During the past several years malathion has been applied in controlling the small brown planthopper, Laodelphax striatellus FALLÉN, in Hiroshima Prefecture. In early summer of 1964 a number of rice growers experienced difficulty in the control of small brown planthopper by helicopter application of malathion in some parts of the middle and northern areas in Hiroshima Prefecture, while excellent controls were given in another areas.
Because of failures of control in malathion applications in 1964, this study was undertaken to determine if malathion resistance in this planthopper had developed. The test insects were collected from 21 localities of Hiroshima Prefecture and in 6 localities of other prefectures, and they were treated by root treatment with malathion.
The results obtained in this study are summarized as follows.
1) The planthoppers from many areas varied markedly in their responses to malathion with different localities of insects. For instance, in Nagano colony (Osaka Prefecture) which showed the highest susceptibility to malathion of all colonies, the LD-50 values (μg/tube) of adult female and male were 53.4 and 33.0 respectively. That of adult male of Chiyoda colony (Hiroshima Prefecture) which were lowest of all were 343.1 and 315.7 respectively. In adult of Chiyoda colony, the level of malathion resistance was 6.4- to 9.6- fold to Nagano colony at the LD-50. All colonies from 27 localities were grouped into three orders according to the degree of malathion resistance. Resistance was shown by colonies from Chiyoda, Toyohira and Saijo. Some susceptibility was indicated in 6 colonies from Hiroshima Prefecture, (2 colonies), Yamaguchi (2), Osaka (1), and Hokkaido (1).
2) In Hiroshima Prefecture, malathion resistant planthoppers were found throughout the whole region and the degree of malathion resistance varied markedly in each area. It seemed that there were no relations between the variations in the resistance to malathion and the distance of the locations of collection, and that resistance to malathion developed at each locality itself, even in the case of the small brown planthopper which goes through extensive migration or flight.
3) The standard deviation of susceptibility to malathion in each colony was correlated with the LD-84 value. Therefore, the increase of resistance in the small brown planthopper induced non-uniformity in its reaction to malathion.
4) Considerably the high correlation was recognized (r=0.693) between the LD-50 value and the amount of malathion used in the past nine years at the areas where the test insects were collected.
It is now evident that the repeated application of malathion was one of the contributing factors to the development of malathion resistance.

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As the oral infection formula is considered as supergeometric function, it may be assumed that the infection of pébrine disease may progressively increase in accordance with increasing number of larvae per silkworm tray, even though the percentage of diseased larvae remains as in the beginning. Infection experiment using a number of newly hatched larvae per tray, 5, 000 and 20, 000 each justifies the above consideration.
The increasing grade of diseased moths, however, is not so conspicuous as expected. Its cause is derived from elimination of diseased larvae and from the fact that almost all of them are spread by larvae orally infected with spores during the 4th and the 5th stages having the same number per tray.
Percentage of diseased moths derived from newly hatched larvae that are lightly infected is exceedingly greater than that of moths derived from the heavily infected. For, the former can be alive long, consequently becomes the source producing more diseased larvae which can discharge much faeces containing spores during the 5th stage, that are most liable to be infected with pébrine among the whole stages.

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The present report dealt with the effect of environmental temperature on radiation induced male sterility in the silkworm Bombyx mori. Evidence has been obtained that sterility induced by irradiation has been influenced to a great extent by the difference of temperature after irradiation whereas no significant effect was indicated when the temperature treatment was given before irradiation. Furthermore, it was revealed that the duration necessary for the effectiveness of the post irradiation temperature to be clearly apparent was about 48hrs after irradiation resulting in the highest percentage of unfertilized eggs at the high temperature (30°C), followed by those at moderate (24°C) and last by the low temperature (18°C) at which the pronounced decrease of unfertilized eggs was observed. In cytological analysis, spermatogonia were found to be most sensitive to radiation and were readily destroyed shortly after exposure. However, the radiation induced sterility in this insect was determined by the fate of spermatocytes at the time of exposure. Almost all the spermatocytes were very changeable according to environmental temperatures of post irradiation, these being death, or functionless abnormal spermatozoa at high temperature or functional normal eupyrene spermatozoa in the case of low temperature treatment. Thus the effectiveness of post irradiation temperature is manifested on the fertility of the irradiated males.

