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[in Japanese]

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The segregation of the siphonal hair types was observed in the progenies which were produced by the parent populations composed of type 5-5 of the siphonal hair type in Culex pipiens molestus (Tables 3 and 4). When the selection progressed; the frequency of type 4-4 decreased; that of 5-4 fluctuated between 11.3 and 44.5%; that of type 5-5 increased; and the types other than the above did not occur. Viability of the type 5-5 population decreased so as not to yield the 11th generation.

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The survival and longevity of both male and female Culex mosquitoes, C. pipiens and C. tritaeniorhynchus, when offered flowers of some nectar plants were observed in the laboratory under the conditions of room temperature during the period from April to September, 1970. Four nectar plants, such as rape (Brassica napus L., Cruciferae), milk vetch (Astragalus sinicus L., Leguminosae), white clover (Trifolium repens L., Leguminosae) and sorrel vine (Cayratia japonica Gagn., Vitaceae) were used respectively as nectar sources for the insects. The flowers of them were gathered every day from the field and put in the mosquito cage of 30cm cube in which a lot of the mosquitoes have just started the adult stage and, on the other hand, water and 0.5% cane sugar solution were given severally to another cage as a control for the nectar feedings. The flower, water and sugar solution were renewed every morning and all dead mosquitoes which lay down every cage were removed and counted. At the same time with the above experiments, the survival and longevity of blood-fed mosquitoes were observed to make clear effects of blood meal on the length of life of the insects. Briefly summarizing, it was found from the data presented that, when the mosquitoes were given flowers tested except white clover, longevity prolonged exceedingly as compared with the control specimens received plain water only, although female adults which had been fed on sugar were able to survive for the longest periods, 5-20 days (2-4 days in male) longer in the mean life duration than adults which had been offered nectars. The maximum life spans of the female adults were 25 days in rape and more than one month in both milk vetch and sorrel vine feedings respectively and, in the life span, the latter two were almost equal to that of the adults which had been fed on sugar. Male adults showed a less life span than females, about two weeks in general in the cases of nectar feeding. The survivorship curves of both male and female mosquitoes which had been offered white clover were almost similar to that of the insects received plain water only and almost all died within a week or so owing probably to too short proboscis to sup nectar of the flower. In the blood feeding tests it was found that, when the mosquitoes were fed on mice, most of them, 70-80% or more, could survive until 3-4 days after taking the blood but rapidly died within a week after that and, even in a case of the double blood feedings, survivorship curve was almost unchanged although 3-4 days longer in the life span than the former which was offered single blood meal. It seems to be obvious accordingly that blood meal is not sufficient to maintain life beyond several days for the most adult mosquitoes and they have to take nectar or some sugarcontaining fluids other than blood to maintain existence for long periods.

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The two mosquito species, widely distributed in Japan, Culex triteaniorhynchus summorosus Dyar and Culex pseudovishnui Colless, are closely related and difficult to be differenciated in adults (especially in females), and therefore most of the ecological studies carried out in the past in relation to the transmission of Japanese encephalitis made observations with the mixed populations of the two species. Since the author and his colleagues recently elucidated that they could be clearly differenciated by the presence or absence of erect white scales on the vertex of adults, detailed observations on differences in ecology of the two species were carried out in a hilly area of Okayama Prefecture, western Honshu, where relative population density of the latter was high. The seasonal changes in the population density of adults of the above two species were investigated by weekly collections with black-light traps, dry ice traps using mosquito net, and by those with sucking tubes in animal houses. Quantitative collections of immature stages from the breeding places were carried out also at stations selected from rice paddies located on a hill slope. The difference between the two species were most clearly seen in the seasonal changes in the larval population; C.t.s. began to increase earlier from late June and reached to a peak in the end of July, while C. pv. was found to increase from mid July with the peak in mid August. Such differences in adult populations were rather obscure, but the ratio of C. pv. to C.t.s. was found to be lower in July than in June and August. The distribution of larvae in 31 quaters of rice paddies under observation has also revealed the difference in the behavior of the two species; The larvae of C.t.s. were found mainly in the lower parts of the paddies where the temperature of water was higher, while that of C. pv. were restricted more to the upper cooler waters, though both showed expansion of the territories to opposite sides at the peak seasons of population densities. The biting rhythm of female mosquitoes as observed by all-night collections from the body of cattle or pigs was found to be essentially the same between the two species, being active all through the night time with inconspicuous peaks of the activity at around 9 p.m. and 2 a.m. and was shown to be essentially different from that of the Culex pipiens complex of mosquitoes which was demonstrated previously to be active with a peak at midnight. The total numbers of adults collected during this season were higher in ratios of P. pv. to C.t.s. with the animal baited traps than with the dry ice or blacklight traps. As for the attractiveness among the animals, the ratio of C. pv. to C.t.s. was higher on cattle than on pigs. In observations made with mosquito net traps baited with man and pig, both species were attracted more to the pig than to man, but the ratios among the total mosquito species collected were about twice higher on pigs in C.t.s. than in C. pv.

