex pheromone and insecticide (MEP) was tested in a field experiment to prevent damage by sweetpopato weevil, Cylas formicarius (FABRICIUS) in Amami-ohshima Is., Kagoshima, Japan in 1992. In an experimental plot sex pheromone complexes were applied twice at 0 and 45 days after planting with an additional insecticide (carbosulfan) application at 45 day after palnting of sweet potatoes. In the other plot insecticides (carbosulfan) were applied three times on 45, 65, 85 days after planting. The application of sex pheromone complexes plus insecticide was more effective in reducing damages to sweet potatoes by Cs formicarius than those of insecticides only. The numbers of Cs formicarius males captured in the sex pheromone traps in the experimental fields were not always consistent with the damages to sweet potatoes, suggesting that sex pheromone complexes might attract males from both inside and outside of the experimental field.

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[in Japanese]

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The characteristics of oviposition punctures caused by sterile females of the melon fly, Bactrocera cucurbitae, and an evaluation of its economic damage were investigated in Okinawa, Japan. It was confirmed in a field-cage experiment that sterile females make oviposition punctures (sterile stings) on cucurbit fruits. The features of sterile stings were different depending on the species of fruits and were classified into five types. The punctures on cucurbit fruits collected in fields were checked and identified as sterile stings or not, using the criterion obtained from the field-cage experiment. The rates of damaged fruits by sterile females were estimated to be lower than 1% in cucumber, sponge gourd and bitter gourd.

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A comparison between Encarsia formosa GAHAN and Encarsia transvena (TIMBERLAKE), the parasitoids of the tobacco whitefly Bemisia tabaci (GENNADIUS), was made by conducting laboratory experiments on host instar choice and functional response to host density. E. formosa preferred young instar B. tabaci larvae such as the second instar ones and old instar larvae such as the fourth instar for host feeding. E. transvena preferred fourth instars both for host feeding and oviposition. When fourth instars were used, the functional response of the parasitoids followed a saturation type curve in which E. formosa was superior to E. transvena both in host feeding and oviposition.

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Cabbage leaves were rooted by placing their petiole in water. Diamondback moth larvae were reared on them at constant temperatures of 10, 15, 20, 25, and 30°C. Pupae reared on rooted leaves were heavier than those reared on leaves having no roots. Pupae reared on rooted leaves were almost as heavy as those collected from cabbage fields. Rooted cabbage leaves were an excellent food for diamondback moth larvae, as the leaves remained in good condition as a food for more than 2 months.

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In order to determine the origin of the parasitoid, Torymus (Syntomaspis) sinensis native to Tsushima Islands, parasitoids of the chestnut gall wasp were investigated at several localities in South Korea, from where the parasitoid might have come flying accidently into Tsushima. As a result, the parasitoid was proved to occur throughout South Korea including Cheju Island. It was, however, concluded that the parasitoid populations of Tsushima and Korea were different from a Chinese population in the seasonal prevalence of adult emergence, and that the Tsushima population belonged to the same ecotype as that of the southern part of South Korea. Therefore, the Tsushima population either originated in southern Korea or was native to Tsushima where it originally occurred as a parasitoid of an unknown native cynipid host on a oak tree.

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Oviposition behaviour of two parasitoids, Torymus (Syntomaspis) sinensis and T. (S.) beneficus, was investigated on twigs with galls formed by the chestnut gall wasp, Drvocosmus kuriphilus. Oviposition behaviour of both parasitoids was composed of walking and flight, rest and preening, searching, host-feeding, and stinging. The sting behavior was separated into long and short time stings. The long time stings may correspond to paralysing the host larva, oviposition and construction of a feeding-tube. Frequency of long time stings of T. (S.) sinesis and T. (S.) beneficus are 4. 5 and 2. 3 per hour respectively.

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[in Japanese]

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The immigration of the Hawaiian beet webworm moth, Hymenia recurvalis, in a vegetable field at Nobeoka, Kyushu, was investigated in 1992. The moths on two host plants, Spinacia oleracea and Amaranthus lividus, were collected every day with a sweep net from 19 May. Collected female moths were dissected to determine the number of matings and the maturity of their ovaries. The daily number of moths cuptured was one or zero for ten days prior to 6 June, but the total number of moths suddenly increased to 64 during 8-10 June. Every female moth collected before 6 June had mated and had matured eggs. However, the female moths collected in the above three days included 85, 94 and 88% mated moths and 67, 89 and 88% matured moths suggesting the arrival of fresh moths. Two rice leaf roller moths, Cnaphalocrocic medinalis, a migrant moth, were also collected. Synoptic charts indicated that a depression occurred in central China on 5 June and the front that accompanied the depression moved to the East China Sea and then moved eastward across Kyushu on 7 June. The movement of the front appears to have brought the increase of the moth.

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