The segregation of the siphonal hair types in the 4-4 true bred population of the autogenous strain is observed from F_1 through F_10. It seems that a pure strain concerned with the siphonal hair type cannot be obtained even though the selection is continued further. The maximum frequency of type 4-4 in the type 4-4 true bred population is estimated as about 80%, if a sufficient number of egg rafts are observed. These values seem to be same as or similar to those obtained with Culex pipiens pallens. In many cases in the progeny populations, the frequency of type 5-4 is higher than that of type 4-3.

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The genetics of dieldrin-resistance in the German cockroach, Blattella germanica, were studied by exposing a batch of larvae (from a single female) to dieldrin and observing percentage knockdown at various intervals. Hybrids of Denken (susceptible) and Isago (resistant) colonies were intermediate in resistance as compared to both parents. In the progeny of F_2 (by mass mating) the segregation into three types, i. e. resistant, intermediate and susceptible individuals, occured in the ration 1 : 2 : 1. In the progeny of back-crosses with F_1 (hybrids) and P (susceptible or resistant), the ratio of susceptible and resistant individuals was 1 : 1. It is therefore concluded that dieldrin-resistance in the German cockroach is mono-factorial with partial dominance. The separation and establishment of pure dieldrin-resistant and -susceptible colonies from a mixed Kanda colony was successfully achieved by making use of discriminating dosages.

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In May 1952 a black-coloured cockroach closely allied to Periplaneta fuliginosa was captured at Cape Sata, the southernmost point of Kyushu. Fortunately this female insect produced a number of progenies including both sexes. During subsequent years more specimens were secured from various small islands belonging to Kagoshima Prefecture, the Ryukyus, and Hachijo Island of the Izu-group. As the cockroach proved finally to be an undescribed species a description is given in this paper. Grateful thanks should be presented, in this occasion, to my colleagues who generously offered me additional material for this study.

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Some white-eyed larvae of Culex pipiens molestus were isolated in September, 1968, from the DDT-resistant colony which had been collected at Kawasaki, Japan in 1962. In order to find the values of crossover between the sex factor (M, m) and the white eye gene both in the white eye colony from Kawasaki (wj) and in another white eye colony (w) from Dr. A. R. Barr's laboratory, University of California, Los Angeles, U. S. A., the male mosquitoes heterozygous for the white eye gene were backcrossed with the white-eyed female mosquitoes. The crossover values for the white eye gene and the sex factor ranged between 0.32% (in 3 to 5 day-old males) and 0.7% (in 8 to 10 day-old males) in the wj colony and between 0.16% (in 3 to 5 day-old males) and 0.34% (in 8 to 10 day-old males) in the w colony, indicating that both the white eye genes are located at the same crossover distance from the sex factor and the crossover value for the sex factor and the white eye gene was insignificantly higher in the older male mosquitoes of both the white eye colonies.

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For the purpose of estimating the elapsed time after blood sucking, saline extracts of mosquitoes were prepared serially following a blood meal, and were examined spectrophotometrically at optical densities of 280mμ (protein band) and 410mμ (Soret band). The value of the OD 410mμ readings fell rapidly while those at an OD 280mμ fell gradually. The value of log OD 410mμ/OD 280mμ (Y) was found to be a parameter of the elapsed time. In two experiments with mouse blood in Aedes aegypti at 25℃. the values obtained from the graphed regression line were Y=-0.0134t+0.414 with r=-0.953. and Y=0.0132t+0.422 with r=-0.969 respectively, where Y represents the above mentioned logarithmic value, t the time in hours, and r the correlation coefficient between them. Results obtained with human blood in Aedes aegypti were Y=-0.0106t+0.459, and r=-0.948 and in Culex tritaeniorhynchus were Y=-0.0089t+0.372 with an r value of -0.874. The regression lines obtained varied with the type of ingested blood and with the species of mosquitos tested. Since there were some variations in the logarithmic values obtained from the same mosquitoes at any one time, an exact estimation of the elapsed time after blood sucking could not be calculated for individual mosquitoes. The values of the correlation coefficients were large enough to permit the estimation of the blood sucking activity in a wild population of a certain species of mosquitoes.

