Insecticidal activities of 50 substituted phenyl N-methylcarbamates were evaluated with the smaller brown planthopper, and the green rice leafhopper by several testing methods. As preliminary tests, direct, residual, and systemic effects of these compounds against both insects were valued on rice seedlings treated with them. Among these compounds, phenyl N-methylcarbamates substituted with 2-OCH₃, 3-OCH₃, 2-OCH(CH₃)₂, 3, 5-di-CH₃, 3, 4-di-CH₃, and 2-Cl-3, 5-di-CH₃ showed high insecticidal activities against both insects. Based on the results of preliminary tests, effects of five compounds against both insects were evaluated by spraying on leaves and by application into the water in the Wagner's pot in which rice plants were cultivated. Of these, 2-chloro-3, 5-dimethylphenyl N-methylcarbamate showed higher insecticidal activities and longer residual effects than the others. The insecticidal activities of 3, 5-dimethylphenyl N-methylcarbamate appeared very rapidly when applied into pot water, but its residual effects were inferior to that of 2-chloro-3, 5-dimethylphenyl N-methylcarbamate.

View full abstract

Under a long day condition a linear relation between temperature and developmental velocity in both species, Agrotis ipsilon and Agrotis fucosa, was observed at 15∼30°C in the egg stage and at 20∼30°C in the larval stage. The calculated threshold of development and the thermal constant of the egg and larval stages in the two species was 11.3°C, 56.5 day degrees and 5.6°C, 387.3 day degrees in A. ipsilon and 11.0°C, 78.7 day degrees and 4.2°C, 589.0 day degrees in A. fucosa respectively. The threshold of development in both stages was hardly different in the two species, but there is a remarkable difference in the developmental duration between these two species, especially with increasing temperature. The larval development was more or less retarded under short day condition in A. fucosa, whereas in A. ipsilon no such tendency was observable not only under short but also long day condition. From the results it may be suggested that in A. fucosa the larval diapause was induced by photoperiodic condition.

View full abstract

It has already been shown that the flight form of the southern cowpea weevil, Callosobruchus maculatus, is induced by the rearing conditions during the larval stage, such as larval crowding and high temperature. In the present work, it was experimentally proved that the photoperiod is also one of the factors that induce the flight form. The flight form emerged in a high percentage under two extreme photoperiodic conditions, namely 24 hours light and 24 hours of darkness, and the flight form decreased gradually in its percentage with the change of the photoperiod to the intermediate zone, at which time the emergence of the flight form was almost zero percent. This photoperiodic reaction is illustrated by a U-shaped curve, which is rather different from the types known from published literature. It is also assumed from the results obtained that the appearance of the flight form in high frequencies at the dark side of the photoperiod may have a significant role in the adaptation of the insect to the stored condition of bean or cereal products.

View full abstract

The insecticide treatment period for the effective control of the Japanese wax scale, Ceroplastes japonicus GREEN was examined. The authors conducted observations on the seasonal occurrences of crowlers, their age distribution, successional changes, and the growth rates of the different larval stages and also examined the controlling effect possessed by two kinds of insecticides upon some of the developmental stages of this scale insect. The crowlers occured most abundantly in June. Its peak occurrence was found to be in the middle and late June. The growth rates of the larval stages were observed to be as follows: 1st instar ranged from 20∼34 days, 2nd instar ranged from 30∼40 days and the 3rd instar ranged from 40∼54 days. Two kinds of insecticides viz. Imidan and Fussol were treated upon 6 developmental stages, from late 1st instar stage to late 3rd instar larvae. As results, it was observed that Imidan was effective in the beginning of 2nd instar and Fussol was most effective from the late 2nd instar. From the results of this experiment it is concluded that an adequate time for control by Imidan was 25∼30 days after the first emergence of crowlers, and by Fussol about 50 days after the first emergence of crowlers.

View full abstract

Toxicity of several organophosphorous, carbamate, and chlorinated hydrocarbon insecticides on three species of planthoppers on rice plants was determined by the micro-topical application method. The insects tested were the adults of the brown planthopper, Nilaparvata lugens (STÅL), the white-backed planthopper, Sogatella furcifera (HORVATH), and the smaller brown planthopper, Laodelphax striatellus (FALLÉN). Insecticides were applied by means of an applicator that consisted of a screw micrometer and an ultra microsyringe used for injecting the samples in gaschromatographic analysis. This device enabled the quick application of as small as 0.05μl solution of insecticide dissolved in acetone to the thoracic regions of the test insects. Treated insects were placed at 25°C, and the mortality counts were taken at 24 hours after treatment. Comparison of LD₅₀'s indicated as follows: (1) The organophosphorous insecticides tested are the most selective insecticides showing much lower toxicity to the brown planthopper than to the white-backed planthopper and the smaller brown planthopper, and they are slightly less toxic to the white-backed planthopper than to the smaller brown planthopper. (2) The carbamate insecticides are the most toxic group of the compounds tested. They are almost equal in toxicity to the three species of the planthoppers with the exception of several which show relatively lower toxicity to the smaller brown planthopper. (3) The chlorinated hydrocarbon insecticides are less toxic than the organophosphorous and the carbamate insecticides, and their toxicity are not selective. (4) There is no significant difference in the susceptibility between males and famales.

View full abstract

Excretion of honeydew by a scale insect, Ceroplastes pseudoceriferus GREEN, reared on pumpkin fruit, was kept under observation during its growth and development. Frequency of excretion of honeydew-droplets rapidly decreased through the larval stages. On the other hand, the amount of a droplet of honeydew per insect weight remained constant throughout development. The feeding activity of this scale insect was therefore assumed to be high in the early larval stages. Diurnal rhythm of honeydew excretion was particularly remarkable in the younger stage. The maximum and minimum frequency of excretion were observed between 18:00-20:00 hours and 6:00-8:00 hours, respectively. Field experiments were carried out to examine the effects of several insecticides on the scale insect, C. pseudoceriferus, and an aphid, Myzus persicae SULZER. Number of honeydew-droplets detected on a paper sheet of a definite size was successfully employed as a criterion for the evaluation of insecticides on these insects.

View full abstract