In the previous reports, the authors have studied the stabilization of organophosphorus insecticides and have reported that the surface acidity ofmineral carriers effects the stability of methyl parathion dust formulation with stabilizers, such as polyoxyethylene alkyl ether (PAE), polyoxyethylene dialkyl ether etc. The crop field tests and laboratory experiments were made in order to observe the effect of stabilizers on the insecticidal activity in methy parathion dust formulations. In the laboratory experiment, Callosobruchus chinensis LINNÉ and Allantus luctifer SMITH were used as test insects. In the crop field test, the first and second broods of the rice stem borer, Chilo suppressalis WALKER were used as test insects. Methyl parathion dust formulations with clay, clay plus talc (1:1), clay plus talc (3:1) and stabilizers were used as test insecticides (Tables 1, 2). Stabilizers used were PAE, alkyl naphthalene sulfonic acid salt (ANS), #0 fatty acid, and cuttlefish oil. The results of biological assay were shown in Tables 2, 4, 7 and 8, and these values, when transfered into probit unite and plotted against the time on logarithmic scale, revealed linear regressions in the condition under which the experiment was carried out (Tables 3, 5, 6). In the case of methyl parathion dust formulations with stabilizer, the effect on the insecticidal activity depends upon the sort of mineral carriers and stabilizers. When clay only was used as a diluent, PAE 0.5% as a stabilizer increased rather than obstructed the insecticidal activity of methyl parathion dust formulations. When clay plus talc (1:1) was used as a diluent, cuttle fish oil as a stabilizer obstructed the insecticidal activity and it was inferior to methyl parathion dust formulation without stabilizer. ANS had no connection with any sort of mineral carrier and rarely obstructed the insecticidal activity. Methyl parathion dust formulations with clay plus talc (3:1) were scarcely influenced by stabilizers and the result obtained by Bliss probit method is insignificant. But perhaps, the influence of talc brings about the tendency that dust formulations with PAE are slightly inferior to that with #0 fatty acid on ANS in the insecticidal activity. When talc is used as a diluent, stabilizing effect by compounds of PAE series is not remarkable, as the authors have explained in the previous reports. Though we could not ascertain the relationship between the quantity of stabilizer and insecticidal activity in this test, the result obtained by the crop field test shows, evidently that the insecticidal activity of dust formulations with 0.5% stabilizer is superior to that of dust formulations with 2.0% stabilizer and a proper quantity of stabilizer is approximately 0.5-0.7%. Consequently, in the search of a stabilizer for methyl parathion dust formulation use, we should carry out the biological assay in company with the chemical test of stability, sufficiently to determine the proper quantity of stabilizer, stabilizing effect, and the degree of obstructive action.
In the present paper, the data on the frequency distribution of infested stems per rice hill caused by the rice stem borer, Chilo suppressalis, were used. These data were collected from 41 different rice fields in Western Japan over several years. From these data the relation between the mean number of infested stems per rice hill and the proportion of infested units is obtained as shown in Fig. 1, abscissa showing density of infested stems (λ) and ordinate percentages of infested units (P). This relation opens the way to estimate λ by P. If the frequency distribution of infested stems per unit is fully random, the proportion of infested units (P) is to be expected as follow, P=1-e-λ, where λ is the mean number of infested stems per unit. In practice, P is usually shown somewhat underestimated, because of the departure from random distribution. The “negative binomial” often gives a good fit to the actual distribution of infested stems per unit. Thus, the above equation will be changed as follow, P=1-e-aλb, where a and b are constant. Putting m=aλb, P can be transformed in to m, by using Table 1. Fitness of this equation can be examined by a lineality between logλ and logm. The empirical data well agree with this equation. (Fig. 2) By estimating the paramaters, a and b, the following formula was obtained. P=1-e-0.487λ0.937 Table 1 gives calculated values of λ to different percentages of P. This method is intended to save work, because it is far easier to count the number of infested hills than to count infested stems per hill. Some factors affecting this method are discussed.
The spiders of the citrus orchard has received little attention by any entomologist, though they are important for the Arthropod community of the orchard because of their predatory activities. This paper presents a list of 53 species collected in a citrus orchard near Fukuoka from 1955 to 1956. Among them 35 are webbing species, 18 beingnon-webbing ones. This orchard has not been subjected to pest control since 1945, but has been well managed. All the specimens recorded in this list are preserved in the Entomological Laboratory, Faculty of Agriculture, Kyushu University.
Recently the chemical control of injurious insects became remarkably effective but resistant varieties must be used as the basal practice in agriculture for the purpose of increase in yields of crops. Although the breeders have exerted themselves to originate resistant varieties but excellent results are not obtained so easily, because the factors relating to resistance have to be take out from various compound factors. Most of the main factors related to insect resistance must be hereditery, therefore it is considered that these factors are contained within the seeds of plants. If so, the insect resistance of varieties may be compared with each other by the method which makes insect injure seedlings in the stage before the weaning period. Namely, in this stage the seedlings are depending upon the nutrition of albumen only, but not on fertilizers in soil. In this standing the authors have studied the varietal difference of injury caused by the feeding of rice stem maggot which is known to have remarkable varietal difference. The adults used in this investigation were collected from the field in the beginning of October and then were reared on Agrostis matsumurae HACK. (A. perennans matsum. non TUCK. pro parte.), cereal weed till oviposition. The eggs laid on the surface of said weeds were floated on the water in an experimental dish, with the leaves. After about a week the larvae hatched out and fell into the water. On the other hand, the seedlings of rice plants in the stage before the weaning period were cultured under constant temperature. Thus the artificial parasitisms of the larvae on seedlings were conducted and the seedlings were moved into an incubator of 25°C constant. The survivals and the body length of the larvae were surveyed about 10 days after artificial parasitisms because it was known, from the preliminary test, that the larvae reared on seedlings grew to the 3rd instar after 10 days from artificial parasitism. The results obtained are summarized as follows: 1. There were considerable differences in the survivals of each instar but it was clear that the coincidental tendency in the total survival percent and the percentage of individuals that grew to 2nd and 3rd instar larvae, and the correlation coefficient between these two percentages is 0.9401. 2. There were correlations between the total survival per cent (x) of larvae bred on seedlings and the number of injured panicles per 20 hills (y) of each variety observed in the field, and the correlation coefficients and the regression equations of each varietal group which was grouped by their heading date were r=0.8565 and y=45, 76+1.17x in early maturing varieties, r=0.9975 and y=1.25 x-7.96 in medium maturing varieties, and r=0.7088 and y=4.12+0.62x in late maturing varieties, respectively. 3. The correlation coefficient between the total survival per cent (x) and the mean body length (y) of larvae bred on seedlings was 0.8273 and the regression equation was y=1.250+0.025x, and this equation agreed with 99% probability in any groups of varieties. 4. The close correlation between the mean body length (x) of larvae bred on seedlings and the number of injured panicles per 20 hills (y) of each variety observed in the field was recognized, and the correlation coefficients and the regression equations of each varietal group were r=0.8540 and y=41.89x-7.71 in early maturing varieties, r=0.5284 and y=39.90x-40.58 in medium maturing varieties and r=0.8193 and y=22.16x-19.74 in late maturing varieties, respectively. 5. From the observation on injured features of seedlings, the clear border of eating marks were recognized in the varieties on which larvae showed good growth