In this paper some problems concerning the phytotoxicity caused by bark treatment or painting of methyl demeton (metasystox) were discussed based on the authors' experiments practiced chiefly on citrus trees. The results obtained are summarized as follows.
1. The bark injury in citrus trees was more remarkable than in other fruit trees (Fig. 1). In such damaged branches death of cambium and development of callus were recognized by anatomical studies (Fig. 4).
2. The degree of Phytotoxicity of various chemicals was ranked as follows according to field experiments and anatomical studies.
thiol-metasystox (96%), thiono-metasystox (94%)≥metasystox (50%)>metasystox-i (25%)
Injurious action of the solvent and emulsifier of the insecticide were negligible so far as a normal painting was concerned.
3. Thickness of the insecticide painted on bark is an important matter in view of phytotoxicity, especially in citrus trees. It may be said the upper limit of safe thickness of metasystox-i (25%) in bark treatment, not diluted, is about 0.6cc/100cm² in citrus trees.
4. A close correlation between bark injury and high temperature was affirmed through many experiments of citrus trees. In laboratory experiments the influence of high temperature appeared more remarkably when test plants were exposed in the air condition soon after the insecticide treatment.

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The present experiment was carried out in order to investigate the relationship between the life-cycle of green rice leafhopper and rice yellow dwarf occurring in a large scale.
The results obtained are summarized as follows;
1. The adult of the overwintering generation begins to emerge out from the 2nd decade of February to the 1st decade of March, and almost all of the imagoes become adults in the beginning of April. The population of these adults decreased rapidly from the middle of May, but some individuals survived until the end of May.
2. The population density in spring counted by sweeping did not coincide with the number of individuals caught in light trap. First and 2nd decades of April when the population of imagoes become to minimum seems to the end of emergence.
3. As the result of rearing test from winter to mid-summer, imagoes appear till the 1st decade of April in the first generation, and start to emerge from the 2nd decade of May and survive till the 1st decade of July. The second generation adults appear from the beginning of July till middle of August, and the third generation continues.
4. The relation between the life-cycle of leafhopper and the growth of rice plant is that the damage from overwintering and the first generations is heavy in case of early cultivated rice plant, and the second generation adults increase in number at harvesting time. Rice seed of normal cultivation will be sown about at the end of overintering adult stage, and that of late cultivation at the end of first generation in adult stage.
5. Diseased plants are recognized at the end of June about 70 days after virus is transmitted into early cultivated rice plant by overwintering hoppers. The latent period of the virus in the hopper taken from diseased plant was from 21 to 28 days. These hoppers, therefore, will become able to transmit virus about at the end of July.
6. Some adults at the beginning of April and at the end of July are recognized as virus vectors, but imagoes from the middle to end of May and adults from the middle of June to the middle of July, i.e., leafhoppers of the first generation and early period of the second generation have no virus.
7. Infection period of yellow dwarf virus to the early cultivated rice plant continues from the middle of May. However, it becomes non-infectious until the end of July. No symptom of yellow dwarf is observed on the early cultivated rice plant infected twice while it is growing, appears on young shoot from the rice stubble.
8. The wild plant, Alopeculus auqualis SOBOL was examined in spring but was found not infected.
9. The overwintering generation of leafhopper is most important as the vector of the yellow dwarf virus as the primary infection in the paddy field. It is considered that the generations from the 2nd are chiefly transmitting virus from these diseased early rice plants.

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The predaceous insects and spiders in apple and pea orchards play together an important role in the natural control of arthropod pests. Among them, coccinellids and various kinds of spiders feed particularly on the pear aphid and apple leaf-curling aphid until the phytophagous mite attack the fruit trees. Considering this point, any soundly devised pest control schedule on orchard crops should be taken under the consideration of the advantage of natural control. Following the preceding test, to attain the above mentioned purpose, an attempt was made to evaluate the daily feeding ability of five predators, and further, limited test was taken on the effects of some pesticides commonly applied in the orchard area onthe predator population in the laboratory.
Both the adult coccinellids, Coccinella setempunctata bruckii and Harmonia axyridis, fed on about 38 aphids per day per individual, and it proved to be the most effective among the predators tested. While in average daily consumption of the other adult species, Propyraea japonica ate about 18 aphids, and similarly Misumena tricuspidata consumed in average 15 or so per day. But in marked contrast with the above amount of consumption, only one or one decimal five in average number of the alate or apterous aphids were eaten by adult Theridion octomaculatum per day.
In the further experiments on the toxic effect of some pesticides upon the useful predators, it was suggested that malathion appears to be quite clearly harmful in marked reduction of predator populations. Lead arsenate and glyodin, on the other hand, are only slightly toxic or innocuous to them. It can thus probably be said that the decrease of predators in crop fields by the application of potenticial insecticides may cause aphids to be set up the point of economical importance.

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During the course of nutritional studies on the rice stem borer, Chilo suppressalis, it was found that the rice plant contains certain factors which inhibit the growth and development of larvae. Extraction and isolation of these factors from the rice plant and feeding tests with larvae on synthetic food media under aseptic conditions, were undertaken in order to characterize them. The results obtained were as follows.
1) The rice plant contains certain growth inhibiting substances against rice stem borer larvae, even though the rice plant is the principal host plant of the insect.
2) Factors having high potencies were extractable with ether from water-extract of rice plants. The growth inhibiting activity was found in several fractions of the ether extract, showing that there are many factors responsible to the growth inhibition of the larvae. Among the fractions of the ether-extract, neutral and basic substances showed higher potency than acidic substances.
3) From the acidic fraction, benzoic and salicylic acids were detected. Occurrence of benzoic and salicylic acids in the rice plant has hitherto not been recorded.
4) The growth of larvae was clearly inhibited by adding benzoic or salicylic acid to their food medium at a concentration of about 1.4 per cent on dry weight basis. Many of the larvae could not grow and died on a food medium containing more than about 3 per cent of these acids.
5) Benzoic and salicylic acids have also inhibiting effects on spore-germination of the rice blast fungus, Piricularia oryzae, and the brown spot fungus, Cochliobolus miyabeanus. Spores of both species could not germinate at a concentration of 0.1 per cent of the acids; and even with 0.01 per cent of salicylic acid, spores of the latter species were unable to germinate.

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[in Japanese]

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The sensitivity of the central nervous system to the direct action of DDT was compared among three strains of houseflies. The threshold concentration of DDT for inducing motor discharges of impulses in the leg was taken as a measure of nerve sensitivity. It was found that there is a close parallelism between mortality and nerve sensitivity; nerve sensitivity is highest in the highly susceptible strain, itis moderate in the moderately susceptible strain, and it is lowest in the resistant strain. It is concluded that the nerve sensitivity to DDT plays an important role in resistance.

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