Under experimentally controlled condition, population of the azuki bean weevil, Callosobruchus chinensis was subjected to be attacked by the parasite, Neocatolaccus mamezophagus. It is the main point of the present work to verify experimentally whether or not the balance of interacting system of host and its parasite exists when the density independent immigration, such as artificial adding of constant percentage, has an influence upon the host-parasite interacting system. The interacting population was maintained in the laboratory at 30℃ and 75% R.H. being supplied with constant amount of azuki beans as food in each generation. And a fixed number of both host and parasite population or host population or parasite population which is a certain percentage of control population was added to the original population of host-parasite system in every generation, and it was observed how the steady state was altered by these treatments. The methods of adding are as follows : Host was added during the first 6 days of host emergence. Host is full-grown larva on the 14th day after host oviposition, and parasite can easily lay its eggs in the host from outside the bean. Parasite was added for 4 days from 12th day after host oviposition. In all experiments, percentages of such adding of host or parasite population as mentioned above were 25,50,75 per cent of the control population. In any case of the adding, host-parasite system maintains a steady level of population density, but the steady state of each adding population changes its level from that of the non-adding population(as is shown in Table 2). When parasites were introduced into the population, the steady state moved to another density. This displacement of the steady density may be varied by the action of parasite. Neocatolaccus is a parasite attacking the full-grown larvae of the hosts and is unable to have an influence directly on the host population. The density of parasite population depends on the initial density of host, which has a considerable relation with the final density of host in the previous generation, and the density of parasite population has also the effect on the final density of host in a generation. After these consideration as to the determination of steady state in the host-parasite interacting system, it seems that the density effect of host population plays an important role.
1. Yatsushiro Plain consists of two parts : the alluvial land and reclaimed land from the sea. Both the alfuvial land and the reclaimed land are cultivated for rice in summer and for rush successively in winter. 2. The writer selected three stations in the reclaimed land and four stations in the alluvial land and investigated both the properties of water and the occurrence of algae at each station. 3. Rice-fields in summer and rush-fields in winter are much the same in the water properties. The occurrence of the microscopic algae excepting desmids is almost uniform throughout this area in summer, while the most of them disappear except diatoms in winter. The communities of Nitzschia kuetzingiana HILSE and N. palea (KUETZ.) W. SMITH are always dominant. Desmids are rather scanty in the reclaimed land owing to their intolerance to the richness of calcium. Cosmarian species and the dominant species of Nitzschia encountered in the rice-and rush-fields belong to a smaller sizes type. This is surely caused by the abundant organic substances in the water. 4. Occurrence of macroscopic algae is thought to depend upon the water temperature. In summer are proliferous Hydrodictyon reticulatum (L.) LAGERHRIM, Spirogyra setiformis (ROTH) KUETZING and Anabaena oscillarioides BORY distributing throughout the area, while in winter they are replaced by Tetraspora gelatinosa (VAUCHER) DESVAUX, Draparnaldia sp., Sphaeroplea annulina (ROTH) AG. and some species of Zygnema and Spirogyra being restricted within the alluvial land. Remarkable water-blooms of Euglena sp. accompanied by Pandorina morum BORY or Eudorina elegans EHR. and Nitzschia are proliferous all the year round without being influenced by water temperature. 5. The formation of water-bloom owes to long duration of fine weather especially in winter, and the communities of algae disappear when they are cut off from the full sun-light by the growth of the cultivated plants. The succession from the water-bloom of microscopic algae to macroscopic communities of dominant members proceeds quickly in summer due to the higher water temperature in rice-fields, but it goes on slowly in rush-fields because of the lower water temperature especially in winter.
