Some ecological surveys and experiments on Culex tritaeniorhynchus GILES were carried out with 406 strain and wild-caught mosquitoes. The former strain has been established in the 406th Medical General Laboratory U.S. Army, Atsugi, Japan and the latter was collected with a light trap at a pigpen in the suburb of Yokohama. The average number of eggs per raft collected from July to September 1966 was 207.2 eggs, while 406 strain, when fed on mice, laid 172.3 eggs which was significantly less than the former. However, the hatching rates of egg batches of both groups were same, being 94% in fifty rafts counted. In a test using 406 strain mosquitoes, the number of eggs per raft decreased at the rate of about 15% in each gonotrophic cycle, namely 174.1, 148.9 and 126.7 eggs per raft for three successive cycles respectively. In the rearing cabinet (27°C, RH 80%), some of the females of 406 strain mosquitoes were able to repeat four gonotrophic cycles for about 25 days. The parous rates of the wild mosquitoes were checked from April to October in 1966. It was 16.2% in April and 10.6% in May and these were the lowest throughout the season. In June, July and August the parous individuals increased more than those in the previous two months and the rates were calculated as 31.0%, 35.4%, and 32.9%, respectively. From September to October, the wild female population became rapidly older as compared with the preceding months, being the parous rates 57.7% and 92.8% respectively. By age-grouping method, the parous mosquitoes from the field were found to have either one, two or three relics and among them uniparous females accounted for 94.9% of all parous ones. However, it is very probable that there were more biparous or triparous females, since many engorged individuals were usually found in the parous female populations. From these results, it was suggested that the hibernating adult females should be developed since early September and most of them did not fly to the host-sheds but migrated toward other hiding places to hibernate, although some of the female adults which engorged and laid egg-rafts during September and October would also possibly survive until the following spring, especially in the south of Japan.

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Food-plants of the family Tenthredinidae so far known at present were listed herein, continued from the previous paper. The plants observed by the author or reliably recorded were given in scientific names, and the plants for new records were shown with an asterisk. The synonym concerring three species were newly arranged.

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Afferent impulses from the contact chemoreceptors were observed following the direct contact application of DDT to the tip of the chemosensory hairs on the maxilla of silkworm larva. No chemosensory neurons were activated directly by DDT itself. Pretreatment with relatively low concentration of DDT increased the frequency of impulse discharges evoked by chemical stimulation, indicating increased sensitivity to the chemical. At the concentrations of DDT higher than a certain critical level, trains of impulses which are characteristic of nervous symptoms of DDT poisoning appeared in place of single spikes after a certain latent period (about 2min.). At much higher concetrations, the amplitude of the train of impulses extremely decreased and finally the response disappeared. In rare cases increased negative after-potential was recorded. A small difference in susceptibility to DDT was observed among the maxillary chemoreceptors. The chemoreceptors were more susceptible to DDT at lower temperatures than higher temperatures. When an appearance of trains of impulses in the inositol receptor was taken as a criterion of the symptom of DDT poisoning, there was a small difference in susceptibility to DDT among about 30 silkworm strains tested. However, no correlation was found between the susceptibility of the receptor shown by ED₅₀ and the torelance of whole-larvae shown by LD₅₀ per body weight which was obtained in the topical application test.

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The author made observations on the distribution of larvae and pupae of Pieris rapae crucivora, Mamestra brassicae and Autographa nigrisigna on each individual plant of cabbage. Young larvae of all the three species distributed mainly on the underside of leaves of intermediate ages. Characteristic distribution for each species was observed after middle instars of larvae: Pieris larvae a migrated toward the upper side of young leaves with their growth and went back again toward the underside of leaves of lower part before pupation. Mamestra larvae showed a migrating tendency toward the upper young leaves with the progress of age and always stayed on the underside of leaves. Almost all of the fifth and sixth (last)-instar larvae aggregated at the head of the plants, whereas full-grown larvae went down into the soil for pupation. Autographa maintained a sessile habit throughout the larval life, so the later instar larvae and also the pupae were found on the underside of old leaves of lower part. Tht effect of larval density on the vertical distribution was observed only in Mamestra; the aggregating tendency of the later instar larvae was accelerated by the increase of density. Each species distributed on the plant irrespective of the existence of other species and also of the seasons.

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The determination of larval instars of leaf mining flies has been made on the basis of the size of their pharyngeal sclerites or spiracular processes hitherto. However, these methods proved very disadvantageous on account of their requiring much inconvenient labor for measuring the size of these organs. Some other biological characteristics in Phytomyza ranunculi larvae were investigated in order to find a simpler method for larval instar determination of leaf mining flies. The body length, the width of mine and the size of frass which now can be measured much easier, were found to be distributed normally in each instar which had been determined on the basis of size of pharyngeal sclerites. From the result of these normal distributions, a median between each of average values of each of the characteristics of two adjacent instars was applied as a limit value of discrimination of those larval instars. The body length or the mine width was comparatively better criterion respectively with the probabilities of less than 20% of misclassification in each instar, while the frass size was out of criterion with the probabilities of higher than 35% in maximum. So there can be no difficulty in adopting each of the former two characteristics respectively as criterion for instar determination with conditions attached of misclassification probabilities above-mentioned. Further, a comprehensive determination of larval instars was attempted with the discriminant function, in which the mine width and frass size were used as two variables. The median between average values of discrimination of two adjacent instars was adopted as a limit value of discrimination of instars. The efficiency in this method was rather better than that in the above one with the mine width only. The probability less than 10% of misclassification was gained in this method when the body length was used as one of two variables instead of the frass size. The discriminant function seems to be more useful for determination of larval instars when adequate characteristics are adopted as it's variables.