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An ecological study was made on the larval and imaginal populations of medically important mosquitoes in Nagoya district during a period from April to November, 1968. The purposes of this report are to estimate relative abundance of newly emerged adults at population level from the view points of seasonal change of larval population size and larval age structure in paddy fields, and to know relation between the above population dynamics of larvae and seasonal prevalence of adult mosquitoes in the vicinity of the paddy fields. 1) The number of larvae and pupae in the paddy fields was estimated by the removal method, and totaled 2, 423 during the study period. Dominant species, Culex pipiens pallens, accounted for more than 50%, C. tritaeniorhynchus for about 26% and the rest were C. orientalis, Anopheles sinensis and C. vishnui in decreasing order (Table 1). In the vicinity of the paddy fields, 1, 101 adult mosquitoes were captured by a light trap. They consisted of about 64% C. pipiens pallens, 23% C. tritaeniorhynchus and 13% An. sinensis, Aedes vexans nipponii, C. orientalis and C. hayashii (Table 2). 2) The larval population of C. tritaeniorhynchus occurred from mid June to late October, and the population size reached its peak early in July. From the consecutive analyses of larval age structure, adult emergence at population level was recognized four times (Fig.3), and newly emerged adults were estimated to be most abundant at the second emergence time (around the early part of July) on the basis of the precursory abundance of the fourth instar larvae and pupae. On the other hand, imaginal population of the species occurred from late June to late September. And the population size reached its maximum in late July, about two weeks after the preexisted maximum adult production in the larval population (Fig. 3). 3) The larval population of An. sinensis occurred from mid June to early October, and the population size was at its peak early in July. From the consecutive age structure analyses, adult emergence at population level was recognized three to four times (Fig. 3), and newly emerged adults seemed to be most abundant at the second emergence time (about the early part of July). Imaginal population of the species was occurred from early June to early September, and the population size reached its highest peak in late July, about two weeks after the maximum adult production in the larval population (Fig. 3). 4) The larval population of C. pipiens pallens occurred during mid June and mid July, and the highest population peak was observed in early July. Adult emergence at population level was recognized only for a short period as the result of the age structure analyses, and newly emerged adults seemed to be most abundant in late July (Fig. 3). In spite of the relatively short prevalence period of larval population in paddy fields, imaginal population of this species occurred during a long period from late April through mid October. This phenomenon seems due to the fact that the larval populations of this species usually prevail throughout the spring-autumn seasons in many a fertilizer pit in and around the area under the present investigation. The imaginal population size, however, was observed to reach its peaks shortly after the maximum adult production in the larval population was seen in the paddy fields (Fig. 3).

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Culex tritaeniorhynchus Giles was collected by light traps through the night in cowsheds and pigpens. There was a linear relation between the number of mosquitoes trapped in the outside of a cowshed and the number of mosquitoes in the cowshed (Fig.1). The blood feeding rates decreased depending on the number of mosquitoes per one cow or swine. (Fig.2, 3 and 4). Percent ratios of females with a trace amount of blood meal among entire blood-fed populations increased in accordance with the increase of population densities (Table 1). This suggests that the interference among individual mosquito has an important role when mosquitoes exist abundantly. In every collections, the blood feeding rates of both nulliparous and parous females decreased depending on the number of mosquitoes. But when the number of mosquitoes was over 5, 000, the blood feeding rates of parous females. (Fig.5). When the number of mosquitoes was over 15, 000, the estimated number of parous females began to decrease in a cowshed (Fig.7), but in a paddy fiield, the estimated number of parous females collected by a dryice light trap did not decrease even when the number of mosquitoes was 78, 152 (Table 2). An estimation was thus made that unlliparous females may disperse if the number of mosquitoes was over 5, 000, and parous females may also disperse when the number of mosquitoes increased over 15, 000.