Two kinds of experiment were carried out under controlled conditions of laboratory. In the first experiment, the copulation frequency in the population of newly emerged adult was observed for 30 minutes in different population densities ranging from one to ten pairs in the glass dish of 100cm^2 bottom area. After that, the fecundity (vis. the average number of eggs laid per female, eggs hatched, and emerged adults in the next generation) was examined. The copulation frequency increased exponentially with the increase of density, and this may suggest that the mating of this weevil is pursued largely by chance. The fecundity just increased proportionally with the copulation frequency. When the density is extremely low, it takes each male in a given population a very long time to encounter and mate with a female after the emergence. In this respects, it was investigated in the second experiment the effect of the duration before cohabitation from zero (within 24 hours of emergence) to six days on the fecundity. As a result, the fecundity decreased rapidly with the prolongation of that duration, and this sharp decline may prove that the weevil does not have any adaptability for such condition.
Along the lake side of Tofutsu in the vicinity of Abashiri City, the preaestival aspect of the forest of Alnus japonica var. arguta is characterized by the presence of Fritillaria camtschatcensis on which the present study was carried out in June 1962. 1. A distribution pattern of the flower-bearing individuals of Fritillaria camischatcensis was determined according to HOPKINS (1954). The area studied was (25×25) m^2 and the number per 1m^2 was 194.8. The Index(A)of HOPKINS was 1.862(p≪0.001)and the distribution pattern was to be inclined to the aggregative distribution. 2. Individuals of Fritillaria camtschatcensis were conveniently grouped into the three groups on the basis of the developmental stage : A)group-with only a leaf without a stem ; B)group-with stem having no flowers and flower buds. ; C)with stem having flowers and flower buds. On each type the stem height, the node number, the bulb size and the weight were measured. Generally speaking, the characters showed quantitatively to be A<B<C. 3. In comparison of leaf length, leaf width and average number of verticillate leaves per individual of F. camtschatcensis under investigation with those of the diploid and the triploid F. camtschatcensis investigated cytologically by MATSUURA(1935), it is suggested that the individuals of F. camtschatcensis under investigation will be the triploid which are commonly grown in the lowlands in Hokkaido.
Microbial metabolism occurring in the polluted river-water under anaerobic condition was analyzed from the standpoints of both anaerobic decomposition and self-purification. The result of surveys carried out on the River Sumida, Tokyo, revealed that sulfide formation was prominent especially during warmer season. In order to ellucidate the mechanism of this phenomenon, the river-water of the Sumida was brought into the laboratory experiments. When the river-water was incubated anaerobically at 35℃, vivid production of sulfide and decrease of sulfate were observed with the production of lower fatty acids. Of these acids, acetic acid was most abundant, and smaller amounts of butyric, propionic and formic acids were also recognized. From this medium, colonies of sulfate-reduction bacteria could be obtained by the use of solid lactate medium. To get more detailed information concerning the relation between sulfate reduction and organic acid metabolism, the microflora of the river-water was inoculated to the various synthetic media containing a single source of organic carbon. There was a significant reduction of sulfate in the presence of lactate, pyruvate, glucose, sucrose and starch but not in the presence of formate, acetate and propionate. Ethanol was slightly positive. Whenever any substrate was utilized as the hydrogen donor for sulfate reduction, acetate was produced most abundantiy as the stable end-product. In the light of the above-mentioned and other various data, it was assumed that carbohyrates discharged into the river-water underwent successive metabolism of lactic acid fermentation and sulfate reduction coupled with the formation of acetate from lactate.
A local outbreak of the grasshopper Mecostethus magister occurred in 1961 on a marshy grassland, 5 ha in area. This species completes its life-cycle in Miscanthus sinensis-community, excepting at the time of the outbreak when many individuals invaded into cultivated land. The population dynamics of this species from 1961 to 1963 was described briefly in the present paper. Number of adults emerged in this grassland was(25〜50)×10^4 in 1961,and 3.5×10^4 in 1962. A key-factor for this decrease was suggested to be flooding. As the grassland was submerged during July of 1961,most of females died having no time to oviposit their egg-pods. About 10 to 20 per cent of eggs were killed by predation, while no egg-parasite has been discovered so far. Nymphal mortality was high from the first to third instar but reduced after the fourth instar. The number of egg-pods laid in 1962 was remarkably larger than that in 1961,because of no flooding and low adult mortality. Soil profile showed that this grassland was gradually drying up due to artificial drainage of surrounding basin, offering good conditions for the grasshopper's propagation.