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Truck trap collections were made to analyze the mosquito populations in a rural area of Gunma Prefecture during the period from the beginning of May to the beginning of October 1965. The trap was a similar type to that reported by Bidlingmayer (1966) and mounted on the roof of a small vehicle. It had a 110×80cm frontal opening, 175cm length and a 15×15cm rear opening where a nylon net was fixed to collect insect specimens. Operations were made for about 3 hours after sunset along the paths through villages and rice fields on 2 successive evenings in every week. The vehicle was driven at a velocity of 25-30 km/h. Eight species of mosquitoes were collected through the survey and the seasonal abundance of the 4 major species (Aedes vexans, Anopheles sinensis, Culex pipiens and Culex tritaeniorhynchus) were compared as shown in Fig.2. The transitions of physiological age of female mosquitoes were also studied for the 4 species dividing into 3 categories ; empty parous, blooded or gravid, and empty nulliparous. The parity of the mosquitoes were not markedly advanced at the latter part of the survey for all species, but the 3-4 week cyclic fluctuations seemed to be recognized for first 2 months in Aedes vexans and Anopheles sinensis. Culex pipiens had a relatively higher constitution of the blooded-gravid group than that in other species throughout the survey period due to chiefly the predominance of gravid specimens. Anopheles sinensis had, on the contrary, larger number of specimens with sackshaped dilatation at the pedicel of ovarioles among the empty parous group which indicate the immediateness after the oviposition. These findings may give some clew to our knowledge on the flight activity of the mosquitoes in regard to the oviposition behavior.

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As a part of a series of studies on ecology of Culex tritaeniorhynchus summorosus, the principal vector of Japanese encephalitis, observations were made in the summer of 1967 and 1968 in Okayama Prefecture on the resting behavior of the females before and after taking blood from pig or man. Two methods were mainly used, collection and counting of the mosquitos trapped on the surface of adhesive fly catcher ribbons, and those on resting temporarily on plane paper tapes or on walls. The ribbons and tapes were set at distances of 1m, 2m, 4m, 8m, 16m and 32m from the pig. The females were found to make frequent stops on various surface near host both before and after taking blood meal, and the numbers of unengorged mosquitos according to the hours showed rather flat distributions with the peak during early hour of night, while those of engorged mosquitos showed rather sharply pointed curve with the peak at about 3 a.m., as shown in Figs 1 and 2. Since the count on the adhesive tapes represented the cumulative number of the mosquitos stopped on the surface during certain period of time (one hour in these experiments), its ratio to the counts on non-adhesive tapes was considered as an indicator of the average resting time of the mosquitos during the hour. As the average of all night, the resting time of unengorged females was estimated to be 13 minutes, while those engorged was 34 minutes in C. t. summorosus, (In Anopheles sinensis, the figures were longer in general, 38 and 68 minutes respectively). The resting time varied according to the hour, and was estimated to be the longest at around midnight in the unengorged, and at 1-3 a.m. in the engorged mosquitos. The results roughly coincided with those obtained from direct observations of mosquitos resting on the wall of a pigsty. In the comparative study on the relationships between mosquito counts on the ribbons or tapes set at various distances from the blood source, it was demonstrated that the unengorged females were more concentrated to sites closer to the host, while the highest density of those after engorged was on the surface at about 2-4 meters distant from the blood source.

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A series of studies on the seasonal prevalence of Japanese encephalitis virus in relation to the most important vector mosquito, Culex tritaeniorhynchus summorosus, have been conducted since 1965. Five pigpens, two cowhouses and the Toyama Airport, located near the paddy field zone in Toyama Prefecture, have been selected as experimental sites. The results and conclusion are summarized as follows : The prevailing season for the vector mosquito population was, in general, from late July to late August. Numbers of mosquitoes, however, have decreased with the increase of early rice crop in recent years. This pattern seemed to have been affected by helicopter-spraying of the insecticides against rice insects. In 1968, for instance, a spray test with 1.5% carbaryl (0.3kg/acre) at the beginning of August resulted in keeping the vector mosquito population under control, although the mosquitoes still became infected with the virus from the 5th to 26th of August and the virus isolation rate was still high. That is, the vector mosquito population was so small and so was that of infected mosquitoes in 1968. This may explain that the population of swine infected with the virus never reached to 100% and that there was no virologically or serologically diagnosed human Japanese encephalitis cases in Toyama Prefecture in 1968. No attempt has been made in this country to control the adult mosquitoes in paddy fields. It is conceivable, however, that an extensive aerial application of insecticides such as carbaryl over the dry paddy fields for early rice crop, ordinarily seen in Toyama Prefecture, at the time when mosquitoes become infected with the virus, results in much reduction of the vector mosquito population and Japanese encephalitis virus.