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The larvae of the rice stem borer, Chilo suppressalis WALKER, were reared on several artificial diets of different compositions under diapause-inducing condition (25°C and 12hr photoperiod). After 60 days of aseptic rearing, the larvae were kept at 8°C for 60 days, then they were incubated at 25°C for pupation. When the larvae were reared on diets containing rice bran or rice germ seedlings, most of the larvae survived after low temperature treatment. On the other hand, if the larvae were reared on four other kinds of diets which lack in plant materials above-mentioned, 80% of larvae died during the course of low temperature treatment. The larval blood proteins are divided into three main protein bands by agar gel electrophoresis technique; that is, albumin and globulin bands moving to anode side and another globulin band moving to cathode side. Of these bands, the globulin band moving to cathode side was more clearly detected in the diapausing larvae which were reared on suitable diet than that of the larvae reared on unsuitable diet. Accordingly, the inspection of protein fractions of haemolymph by means of an electrophoresis technique seems to be very useful to approach nutritional studies in insects.

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Based on the fact that nereistoxin, a toxin isolated from a marine annelid, Lumbriconereis heteropoda, has insecticidal action, the studies for developing derivatives of the toxin as insecticides have been conducted in our division. In the present paper, the insecticidal activity of one of the derivatives, 1, 3-bis (carbamoylthio)-2-(N, N)-dime-thylamino) propane including its hydrochloride (cartap, Padan^®) was reported. By the screening tests, the compounds were proved to be toxic against lepidopterous larvae such as the rice stem borer, the army worm and the cabbage worm. The compounds were toxic also against the soy bean aphid, the 28-spotted lady beetle and the green rice leafhopper. For the adult house fly, by the injection the compounds were revealed to be toxic, but by the topical application were not effective. Tetranichid mite, Tetranychus kanzawai was tolerant to the compounds. In a spray test on the rice stem borer being in rice plants in pots, the soluble powder and the dust formulations of the compounds were compared with organophosphate insecticides in the effectiveness for controlling the larvae. The spray of 0.025% solution, and dusts of 1% and 2% of the compounds were almost completely effective to depress the larval population in the stems. In the residual action to prevent the larval boring, cartap was found to be superior to its free base, Sumithion, Lebaycid and Phenthoate, but somewhat inferior to EPN. The fact that the solution of cartap applied on the surface of the rice leaf-sheath killed the larvae in the stem apparently indicates the penetration of the compound into the stem. Cartap showed the stability to the rainfall and the sunlight on the rice plant. Topical application tests on the rice stem borer larvae collected in several districts in Japan showed no local difference in the tolerance to the toxicity of cartap. The spray of 0.05% solution of cartap was highly effective in controlling the damage to citrus trees by the citrus leaf miner in a field test. The toxicity (oral LD-50, mg/kg) of cartap was 165 to the mouse and 250 to the rat. The toxicity (MLC, ppm) to the killifish and the carp was 0.4 and 1.5 respectively. The present data afford promise of practical use of cartap for control of pest insects.

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The possibility of practical use of cartap (1, 3-bis (carbamoylthio)-2-(N, N-dimethylamino) propane hydrochloride) mixed with DCPA (3, 4-dichloropropionanilide) was investigated with some experiments to determine the insecticidal and herbicidal activities, including phytotoxicity, of the mixture. The effectiveness of cartap for controlling the larvae of rice stem borer being in the rice stem was not influenced by mixing with DCPA. In the bioassay by dry-film method with azuki been weevils, Callosobrnchus chinensis L., the significant difference in toxicity of cartap was not observed between the simultaneous application of cartap with DCPA and the application cartap only. The young plants of barnyardgrass was killed completely by the foliage spray of DCPA, while its herbicidal activity was not impaired by the presence of cartap. These results showed apparently that cartap or DCPA acts independently without any interactions between them against both insects and herbs. The significant phytotoxicity of DCPA treatment with cartap against the seedlings or the transplanted rice plants was not observed. However, DCPA with organic phosphorus insecticides was highly phytotoxic causing complete death. Cartap did not inhibit the DCPA-degrading enzyme in rice plants in vitro, while organic phosphorus insecticides inhibited this enzyme. Non-phytotoxicity of DCPA with cartap, therefore, might be based upon non-inhibition of the DCPA-degrading enzyme by cartap. The results seem to endorse the practical advantages of the combining cartap with DCPA to control the pest insect and the herb of rice plant.

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[in Japanese]

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