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Observation of nocturnal flight activity of Culex tritaeniorhynchus was carried out by means of hourly collection in a light trap and the dissection of the females. The diurnal changes of C. tritaeniorhynchus showed a bimodal pattern and the height of two peaks fluctuated regularly according to population trend. When numbers caught through the night increased, numbers in the first peak increased remarkable but those in the second peak slightly. The proportion of numbers in the first peak for numbers caught through the night increased to almost 90%. The parous rate at 19-20hrs. was lower than that at 03-04hrs, and in parous females caught at 03-04hrs. there were many individuals that the condition of the connecting stalk of follicle showed sac like. These observations suggest that the age-composition fluctuates through the night in nocturnal flight activity of female population.

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A comparison was made on the body weight and embryo size of the Norway rat (Rattus norvegicus) captured from five areas, a refuge dump, a henhouse, a pigpen, shopping and residential quarters in Kanagawa Prefecture, during a period from 1965 to 1940. For the determination of age of rats, molar wears were calculated from wear areas of one upper molar row. The results were summarized as follows; 1) There was a high correlation between the body weight and molar wear in both sexes in each population. According to the regression lines of the log. of body weight on the log. of molar wear, rats from the dump and the henhouse showed the heaviest and others were successively following order; the pigpen, shopping and residential quarters. 2) The pregnant females appeared from about 3.0(mm)^2 or more of molar wear in any populations surveyed. On the other hand, body weights of pregnant females were different in each population, i.e. 160g or more for the dump and the henhouse, 140g or more for the pigpen, 120g or more shopping quarters and 100g or more for residential quarters respectively. 3) The mean embryo size was significantly larger in the dump (9.97) and the hanhouse (9.79) than in the pigpen (8.30) and shopping quarters (8.25). 4) These differences detected would be caused by differences of environmental conditions, especially quantity and quality of foods available and social tension of the population.

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Field examinations were conducted to evaluate effects of the application poison baits (formulations have been improved by Tsuji and Ono, 1969 & 1970) on the field population of the smoky brown cockroach, Periplaneta fuliginosa, in a mouse breeding room (Station A) and 3 adjacent rooms (Station B, C, & D) in a building near the down town Toyama City. After the bait application (5g granules per 2.5m^2), the population looked markedly decreased and many dead bodies were found in the experimental station. Using a marking method, for example, the population is Station A was estimated at about 5, 000 before the bait application. This dramatically decreased to only about 20 within 6 weeks after the treatment (estimated by the decreasing rate of the dead bodies). The age distribution of the cockroach in Station A was markedly affected by the bait application and the proportion of younger nymphs, especially that of the first instar ones, became strikingly high. This probably is due to the appearance of the first instar nymphs from the oothecae which had already been deposited before the bait application. In Station D, on the other hand, which was 20 meter apart from Station A and was not treated with the bait, the age distribution remained unchanged and almost no cockroaches were found dead. There was a tendency that younger nymphs were found dead near the bait, whereas adults and older nymphs died distant from them. The usual activity range of adults seemed to be within 100m^2, while that of younger nymphs to be more restricted. Therefore it seems possible to control the cockroach even in an arbitrary given area.

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The acaroid mite Tyrophagus putrescentiae has become a common household pest in recent years in Japan as it breeds and reaches to tremendous population densities in "tatami", or the rice straw mats commonly used as the floor material in this country. A series of laboratory and field experiments were carried out for the purpose to find out effective methods for its control by the use of pesticides now available to us. Among various methods tested by us for the control of mites in tatami, the installation of paper sheets impregnated with the pesticides covering the entire upper and lower surfaces was found to be most effective and economical. Among the pesticides tested, fenthion and fenitrothion gave most satisfactory results. As for the fumigants to be applied in a room or the spray materials to be applied directly on the surface of mite-breeding tatami, trichlorobenzene, nitrochlorotoluene, xylenol, phenol and metacresol were shown to be effective at relatively high concentrations.

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