In the winter of 1964,the author studied on the aquatic insect communities of the lower parts of seven rivers flowing into Lake Biwa, and calculated the biotic index based on the BECK-TSUDA method. The author wishes here to report the results and to compare them with the data of the investigation of the summer of 1963. The results are summarized as follows : 1. The temperature of the river water in winter (at the time of the sampling) does not exceed 11℃ in the lower part of the seven rivers, while that in summer (at the time of the sampling) exceeded 20℃. The pH value was 7.0〜8.3. 2. In the seven rivers, the fauna of the aquatic insects differed between in winter and in summer. 3. Three rivers (Yogo River, Hino River and Ishida River) had richer standing crop of aquatic insects in winter than in summer. But in four rivers (Ado River, Chinai River, Okawa River and Ane River), the standing crop was nearly equal in both seasons. 4. In the seven rivers, the rate of the standing crop of each life form differed between in winter and in summer. 5. In the three rivers (Yogo River, Okawa River and Hino River), a higher biotic index was obtained in winter than in summer for various reasons.
As a pioneer stage in the secondary succession the Ambrosia elatior community (Figs. 1,2) is widely distributed in the Kanto District extending up to 1400m above the sea level. The most common main course of the early succession is the Ambrosia→Erigeron→Miscanthus→Pinus→Machilus-, Shiia-stages. The vegetation and the buried-seed population in the soil at the Ambrosia stage in the campus of the Chiba University were studied (Figs. 3,4). The buried-seeds were separated from the soil and litter by the method of using the K_2CO_3 solution as in the previous paper (NUMATA et al. 1964). The floristic composition of the Ambrosia stage is shown in Table 1 where the density/m^2 of Ambrosia is 156 and it is stratified with three modes as the height varies (Fig. 5). Digitaria and Setaria are distributed randomly like Ambrosia, but they are low in height (10〜16cm) under the stratified structure organized by the dominant Ambrosia. The floristic composition of the buried-seed populations in June and December is shown in Table 2. It is noticeable that the composition and the quantities of species in each month are not similar and there is a definite relation satisfying the law of geometrical progression between the number of seed-grains and the rank of species (Fig. 6). Here we discuss the buried-seed population under the concepts of GSP and SSP. The total number of buried-seeds at a time is called the"gross buried-seed population"(GSP) and the total number of seeds produced in one growing season of a seral stage, for instance the Ambrosia stage, is the"seral seed production" (SSP). A phenomenal SSP of the Ambrosia stage is about 16,500/1m^2×1cm soil.
Growth variability, survival rate and aggressive behaviour of the individuals of small size variation of the normal, blinded and lens-removed juvenile rainbow trout in small experimental populations were studied during five weeks. 1) Aggressive behaviour disappeared by the removal of the eyeballs but it was retained after the removal of the lens only, although in this case territorial defence became unstable. 2) The survival rate and the coefficient of variation of body weight in the blinded group were remarkably greater than those of the other two groups at the end of the experiment. 3) Between the normal and lens removed groups there were small differences in the survival rate and coefficient of variation of body weight. 4) Some mechanism other than aggressive activity, e.g. difference in olfactory scense against food materials, might cause the increase in growth variability of the blinded fish.
The dispersal of three species of plant-and leafhoppers was studied in a rice plant nursery and in the paddy field, using the mark-recapture method, i.e. Delphacodes striatella, the small brown planthopper (S.B.P.) ; Nephotettix cincticeps, the green rice leafhopper (G.R.L.) ; and Deltocephalis dorsalis, the zigzag striped leafhopper (Z.S.L.). When the rate of recapture was high, the relation between log-transformed numbers of recapture and distance from point of release was expressed by a linear regression. Dispersal rates strongly decreased with time. In the nurseries, the maximum distances of recapture after one day were : -S.B.P., 10〜15m ; G.R.L., 7〜13m ; Z.S.L., 10〜13m. After five days the maximum distances were : -G.R.L., 15m ; Z.S.L., 28m. In the paddy fields, G.R.L. had covered the maximum distances of 23〜41m in the first day, and of 26〜35m in the second and third days. In the nurseries, the mean distance of dispersal per day were estimated at 7.5m for S.B.P. ; 6.3m for G.R.L. ; and 7.1m for Z.S.L. In the paddy fields, the mean distance of dispersal for G.R.L. were estimated at 12.5m per day, and 13.7m per two days in Station B ; and 16.6m per three days in Station C.
