ITO, Yosiaki, Kazuyoshi MIYASHITA and Katsui SEKIGUCHI (Div. Ent. Nat. Inst. Agri. Sci., Tokyo and Chiba Pref. Agri. Exp. Sta., Chiba) Studies on the predators of the rice crop insect pests, using the insecticidal check method. Jap. J. Ecol. 12,1-11 (1962). To elucidate roles of polyphagous predators, especially of spiders, in natural control of insect pests of the paddy field, experiments with the insecticidal check method were conducted at two localities near Tokyo. In all the insecticide-treated plots, the green rice leafhopper and the planthoppers remarkably increased several weeks after the treatment. The rates of increase in the treated plots were higher than in the untreated ones. The primary cause of this increase was estimated to be the destruction of the spider populations by the insecticidal spray. Mortality of the rice stem borer larvae during their dispersal was lower in the treated plot than in the untreated one, suggesting an important role of the predation by the spiders and by other arthropod predators on the dispersing larvae. Life tables for the rice stem borer showed three mortality peaks, of which two were suggested to be mainly due to the predation. Within low density levels of the prey, the action of the spiders was dependent with the prey density, while it was density-independent or inversely density-dependent at high prey densities. This indicates a characteristic role of the polyphagous predators on insect populations. A schematic food-chain around the rice plant was presented according to the results of the present study.
KOYAMA, Juro (Univ. Tohoku, Sendai) The swarming behavior of Fannia scalaris FABRICIUS with special reference to the swarming individual number. Jap. J. Ecol. 12,11-16 (1962). Observations and experiments were made on the swarming behavior of Fannia scalaris FABR. under the willow street tree in Sendai from July to August in 1957. The adults of Fannia scalaris FABR., most of which are males, fly about in a swarms under the crown of the willow street tree. Mating is often observed among the swarming flies. It is characteristic that swarming males frequently pursue each other. Besides, many males and females rest and feed on the leaves and branches of the tree. The diurnal rhythm in the number of swarming individuals is bimodal, that is, numerous in the morning and also in the evening when they expand their swarming range. It seems that the present daily rhythm depends upon the environmental conditions, especially the light condition. It is noticeable from the viewpoint of the population ecology that coaction among the swarming flies seems to relate closely to the limitation of the swarming individual number. Experiments were made to ascertain the above assumption, and the results obtained were : (1) Fluctuations of the swarming individual numbers at two adjoining trees were parallel to each other. (2) When the swarming flies under the crown of a tree were artificially removed, they become replaced by the flies which came from leaves or branches of the same tree. From the above, it is suggested that the swarming individual number is limited by a certain mechanism, seemingly related with the interaction among swarming flies. It is considered that the mechanism mentioned above is common at least to the adjoining trees.
ITO Koji and Teruo LBU (Univ. Hokkaido, Sapporo) The salt marsh communities in the northern part of Lake Notoro near Abashiri in the north-eastern part of Hokkaido, Japan.-Ecological studies on the salt marsh vegetation in Hokkaido, Japan (5)-Jap. J. Ecol. 12,17-20 (1962) Synecological studies on the salt marsh communities were carried out in the Summers of 1960 and 1961. The communities studied were classified into : Salicornia europaea association (Salicornia europaea sociation), Puccinellia kurilensis-Glaux maritima var. obtusifolia ass. (Puccinellia kurilensis isocion, Puccinellia kurilensis-Glaux maritima var. obtusifolia soc., Glaux maritima var. obtusifolia isocion), and Potentilla Egedei var. groenlandica society. Among of them the Glaux isocion has not been reported in Japan. The isocion in the present area occupied about 3 ha., being nearly the half of the whole area investigated. Comparing the present isocion with the Glaux maritima DAHLBECK isocion in England, it is suggested that our isocion developed in a wetter habitat. The soil salinity of rhizospheres were measured at 20 points, and the salinity ranges of the dominant plants were : Salicornia sp. ; 5.7〜33.6‰, Puccinellia sp. ; 5.4〜14.5‰, Glaux sp. ; 1.2〜14.5‰ and Potentilla sp. ; 1.2〜4.5‰.
TAKAHASHI, Hisataka (Komatsushima Gymnasium, Tokushima) Saisonachwankung der Schwarmformation der Stechmucken (Culex pipiens pallens COQUILLETT) in der Abenddammetung. Jap. J. Ecol. 12,21-26 (1962). In dieser Unterauchung wurde im Verlauf von zwei Jahren der Anfang der Schwarmfor mation der Stechmucken (Culex pipiens pallens COQUILLETT) in der Abenddammerung an einem bestimmten Platz im Zimmer fortwahrend beobachtet und dabei der Zusammenhang mit Beleuchtungsstarke, Temperatur, Feuchtigkeit, Zeitpunkt und Wetter betrachtet. 1) Die Beleuchtungsstarke, worin die Schwarmformation anfangt, bezieht sich auf die Temperatur und verandert sich zufolge der Saison. D.h. sie ist im August niedrig, wird allmablich davor und-nach hoch und steigt rasch ungefahr um November. 2) Die Beleuchtungsstarke, worin die Schwarmformation anfangt, stimmt je nach der Stelle der Beobachtung, wie im Zimmer, im Freien u.s.w. nicht in ihrer Hobe liberein. 3) Die Beleuchtungsstarke am Anfang der Schwarmformation ist niedrig, obgleich die Temperatur bei regnerischem Wetter niedriger als die bei wolkigem und klarem Wetter iat. Und die Beleuchtungsstarke am Anfang der Schwarmformation um September und Oktoberist niedriger als die um Mai und Juni, obgleich die Temperatur in beiden Salsons ungefahr gleich ist. 4) Die Beleuchtungsstarke am Anfang der Schwarmformation ist konstant bei der hoheren Temperatur, aber sie ist unbestandig bei der niedrigeren Temperatur. 5) Der Zeitpunkt des Anfangs der Schwarmformation ist bei regneriachem Wetter am fruhesten und bei klarem Wetter am spatesten. 6) Die Zeitdifferenz zwischen dem Zeitpunkt des Anfangs des Schwarmformation und dem des Sonnenuntergangs verandert sich nach der Saison. 7) Die Tatsache ist zu bedenken, dass auch die Feuchtigkeit auf den Anfang der Schwarmformation einwirkt.
YOSHIOKA, Kuniji and Takao KANEKO (Univ. Tohoku, Sendai) The distribution of plant communities due to topography in a part of Mt. Hakkoda. Jap. J. Ecol. 12,26-31 (1962). The distribution of plant communities was studied in an area ranging from 800 to 1,360m in altitude on Mt. Hakkoda, Aomori Prefecture, Northeast Japan. The lower part below 940m in altitude is occupied by the montane zone of Fagus crenata and the upper one by the subalpine zone of Abies Mariesii which covers the greater part of the area studied. The forest of Abies Mariesii is a representative of the subalpine zone, although it does not cover the whole zone. The forest of Abies Mariesii occupies places from moderate to steep inclination and is distributed from the north through the west to the south. It is replaced in the east by the deciduous broad leaf scrub, the Sasa kurilensis and the snow patch communities, and on a flat by the Sphagnum moor. These differences in distribution are caused by the topography which has a great effect on the depth of snow-cover and the drainage of the habitats.