Domestic pigeons produced viremia almost readily for first 5 days when they were inoculated with Japanese encephalitis (JE) virus. JE virus persisted in liver and kidney of one pigeon out of 6 used at least for 39 days. Immune response of infected pigeons was not high, and the antibody levels decreased gradually through a 15-week observation. No cyclic fluctuation of antibody levels was observed during the observation period. The mosquito Culex tritaeniorhynchus was infected by feeding on a viremic pigeon when the virus concentration of blood exceeded (10)^<1.3> suckling mice (ICLD)_<50>/0.02ml. The tick Argas japonicus, on the contrary, failed to accept the virus through the feeding on the viremic pigeon. These findings had different pictures from those of West Nile virus infected in pigeons and Argas ticks.

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[in Japanese]

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Field tests of rat control were carried out in residental areas to know a pattern in consumption of baits with warfarin and thallium sulfate and also to know the estimating method of the rat population exposed to the baits by daily consumption of them. The dominant species inhabiting in these areas were Rattus norvegicus and Rattus rattus. It was observed that about one third of the exposed population of the rats in the experimental area fed warfarin baits on the first day, about two third on the second day and the maximum consumption was shown on the third day. Thereafter, feeding rate decreased. It was thought that three day intake of 0.03% warfarin bait was enough to kill almost all of the rats. If the population is very large of infiltration in rat from outside into the experimental area might be expected, the pattern of the bait consumption should be complicated. When rats were exposed to thallium sulfate baits, 33-44% of the total population would take the baits every day. In this case, one intake of the baits is fatal to rats. In both cases, rat population exposed to the baits could be estimated by the same method as the removal method by traps.

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A series of studies have been carried out by us on the horse fly, Tabanus iyoensis Shiraki, which is a serious pest in certain areas in Toyama Prefecture. The present study mainly deals with the results of field and laboratory observations in its life history, with emphasis on the possibility of its autogenous reproduction. The results of dissection of females caught with both dry-ice traps and with insect nets have revealed that their parous rates are surprisingly high (93%, 543/584) even in the early season of their appearance (late July to early August). It is presumed from these observations that the horse fly mostly deposites autogenous eggs before taking the first blood meal. It has been also confirmed that the female horse flies reared from pupae in the laboratory mostly deposit eggs before taking a blood meal, even when the blood source is available. However, the blood meal seemed to be necessary for producing the second and the subsequent batches of eggs. The appearance of surprisingly large numbers of this horse fly seems to be due mainly to the involvement of such autogenous reproduction, especially in areas where almost no blood sources are available. Such an unusual mode of reproduction as the horse fly seems to be sufficient for maintaining their population density in large areas, and makes its control to be difficult.

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The seasonal fluctuation of the density of larvae and pupae of Culex tritaeniorhynchus in paddy fields was investigated at Sijyonawate-cho, 1968-9. The number of larvae and pupae varied seasonally at each paddy field. In some paddy fields, the number of larvae and pupae tended to be maintained at relatively high level. On the contrary, in some paddy fields, for example, in paddy field L, the number of larvae and pupae was always smaller than the average. The number of 1st and 2nd instar larvae tended to be larger in the paddy fields in which the density of larvae was always high than in the ones in which the density was low (Fig.1). Water samples were taken from the paddy fields to check the survival rate of the 1st instar larvae in the laboratory at 30℃, 16 hr. illumination. The survival rate was higher in the water from the paddy fields where larvae were abundant (Fig.1, 2, Table 1). Higher survival rate was observed in the water taken from the paddy field at certain season when the number of larvae was high (Fig.3). However, when 0.1g of artificial food per pot was added to the water from paddy fields in which the density of larvae was low, the survival rate increased (Fig.2, Table 2). This suggests that the low value in the survival rate in water from some paddy fields may be attributed to the deficiency of food.

