The lethal doses and the feeding preference of scilliroside baits to Norway rats, Rattus norvegicus, were studied in the laboratory. The lethal doses of scilliroside in dry baits were higher than those in wet baits. The approximate lethal doses of scilliroside in dry baits represented per kilogramme body weight of the rats were as follows : male 3.1mg and female 1.7mg for 0.017% bait; male 1.5mg and female 1.0mg for 0.03% bait; male 1.5mg and female 1.0mg for 0.05% bait. The lethal doses in wet baits were as follows : male 1.6mg and female 1.0mg for 0.017% bait; male 1.0mg and female 1.0mg for 0.03% and 0.05% baits. Some of the rats used in the present study tended to avoid feeding dry baits at lethal doses and more males survived than the females; i.e., about 70% of the males and 30% of the females survived with 0.017% dry bait, and about 30% of the males and 15% of the females did with 0.03% and 0.05% dry baits. Some of the rats survived also with the wet baits.

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Feeding with various amount of food, "Oriental Rat Food MF powder", population equilibrium, age composition, and response of individuals to traps were investigated with experimental populations of the German cockroach, Blattella germanica L. at a constant temperature of 27±1℃ and 16 hours illumination per day (Fig. 1). When supplied with 4g, 8g or 16g of food every 30 days, or 3g every week, populations starting with 10 adult females with oothecae attained an equilibrium state within two months. The proportion of nymphs in populations in the equilibrium state was usually about 80% or more (Figs. 2,3 and 4). When an excess amount of food was given to the populations, the number of cockroaches increased almost two-fold in 10 days. The increase was largely due to that of 2nd to final-instar nymphs. Thus, the break of the equilibrium caused an increase of the nymphal proportion in the populations (Fig. 5). Catches of cockroaches in glass jar traps without bait showed a periodicity which was exactly parallel with that of the additions of new food. Peaks of the catches occurred just before the addition of new food, while the fewest catches just after it (Fig. 6). These results appear to indicate that, in controlling the German cockroach, the use of poisonous food baits may be more effective than to utilize sex pheromones which attract only adult insects.

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There was an outbreak of about 30 cases of an acute febrile exanthematic disease among school children in Yamada, a mountain village in Toyama Prefecture, northern Honshu, during March-April, 1968. Laboratory tests for various exanthematic diseases were all negative, excepting for that positive results were obtained in Weil-Felix tests with OXK in 6 of 9 sera examined. Two out of 4 sera were a also positive in the fluorescent antibody tests against rickettsia of Tsutsugamushi disease. Seasonal surveys of trombiculid mites and tests of infection with the rickettsiae of the rodent hosts were carried out in the same area during one year's period from April 1969 at intervals of about one month. In the complement fixation tests of sera collected from 34 field mice (Apodemus speciosus) trapped during May and June, 17 (65%) were positive against Rickettsia orientalis. A total of 208 Apodemus speciosus and 15 Microtus montebelli were trapped and examined from the area during the one year survey, and altogether 7,504 chiggers (trombiculid mites) were recovered from these rodent hosts and from a wild bird Troglodytes troglodytes. The chiggers were classified into 5 genera and 10 species, as shown in Table 1. The most abundant among them was Leptotrombidium fuji, which showed peaks of the density both in autumn and spring. L. pallidum, a species known as one of the vectors of Tsutsugamushi disease in Japan, was the third in the order of abundance following Gahrliepia saduski, and also showed its peaks in the spring and autumn. Although further studies are necessary for drawing final conclusion, the above observations suggest that the disease could possibly be Tsutsugamushi disease transmitted to the patients by L. pallidum.