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1) Studies were carried out on (1) the effects of two new organo-phosphorus insecticides, Abate and Dursban, on larvae and adults mosquitos, (2) their cross-resistance or -tolerance to the other chemicals, and (3) their toxicity to the guppy, Lebistes reticulatus and the top-minnow, Gambusia affinis. 2) The toxicity of Abate to the larvae of C. p. fatigans, C. p. molestus and C. tritaeniorhynchus was on the same level as fenthion or higher than the chemical. Dursban on the same species were several times as toxic as Abate to the above species. The effects of these two chemicals on Aedes aegypti were inferior to those on culicine larvae. It is suspected that the colony of A. aegypti used in the present study was more or less resistant to these chemicals. 3) Diazinon-, fenitrothion-, malathion-, and DDT-selected strains of the C. pipiens group showed no cross-resistance to Abate nor to Dursban. 4) The LC-50 value for Abate in tap water with free chlorine was estimated to be several times as high as in deionized water. It seems that Abate has been decomposed by free chlorine into less toxic compounds. 5) The insecticidal effect of Dursban on both larvae and adults of the mosquitos was the most rapid of five OP compounds tested. When adult mosquitos were brought into contact to the residue of Abate, only 2 individuals out of 40 could be knocked down after continuous contact for 24 hours. 6) The LD-50 volues determined by topical application tests with the C. pipiens group were 0.025〜0.027μg/mosquito for Abate, having almost the same toxicity as diazinon and malathion, and 0.0034〜0.0050μg for Dursban, which is several times as effective as Abate and yet less effective than fenthion and fenitrothion. 7) The LC-50 values for Dursban were 0.2 ppm in toe top-minnow, (Gambsia affinis), and 0.06 ppm in the guppy (Lebistes reticulatus), being fairly toxic to the fish. The LC-50 values for Abate was 15 ppm in the top-minnow and 5 ppm in the guppy, and was less toxic than Dursban.

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In 1968 and 1969, laboratory studies were conducted with German cockroaches, Blattella germanica (L.), to determine their susceptibility level to lindane, diazinon, fenitrothion and fenthion. Cockroaches collected from 13 localities in Kyushu, Japan, i. e. Nakazu, Tenjin, Ohhashi, Hakata A, Hakata B, Nakatsu, Nobeoka, Miyazaki, Abutatsu, Kagoshima, Ibusuki, Saga and Isahaya, were compared with a susceptible laboratory colony for determining their resistance level by knockdown tests. The configuration ratio of three phenotypes in lindane resistance, i. e. homozygous susceptibles (SS), heterozygous hybrids (RS) and homozygous resistants (RR), was detected from the plateaux demonstrated on a log time-probit percentage knockdown line. Susceptibility to three organophosphorus insecticides was also assessed by knockdown time and mortality after contact to the residues. All the populations tested have shown high resistance to lindane, and they were proved to be almost susceptible to diazinon, fenitrothion and fenthion, though a few individuals in Nakazu and Aburatsu populations were suspected to be more or less resistant.

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In the course of field studies on epidemiology of japanese encephalitis in Okayama Prefecture, two dry ice traps using mosquito net were used at about weekly intervals in the purpose of collecting nocturnally active mosquitos, during the periods from May 22 to October 16, 1967, and from May 24 to September 11, 1968. The traps were operated for two and half hours from 30 minutes before the sunset, and the mosquitos attracted to the carbon dioxide source were allowed to enter into the mosquito nets. Besides large numbers of mosquitos (altogether 9 species) reported in separate papers, the following 13 species (64 specimens) of tabanid flies were also trapped. The above results are interesting in that the tabanid flies, including rather rare species, are collectable during the night time with the simple dry ice mosquito traps, though they have been known to be attracted to carbon dioxide during the daytime. 1) Chrysops vanderwulpi, 19 specimens, 2) Atylotus horvathi, 23 specimens, 3) Tabanus exoticus, 1 specimen, 4) T. trigonus 3 specimens, 5) T. shikokuensis, 4 specimens, 6) T. coquilletti, 5 specimens, 7) T. administrans, 1 specimen, 8) T. fuluimedioides, 2 specimens, 9) T. iyoensis, 1 specimen, 10) T. amaenus, 1 specimen, 11) T. takasagoensis, 1 specimen, 12) Tabanus sp. (I), 1 specimen, 13) Tabanus sp. (II), 2 specimens.

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Several strains of house flies were tested in a box (0.5m^3) to evaluate the relative effectiveness of three pyrethroids. The following strains were used as test insects. 1. Tatara (Highly r-BHC-and dieldrin-resistant) 2. Takatsuki (susceptible) 3. Lab-em-7-em (susceptible) 4. 213-ab (D D T-and pyrethrins-resistant) 5. RP (diazinon-resistant) 6. P-9 (diazinon-resistant) 7. Py (pyrethrins-resistant) 8. CSMA (susceptible) The order of resistance levels based on the KT-50 valus for three pyrethroids were as follows. Pyrethrins : Py>RP>P-9>Lab-em-7-em>213-ab>Takatsuki>CSMA>Tatara. Allethrin : 213-ab>Takatsuki>Py>CSMA>RP>Lab-em-7-em>P-9>Tatara. Phthalthrin : Takatsuki>213-ab>RP>Lab-em-7-em>Py>CSMA>P-9>Tatara. The quantites of allethrin penetration through the cuticlar layer of the house fly were determined by means of Gas-chromatrography.

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