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The epidemiological and entomological studies in the past have revealed that Japanese encephalitis in Japan usually spreads among pigs in early summer season and is transmitted to man mainly by the mosquito Culex tritaeniorhynchus. The number of clinical encephalitis cases that occur in certain area is therefore considered to be determined roughly by the following formula : X=A×B×C×D×E×H^f×1/(-log_e H)×1/G×I×J×K, where X : the number of clinical cases in certain area in one season; A : the total number of pigs in this area; B : the percentage of pigs that produces viraemia in one season; C : the average length in days of the viraemia sufficient to infect the mosquitoes; D : the average number of the mosquitoes that feed on the pigs per day per pig during the viraemia season; E : the percentage of mosquitoes susceptible for the development of the virus; F : the average length of days required by the mosquitoes to become infective; G : the gonotrophic cycle in days of the mosquitoes; H : daily survival rate of the mosquitoes; I : the percentage of mosquitoes that feed on man in one bite; J : the percentage of people in the area who are susceptible (non-immune) to the virus; K : the percentage of people among the susceptible population who develop clinical symptoms after infected with the virus. The above formula can be applied when the mosquito density per man is relatively low and the people is not bitten by more than one infected mosquitoes. When the infective rate (S) and the average number of mosquitoes that bite man during the infective season (U) is known, the probability of a man receiving one or more infective bites (V) is obtained by the formula : V=1-(1-S)^U The infective rate (S) and the average number of mosquito bites per man (U) can be estimated directly, or by mathematical assumption from observed data. Therefore, the number of cases (X) can be estimated by the following formula, if the mosquitoes attack the people almost evenly : X=P×J×K×V, where P is the size of population of this area. The frequency distribution of the numbers of mosquito bites per man is, however, probably not "normal", but is considered to be more or less skew. If it is highly skew, such as seen in the distribution of microfilarial density among people in an endemic area, the problem becomes more complicated. As a general formula, the number of person to be infected in one season is determined by : Σ^^∞__<U=1> N_U[1-(1-S)^U], where N_U is the number of persons bitten by U (Number) mosquitoes per season. The answer to this formula can be obtained by observation of the pattern of frequency distribution of N_U.

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An ecological study was made on overwintering mosquitoes in Aichi Prefecture, central part of Japan, during the period November, 1968 to May, 1969. The primary purpose of this report is to analyze some aspects of population dynamics of overwintering house mosquito, Culex pipiens pallens, thereby to contribute in elucidating the analogous problems with C. tritaeniorhynchus, the main vector of Japanes encephalitis in Japan. The results are as follows : 1) The number of females captured during the present investigation was 900, of which about 67% were C. pipiens pallens, 13% were C. hayashii, and the rest were Anopheles sinensis, C. orientalis and C. vorax in decreasing order (Table 1). 2) Mosquito associations in nine caves were classified according to dominant species. As a result, they fell into three groups : (a) Association in which C. pipiens pallens was the dominant species, (b) association in which C. hayashii and C. pipiens pallens were dominant, and (c) association in which C. hayashii and C. orientalis were dominant (Table 2 and Fig.2). 3) The number of overwintering C. pipiens pallens resting on the inside wall of the cave was at its maximum in January, then decreased markedly late in February and became to nil in April (Table 4 and Fig.3). 4) Wing length distributions of the overwintering C. pipiens pallens females did not prove to be the normal patterns, whereas those of wild-caught summer populations showed the normal ones (Figs.4, 5). Using probability paper analysis for polymodal frequency distributions (Harding, 1949), the overwintering female populations were found to include two different component groups with regard to wing length; one was a long-winged group which accounted for about 90% of all the population, and the other was a short-winged group making up 10% (Figs.6, 7 and Table 5). 5) Each of the long-and short-winged groups was assumed to be a population exclusively composed of C. pipiens pallens, on the bases of combination of ommatidial number (Table 6) and absence during nursing period of the autogenous sign characteristic of C. pipiens molestus. 6) Wing length fluctuations of the two series of C. pipiens pallens females were traced consecutively; one was sampled with light traps and the other derived from wild-caught pupae (Fig. 8). They were sampled in the same or nearby areas where the above-described survey had been made. As a result, it became evident that females with as long wings as the overwintering long-winged group continued to appear from October on; and the overwintering short-winged group seemed to be derived from survivors in the summer populations. 7) Survival rate of the overwintered females was estimated by a continuous nursing experiment and by statistical analyses of wing length distributions of wild-caught populations, with the result that at least some of the females were considered to have survived until July of the following year (Table 7).

