Japanese Encephalitis Vectors

On the ecological basis of vector mosquitoes of Japanese encephalitis, measures of their control were examined from viewpoint of their practicability. It was concluded that chemical control is not of practical value, biological control is of limited effectiveness, and environmental control by source reduction is impossible. Instead, it was recommended to improve human living style so as to reduce the frequency of man/mosquito contact

The verbosus Group of the Genus Culicoides Latreille (Diptera: Ceratopogonidae) in Japan, with Descriptions of Three New Species and One Hitherto Unknown Male.

The verbosus group of the genus Culicoides distributed in Japan was reviewed. Three new species and one hitherto unknown male were figured and described, and a key was given to the females of all 13 species in Japan

蚊によるバンクロフト糸状虫症伝搬の危険性に影響する要因について

The transmissibility of bancroftian filariasis by a vector mosquito, in other words, the epidemiological danger of filariasis infection due to the mosquito to persons in a community is very important to understand the dynamic states of the disease. It may be expressed by the product of three factors the effective microfilarial prevalence corrected considering the microfilarial density, the effective period of transmission, and the abundance of mosquitoes during the effective period. The epidemiological danger was estimated by using the data obtained in field experiments carried out from 1961 to 1967 at Nagate and Okubo Villages, Nagasaki Prefecture, Japan, under the changing conditions in microfilarial prevalence and density due to the control of vector mosquitoes or the treatment of positive persons by drugs.ある部落におけるバンクロフト糸状虫症の蚊による伝搬性,即ち人間に対するフィラリア症感染の疫学的危険性は本病の動的様相を理解する上で極めて重要である.これは次の3つの要因の積として表わし得る:(1)仔虫数によって修正した有効仔虫保有率,(2)有効伝搬期間,(3)有効伝搬期間中の蚊の多少.これら3つの要因について,伝搬蚊の駆除あるいは患者に対する投薬によって仔虫保有率が変化しつつある長手及び大久保部落で得られた値を用い,疫学的危険性を吟味した

種々の条件下でのコガタアカイエカの栄養生殖分離

In order to understand the ecological significance for the gonotrophic dissociation in Culex tritaeniorhynchus summorosus females, the development of follicles, the activity of blood feeding and the incidence of gonotrophic dissociation were examined with the females which had been reared as adults under the outdoor natural or indoor experimental conditions and with those which had been caught at cowsheds. From the results obtained, it was indicated that under the conditions of the short day-length the gonotrophic dissociation occurs commonly, however the feeding rate is very low and accordingly the number itself of the females showing this phenomenon is very small. Therefore, it can be said that the gonotrcphic dissociation in this species does not play the important role on the overwintering ecology.コガタアカイエカの栄養生殖分離の果す生態学的意義を明らかにするために,夏から秋にかけて屋外の自然条件下で飼育羽化させた雌及び種々の日長と温度とを組み合せた実験条件下で飼育羽化させた雌について,濾胞の発育状態,吸血率及び栄養生殖分離率を調査し,更に春から秋にかけて牛舎で採集した吸血雌についても栄養生殖分離率を調べた.これらの調査結果から,本種雌の栄養生殖分種は短日条件下で普通に起こるが,吸血率が顕著に低いため,本現象を示す雌の数は極めて少ないことがわかった.したがって,本種の栄養生殖分離が越冬生態の上に重要な役割を果すとは思われない

日本脳炎伝搬蚊,特にコガタアカイエカの生態 : 4.コガタアカイエカの未成熟期の発育と特に春と秋における温度との関係

Eggs of Culex tritaeniorhynchus summorosus laid by wild-caught and laboratorycolonized females were reared to adults under outdoor natural conditions particularly in spring and autumn, and the relation of the developmental period of immature stages of the mosquito to the extrinsic temperature was given. The results indicated that the developmental speed of immature stages given as the reciprocal of period decreases clearly with the drop of temperature and the development hardly occurs at the temperature below about 16℃.野外で採集した,または実験室で累代飼育中のコガタアカイエカ雌成虫が産んだ卵を,屋外飼育室の自然条件下で特に春及び秋に成虫にでま飼育して,温度と未成熟期の発育期間との関係を求めた.その結果,発育日数の逆数として求めた発育速度は,温度の低下と共に顕著におそくなり,約16℃以下では殆んど発育しないことがわかった

柄杓のコガタアカイエカ幼虫採集能率

The efficiency of the dipper (15 cm diameter and 3 cm depth) in collecting immature stages of Culex tritaeniorhynchus summorosus was examined experimentally in July, 1971. In each of four water tanks (85×85 cm, water depth 10 cm) in which rice plants were growing, 100 each of first, second, third, and fourth instar larvae and pupae of tritaeniorhynchus were released, and four persons dipped the water at ten sites in each water tank by the dipper (therefore the number of dips was 160 in total); in each dip the collected larvae were counted by instar, and then returned to the same site as the dip was taken. Based on the figures obtained by the above experiment, the dipping efficiency, which was defined as the probability for one larva in 1m^2 to be collected by one dip, was established for each instar. By using this dipping efficiency it became possible to estimate the absolute density of tritaeniorhynchus larvae from the mean number per dip and the area of the rice field under study.20株の稲(高さ約65cm)が植えてあるコンクリート製水槽(85×85cm,水深10cm)4つの各々に,コガタアカイエカの1～4令幼虫及び蛹をそれぞれ100個体(合計500個体)ずつ放した.これらの水槽で,柄杓(直径15cm,深さ3cm)を用いてすくいとって令別個体教を記録した後,すくいとられた幼虫を水槽のもとの位置にもどした.これを各水槽において4人でそれぞれ10回ずつくり返した.このようにして4つの水槽で合計160回すくいとった結果597個体(1すくい平均3.73個体)の幼虫(蛹を含む)が得られた.最初に85×85cmの水槽に各令幼虫及び蛹併せて500個体放したので,1m^2当り500/0.85^2=692個体いた水槽からすくいとったことになる.即ち,1すくい当り平均3.73個体の幼虫が得られる時には,Im^2当りの幼虫密度は約692個体と推定される.また,1すくい当り平均1個体が得られたとすると,幼虫密度は1m^2当り692/3.73=186個体となる.この関係を用いれば,実際に水田ですくいとった柄杓当りの平均幼虫数から,1m^2当りの幼虫数を推定することができ,これに対象とした水田の面積を掛けることによって,そこに生息している幼虫の絶対数の推定値を得ることが可能となる.以上は各令幼虫及び蛹を合計した値を用いた結果であるが,各令別にも同様の計算をすることができる