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Trial application of discriminant function was proposed for the differentiation of three types of Culex pipiens complex, C.p. fatigans Wiedemann, 1828 (Cpf), C.p. pallens Coquillett, 1898 (Cpp) and C.p. molestus Forskal, 1778 (Cpm) in Japan. Using this method, a new approach was made to the problem whether Cpm or Cpf adults were mixed or not in "Cpp imaginal populations" captured in the open field of Nagoya City, central Japan. 1) The mean values of diagnostic characters in the specimens of Cpf (Naha strain). Cpp (Nagoya strain) and Cpm (Nagoya strain) used as a temporary standard for comparison were as follows respectively : D/V ratio of male genitalia (Fig. 2)=0.38,0.79 and 1.08; SB value (Fig. 2)=17.1,11.1 and 5.8 unit (1 unit=2.5μ); ommatidial number of female (Fig. 3)=80.0 (8.9/row), 78.6 (8.9/row) and 60.7 (7.8/row); HS value of female genitalia (Fig. 3)=22.5,21.3 and 25.6 unit (Table 1 and Figs. 2,3). 2) When x_1 denotes the D/V ratio, x_2 the SB value of male, and x_1' denotes the ommatidial number (square value of the average number per row), x_2' the HS value of female, the discriminant functions are determined as general equations, Z_m=λ_1x_1+λ_2x_2 and Z_f=λ_1x_1'+λ_2x_2' (Table 2). The discriminant values in all of the specimens were calculated by substituting corresponding values of the above characters for x_1 or x_1' and x_2 or x_2' in the respective equation. As a result, frequency distributions of these discriminant values were clearly separated from each other with only a few exceptions (Figs. 4,5). 3) The critical point of the discriminant values was fixed so that α might be equal to β for male mosquitoes, where α signified the probability of committing type I error in which Cpp might be mistaken for Cpm (or Cpf) and β signified that of type II error in which Cpm (or Cpf) might be mistaken for Cpp (Fig. 4). The rejection limit of the discriminant values of Cpp (one sided probability of type I error, α=0.01) was used as a critical point in differentiating Cpm from Cpp in the case of famale (Fig. 5). 4) Judging by the above critical discriminant values, the number of male mosquitoes morphologically identified as Cpm and Cpf was 0 and 2 (ca. 0.5%) respectively, and the number of female identified as Cpm was 2 (ca. 2%) in the Cpp imaginal populations captured in the open field (Figs. 6,7,8 and Table 3). 5) An advantage was discussed that an integrated and objective discrimination could be expected when the discriminant function derived from the quantitative diagnostic characters is properly applied to the identification of allied species. A discussion was given of supplementary use of the function as an aid to differentiate only indistinguishable individuals by one character.

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In order to verify the stages of the life history in which 4 species of cockroaches, B. germanica, P. americana, P. fuliginosa, and P. japonica should encounter the winter under unheated conditions in Central Japan, effects of 3 temperature-photoperiod combinations upon the development and reproduction of the cockroaches were investigated. The results seem to indicate that, under unheated conditions in Central Japan, most of newly hatched nymphs of the Periplaneta species will not become adult in the same year, and all developmental stages may encounter the winter, though the retardation of development in the second and/or final instar of Periplaneta species seems to restrict the stage distribution of winter populations of the species mainly to these instars. The results also suggest that a "two-year life cycle" may be rather normal, especially in P. japonica, under outdoor conditions. In B. germanica, adults and nymphs of older instars seem to be the major stages which encounter the winter.

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The top minnow, Gambusia affinis (Baird et Girard, 1853), is a viviporous poeciliid fish native of the southern United States, and has been introduced into a number of countries mainly with the purpose of malaria control. In Japan, the fish is known to be imported in 1916 via Hawaii and Taiwan, and has been found recently to be breeding widely in polluted waters in and around the city of Tokyo. The present paper deals with the results of observations on Gambusia introduced from Tokyo to Tokushima City of Shikoku Island in April 1969. Tokushima is a city situated on the delta of Yoshino River, where tremendous numbers of mosquitoes were breeding every year in swamps, ditches and rice paddies difficult to be drained. Surveys were carried out on the larval breeding places, and on the seasonal prevalence of adults with light traps set at 6 stations. Of 14 species of mosquitoes found in this area, Culex pipiens pallens was predominant and most widely distributed, while Anopheles sinensis and Culex tritaeniorhynchus were also found abundantly in some swamp areas. In some salt marshes near the sea coast, tremendous breeding of Aedes dorsalis was observed in the rainy seasons. Under such environmental conditions, it was considered by us that the introduction of Gambusia might be an effective measure for the control of mosquitoes, and two shipments of about 400 fishes collected from sewage ditches in the Tokyo International Airport were made to Tokushima by air cargo in April and May, 1969. The fishes were released and bred first in certain ponds and pools, and were further distributed to other ponds, swamps and ditches from the autumn of 1969. Especially successful and effective was the culture of Gambusia in the salt water marshes where Aedes dorsalis had been breeding; from August 1970,one year after the first batch of some 500 fishes were released, they became visible in high population densities all over the swamps, and thereafter complete eradication of the mosquito larvae could be achieved from these areas. Field and laboratory studies were made with Gambusia thus successfully established in large number of pools in and around this city. The results are described in this report on its distribution, the trend of increase in the population densities, the competition with the indigenous fishes such as Oryzias latipes, the capacity as a predator of mosquito larvae, the correlation of the number of youngs borne with the body size of the mother fishes, the intervals of the births, the resistance to the cold temperature and to various poisonous substances in water, etc.