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In the former report of experimental studies on the control of Tyrophagus putrescentiae in straw mats with various pesticides, it has been found that the installation of paper sheets impregnated with fenthion or fenitrothion, covering the entire upper and lower surfaces of tatami (straw mats), has seemed to be most effective and economical. The experiments reported here were carried out to determine suitable concentration of the pesticides to be impregnated to the paper sheets and their chronic toxicities. It is considered in these experiment that the sheets impregnated with 0.25%, 1.0% and 5.0% fenthion at rate of 100ml per square meter effective at least for 3 to 6 months, 6 to 8 months and more than a year, respetively. The paper sheets imprenated with fenitrothion seem to be effective for 2 months at concentration of 0.25%, for 4 months at 1% and 7 months at 5%. Results in the toxicological tests indicated that mice exposed continuously for 93 days to the sheets treated with 5% fenitrothion and 0.25% fenthion were not showed any adverse effects as compared with untreated ones. Although the sheets impregnated with 25% fenitrothion and 5% and 1% fenthion gave some toxicities to the mice exposed, these sheets were less toxic to the mice than two kinds of paper sheets which have been used practically for three to four years without any adverse effects to the occupants in the dwellings in Japan.

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A test was carried out to control the acaroid mites found in tatami (straw mats) in the dwellings during May to July in 1970, by using paper sheets impregnated with fenthion and fenitrothion, covering the entire upper and lower surface of the tatami. Results of the present test showed that the paper sheets with 0.37% dieldrin, 0.5% fenthion and 1.0% fenitrothion (100ml/m^2) produced reductions of 95% to 100%, 99% to 100%, and 100%, respectively, compared with the number of mites counted in the untreated tatami at the end of the test, two months after the installation of the sheets.

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Epidemiological surveys of Japanese encephalitis with special reference to seasonal prevalence of mosquitoes and virus isolation from Culex tritaeniorhynchus were carried out in Tsu areas, Mie Prefecture, in 1968 and 1969. For the survey of mosquito populations, light traps (black light 6 W) were operated through the night twice a week at the height of 1.5m inside a piggery of Tonomura (Fig.1). Japanese encephalitis virus isolations were weekly attempted from unfed C. tritaeniorhynchus caught in piggeries of Tonomura and Takajyaya (Fig.1). The results are summarized as follows : (1) C. tritaeniorhynchus was collected most dominantly, Anopheles sinensis came next, Aedes vexans was caught a little, and Culex pipiens pallens and Culex bitaeniorhynchus were found slightly from June to August as shown in Fig.2. A great number of C. tritaenioryhnchus was caught from early June to mid-July. This early increase in number of C. tritaeniorhynchus, compared with the seasonal prevalences of mosquitoes in other places of Japan, may be due to the fact that the breeding places of this species, mainly rice fields, are prepared in May in this area. (2) Despite of the great number of C. tritaeniorhynchus biting pigs in early June in this area, Japanese encephalitis was not detected from the mosquitoes until mid-July in 1968 and early July in 1969 as shown in Tables 1-4. These delayed detections of the virus may suggest the fact that the virus was not lead into amplifying cycles among pigs and mosquitoes by mid-June.

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Mice were observed in a large bottle with the atomosphere of various concentrations of chlorpicrin or hydrogen phosphide, and the lethal time for them were measured respectively. Correlation between concentrations of chlorpicrin and the lethal time for mice was according to the equation, C t=K (Haber's law), and with hydrogen phosphide, the equation, (log C) t=K, would be applied, here C : concentrations of fumigants, t : the lethal time for mice, K : constant.

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