水田地帯におけるコガタアカイエカ幼虫の空間分布

Spatial distribution of Culex tritaeniorhynchus summorosus larvae was studied in a rice field area surrounded by low hills, common in Nagasaki Prefecture. Rice fields in the area were about 15 hectares (roughly 500 rice fields), and among them 100 rice fields made of 11 groups were selected as study plots from various parts of the area. The study was done from May to October and the results were as follows. Larvae of Culex tritaeniorhynchus summorosus tended to concentrate in rice fields situated in some part of the whole area at a certain time and the position of such part changed during the period of mosquito occurence. Moreover the density level differed, sometimes markedly, among rice fields situated closely in a same group. These results are interesting in relation to the population study of this mosquito. Firstly, they ascertain our previous report that the number of rice fields examined should be increased, even though the number of dips taken from a rice field is decrease to only one, for estimating the relative density of the whole area in maximum efficiency. Secondly, they show that one rice field should be considered as one of natural unit for larval population in a rice field area. The latter seems to be very significant for understanding the processes of population fluctuation of this species, for density effects by overcrowding of larvae may act in some rice fields, while density in many other rice fields is remained low.長崎県に多い山間の水田地帯で,コガタアカイエカ幼虫の空間分布を調査した.調査地にある約15ヘクタール(およそ500枚)の水田のいろいろの部分から全部で100枚の水田を選び,5月から10月まで,原則として週に1回調査をした.その結果,コガタアカイエカ幼虫の密度の高い水田は,ある調査日には特定の場所に集中している傾向があること,その場所の位置は調査日ごとに変化していくこと,更に,隣合った水田で幼虫密度が著しくちがうことも珍しくないことが明らかになった.この結果は,広い地域のコガタアカイエカ幼虫の密度を知るためには,その地域内のいろいろの場所でなるべく多くの水田を調査しなければならないこと,及び,コガタアカイエカ幼虫個体群にとっては,個々の水田が1つの小単位となっていることを示している.後者は,コガタアカイエカの個体数変動の過程を解明していく上で極めて大切な観点であると思われる.何故ならば,大部分の水田の幼虫密度が低い時でも,一部の水田では過密による密度効果が働く可能性があるからである

Effect of Lipopolysaccharide on the Duration of Zolpidem-Induced Loss of Righting Reflex in Mice

Zolpidem, a non-benzodiazepine hypnotic, is primarily used to treat insomnia. In a previous study, pior treatment with non-benzodiazepine receptor agonists was associated with inflammation. The present study aimed to clarify the association between the effects of zolpidem and inflammation in mice treated with lipopolysaccharide (LPS), a known model of inflammation. We assessed the zolpidem-induced loss of righting reflex (LORR) duration 24 h after LPS treatment in mice. Additionally, the expressions of γ-aminobutyric acid (GABA)A receptor subunit and K+-Cl− cotransporter isoform 2 (KCC2) mRNA in the hippocampus and frontal cortex were examined in LPS-treated mice. Pretreatment with LPS was associated with significantly prolonged duration of zolpidem-induced LORR compared to control mice. This effect was significantly attenuated by administering bicuculline, a GABAA receptor antagonist, or flumazenil, a benzodiazepine receptor antagonist, in LPS-treated mice. Compared to controls, LPS-treated mice showed no significant change in the expression of GABAA receptor subunits in the hippocampus or frontal cortex. Bumetanide, an Na+-K+-2Cl− cotransporter isoform 1 blocker, attenuated the extended duration of zolpidem-induced LORR observed in LPS-treated mice. LPS significantly decreased Kcc2 mRNA expression in the hippocampus and the frontal cortex. These findings suggest that inflammation increases zolpidem-induced LORR, possibly through a reduction in KCC2 expression

Transmission Dynamics of Dirofilaria immitis in a Southwestern Part of Japan

The transmission dynamics of Dirofilaria immitis were studied by using reported data in Nagasaki City and Omura City, Japan. The catalytic model was applied to the age distribution of positive rate for microfilariae of D. immitis in dogs. Using the force of infection obtained by applying the catalytic model, the critical vector density for the disappearance of D. immitis was estimated. Transmission frequencies of D. immitis in the two places were calculated by densities and infective rates of the principal vector, Culex pipiens pallens, and numbers of infective larvae of D. immitis in the vector. Roles of some factors influencing the transmission frequency of D. immitis were also evaluated with a simple mathematical model, and it was concluded that the continuation of extensive infection with D. immitis in dogs in spite of the presumed decrease of the vector density in recent years is ascribable to the increase of dog density and the increased protection of humans from mosquito bites