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Male azuki bean weevils sterilized by apholate topically applied in acetone were as competitive as normal males in mating. Total number of eggs deposited in every combination of sterilized and normal males for females were equal within the random sampling error in every level of dosage applied. Total number of eggs hatched were decreased according to the increase of the number of sterilized males in the sterilized and normal male combinations. Percentage of eggs hatched was inversely related to the dosage.

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The salivary secretions of leafhoppers are considerably important for their toxic effect on the host plant, and concerning the transmission of plant viruses. In the present paper morphological and histological studies were made on the salivary glands of the rice plant leafhoppers in order to help to throw light on their functions. Results obtained were summarized as follows: -
(1) The salivary glands were consisted of a pair of principal gland and accessory gland, and their conducting parts. In N. cincticeps and I. dorsalis, the principal gland was a compact mass made up of six kinds of secretory cells, and bilobed. It was characterized by the much smaller anterior lobe and the six large III-cells of the posterior lobe. The accessory gland was extremely short and bent tubular gland. In L. striatellus, S. furcifera and N. lugens, the principal gland was an aggregate body consisted of eight kinds of follicle that were made up of a small number of secretory cell. The accessory gland was a bi-cellular gland being somewhat constricted spherical in shape.
(2) With histological staining it was demonstrated that each kind of secretory cells in N. cincticeps and follicle of L. striatellus had distinctly different cytological structures suggesting their different functions (Text-Figs. 2 and 4; Tables 1 and 2). It was considered at least that the IV-cells of N. cincticeps and the A-follicle of L. striatellus produced digestive enzymes, and that the V-cells of N. cincticeps served as one of the sources of the sheath material.
(3) In N. cincticeps the accessory gland was divided into two portions, the head and tail portions. The tail portion was resembled in structure to the Malpighian tubules, and it was hypothetically assumed that this portion absorbed selectively certain non-protein solutes from hemolymph. In L. striatellus the accessory gland was regarded as a main source of the sheath material.
(4) Both the principal as well as the salivary ducts seemed to perform some function other than a mechanical transport of the secretions.

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Investigations were conducted during 1961-1965 on the dispersal of Nezara viridula in relation to feeding and oviposition. Adults of the hibernant generation feed and mate on the fields of rape, radish, wheat and barley, and then gravid females disperse to other kinds of host plants, e.g. potato, beans etc. for oviposition. This was supported by the low sex ratio observed on food plants after passing the date of 50 per cent mating.
During the early census period, the population density of adults in the potato field was very low and most of them were composed of females. Almost all the egg-masses were also deposited in this period. In addition, the mean duration of stay of these egg-laying females was considerably short in comparison with that of the adult migrants in the late period. It was considered that females of which ovaries had matured on the food plants flew into the potato field for oviposition and returned to the food plants soon after oviposition. Many adults of both sexes flew into the potato field in the late period principally for feeding and mating. The fact that an early stage of the host plant was availed by gravid females as an oviposition site and the same plant was accepted for feeding as it grew was maintained not only for potato but for paddy as well.
As stated above, it should be realized that what is meant by a polyphagous habit is not the non-selective preference to various host plants, but involves the sensitive preference to a particular host in an ideal state for the insect. In the study of polyphagous insects it is not only necessary to list many host plants available, but also to assess these host plants in relation to the life cycle and the behavior of the insect.

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The sporulation of germanus ambrosia fungus was investigated in relation to the environmental conditions. The results obtained are summarized as follows.
The ambrosia fungus proved essential for the propagation of ambrosia beetles.
1. Optimum temperature range for sporulation of cultivated spores (type A) on a yeast extract-glucose-peptone-agar medium was from 20°C to 25°C. It was so narrow that the growth of the beetle was indirectly limited by the soil temperature under natural condition.
2. Sporulation of stored spores (type B) was observed only shaking culture with yeast extract-glucose-peptone medium at 20°C and 26°∼30°C. Stored spores were usually found in a mycangia of beetle throughout the year, although the existance of type B spores in the mycangia during the winter was not clear.

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