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The morphological features of male accessory gland which were devided into three zones to take for convenience as in Fig. 1,were observed by electron microscope. The gland is surrounded by a thin muscle layer which has the basement membrane on both outer and inner surfaces. The spermatozoa and secretion granules can be seen in the luminal space from anterior zone to posterior zone. Secretion granules are also seen in the epithelial cells and classified in three types; A, B and C. A type granules, which vary in size and shape, are bounded by a membrane and consist of electron dense part and vacuole part. B type granules, which are surrounded by a membrane, have electron dense round, rarely amorphous region in the center of these granules and less dense part around the dense region. C type granules vary in size, shape and electron density. The epitherial cells which consist of a single layer are devided into four types according to the types of including granules. The first type cell has A type granules and well developed granular endoplasmic reticula. This type of cell is located in all zones. The second type cell with B type granules and granular endoplasmic reticula is seen only in the posterior zone. The third type cell with C type granules and granular endoplasmic reticula is situated only in the posterior zone. The fourth type cell without granules is seen on a side of the gland wall from anterior zone to posterior zone in groups.

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Following to the former report (Harada et al., 1971), the survival and longevity of adult mosquitoes, Culex pipiens molestus and Aedes togoi, when fed on the flowers of 13 herbaceous and 5 woody plants were observed under laboratory conditions of room temperature during the period from April to September, 1971. Among the flowers of herbaceous plants tested, common vetch (Vicia sativa, Leguminosae) was most effective on the longevity of Culex, which had mean life-spans of 24 days in males and 28 days in females. The flowers of milk vetch (Astragalus sinicus, Leguminosae) which was tested with Aedes togoi was secondarily effective and the mean life-spans of them were 22 days in males and 17 days in females respectively. Rape (Brassica napus, Cruciferae), speedwell (Veronica persica, Scrophulariaceae) and sorrel vine (Cayratia japonica, Vitaceae) were all similarly effective on the survival and longevity of Culex or Aedes mosquitoes fed on these flowers and the maximum life-spans of them reached into a month or 40 days. The mosquitoes fed on the other flowers, such as dandelion (Taraxacum platycarpum, Compositae), cottonweed (Gnaphalium multiceps, Compositae) and fleabane (Erigeron philadelphicus, Compositae), reached into a month or more in their maximum life-spans but the greater parts of them died in about 10 days after the feedings. The survivorship curves of both male and female Aedes (and Culex) mosquitoes fed on the flowers of white clover (Trifolium repens, Leguminosae), stitchwort (Stellaria aquatica, Caryophyllaceae), houttuynia (H. cordata, Saururaceae), a kind of fleabane (Erigeron annuus, Compositae) and shepherd's purse (Capsella Bursa-pastoris, Cruciferae) were almost similar to that of the insects fed on plain water only and almost all died in 8-12 days after the feedings. Among the flowers of 5 woody plants, chestnut tree (Castanea crenata, Fagaceae) was most effective on the longevity of both male and female Aedes mosquitoes, about 80% individuals survived even after 25 days, and the next was Japanese privet (Ligustrum japonicum, Oleaceae), about 60% in males and 70% in females survived after 24 days respectively, and also the insects fed on the flowers of Japanese spindle tree (Euonymus japonica, Celastraceae) survived about 20% individuals after 30 days. In these cases, however, the maximum life-spans could not be seen owing to the shortage of the flowers which must be offered to the insects. Other woody plants, such as Japanese snowflower (Deutzia crenata, Saxifragaceae) and box tree (Buxus microphylla, Buxaceae) were fairly effective on the survival and longevity of Aedes mosquitoes. So it seems to be obvious that the flowers of woody plants including shrubs and arbors are more useful to maintain the insect life than that of the herbaceous plants in general. As a result of the surveys on the sexual differences of the longevities of both Culex and Aedes mosquitoes fed on 5 flowers it was found that male Aedes was longer than male Culex in the mean life-span as well as in the maximum lifespan. This suggests that the male Aedes mosquitoes suck nectar more actively than the male Culex. On the other hand, Aedes mosquitoes had 2 gonotrophic cycles even without any sugar solution but they could repeat 4 cycles under the feeding on 1% or 5% cane sugar solution. This finding suggests that, in natural conditions, adult mosquitoes must take nectar or some sugar containing fluids in order to repeat several gonotrophic cycles.

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