The observations on the seasonal abundance of insect pests attacking the young branches and leaves of citrus tree were carried out since the spring of 1962 at the citrus orchard of Omura City, Nagasaki Prefecture. Thirty-three Satsuma orange (Unshu Mikan) trees of six or seven years old were used for this study. In this orchard, the pesticides were not sprayed since the beginning of the study. The most injurious insect pests of the young branches observed in the orchard were composed of the undermentioned four species. (On the contrary, old branches were attacked by some species of scales, white flies and mites). Citrus leaf miner, Phyllocnistis citrella STAINTON (larvae) Citrus leaf roller, Agonopterix culcitella HERRICH-SCHAFFER (larvae) Citrus swallowtail, Papilio xuthus L. (larvae) Citrus aphid, Toxoptera citricidus (KIRKALDY) (nymphs and adults) All of the larvae of citrus leaf roller in the rolled leaves, larvae and pupae of citrus leaf miner in mines, eggs, larvae and pupae of citrus swallowtail and the nymphs, adult of citrus aphid were counted once a week. At the same time, the number of young leaves available for the food of these insects were counted. The maximum number (summation of 33 trees) of the citrus leaf miner is 3830 individuals, citrus leaf roller 586,larvae of citrus swallowtail 15,and the citrus aphid (nymphs) exceeded 15000. In this district, the citrus trees normally shoot three times a year. Sometimes, only one or two times of shooting takes place in a year according to the age or other conditions of the trees. The leaves are most abundant on the spring shoot. In 1962,two times of shooting viz. the spring shoot and the summer shoot were seen in the orchard. Citrus leaf roller and citrus swallowtail showed two peaks of population density. But, the citrus leaf miner and the citrus aphid were most abundant at the time of the summer shoot only (Fig. 3 and 5). In 1963,three times of shooting of citrus tree takes place in this orchard. Citrus leaf roller and citrus swallowtail showed three fluctuations in this year in the orchard. Citrus leaf miner and aphid were most abundant upon the summer and autumn shoot (Figs. 4 and 6). From the observations, it seems that the seasonal abundance of the population of the citrus leaf roller and citrus swallowtail synchronizing with the shooting (it means the seasonal abundance of available food of each species) of citrus trees. But the population size of the citrus leaf miner and the citrus aphid grow up as the summer and autumn shooting. The former two species has three (or sometimes four) generations in one year. The seasonal abundance (which are determined by the time of shooting) of them has the synchronization with the physiological rhythms of citrus trees. And the later two species has ten or more generations in a year. The seasonal abundance of these species may be determined by the time and amount of the summer and autumn shoot of the young leaves.
The results of pollen analysis of the Miocene lignite samples obtained from the Jurizuka oil field in the Shonai oil fields are reported. More than 29 genera of Fossil pollens were identified ; some of them are extinct in Japan. Pollen grains of broad leaved trees were found predominantly in the strats from 1668 to 1844m depth, while those of the needle leaved trees from 1924 to 2000m. The climate during the accumilation of the upper strata is thought to be more moderate than that of the lower.
Rhododendron tschonoskii is a deciduous shrub distributed in Japan and South Korea, occurring mostly on ridges or rocky slopes in the subarctic and the cool temperate zone. As the result of the phytosociological study of the Rhododendron tschonoskii community in Shikoku, it can be subdivided into the R.-Phyllodoce nipponica and the R.-Carex blepharicarpa community. The former is a heath-type community on the ridge near the Besshi copper mine. The latter occurs on high ridges in the Tsurugi and the Ishidzuchi mountain range, and its floristic composition is similar to that of the Sasa-Carex-type grassland. At present the phytosociological rank of this Rhododendron tschonoskii community, and other deciduous scrubs at high altitudes in Shikoku is still uncertain. This community, however, contrasts physiognomically with the grasslands and climax forests, and may be comparable to the Rhododendron kiusianum community on volcanoes in Kyushu.