1. Population censuses on the wireworm, Melanotus caudex LEWIS, which were limited to the individuals larger than the 2nd-year old, were taken in spring on barley field and in autumn on Chinese cabbage field in 1957.<br>2. The distribution pattern of the individuals in each section and that beside each plant root in both seasons were in accord with the frequency distribution of Pólya Eggenberger type. χ² test of the fitness was better in the case of plant root than that on the section.<br>3. To estimate the wireworm population, the counting on the number of worms living beside a plant root is more convenient, because the worms living in a section outside a root of Chinese cabbage are fewer than those living beside a plant root.<br>4. The explanation of the concentrating nature of the distribution pattern of the wireworm is as follows;<br>a) the oviposition of the adult insect takes place individually in the soil surrounding the crop plant;<br>b) the wireworm living near to the soil surface feeds on the crop plant and creeps into it; and<br>c) the wireworm dwells just under the plant, when it creeps into the deeper layer of top soil.<br>5. Among the factors opposing the concentrationof the wireworm to crop plant, the scattering of concentrated worms due to soil preparation for wheat (in autumn) and sweet potato (in spring) was taken into consideration. But it did not have a great influence on the dispersion of the wireworm larger than 2nd-year old for the disturbance of soil surface occurred after the wireworm sank into the deeper layer of top soil.<br>As a natural enemy of the wireworm, a species of Bethylidae was collected. It has any great influence on the distribution of the worm.<br>6. The frequency distribution in the barley field showed almost the same tendency as in the field of Chinese cabbage.<br>7. The farms tested had gentle slopes, the west side was higher than the east. Consequently, the density of wireworm was higher at lower side than at the other. It may be due to the special climatic condition at the lower side where no wind blows and it is sunny.<br>8. In order to find the relations between the difference of population densities and the degree of aggregation of wireworms, the value, S²/x, of each field-section was compared. The values of S²/x proved to be above one, and the degree of aggregation became higher as the density of wireworms increased. The frequency distribution in each section agrees well with that of Pólya Eggberger type, and this fitness is better as the density of a section increases.<br>9. The number cf wireworm living besides the <br>root of Chinese cabbage was examined. The <br>number of collected worms shows the maximum <br>in the damaged and undamaged leaves in mixed <br>growth, and decreases at the withered root, the <br>undamaged root, and the root-lacking place.<br>10. The value of S²/x at the root-lacking place is below one, shcwing no aggregation of the worm. This comes from the fact that the worms moved to other plants from the Chinese cabbage, which withered due to the damage. The comparatively high aggregation was seen at the undamaged roots.<br>11. The wireworm density was comparatively low near an ant nest or a mole-hill. At the place of its high density, the only a few larvae of soy bean beetle could be collected, while a few more were collected at the farm-border.<br>12. When the larvae of the soy bean beetle and the wireworm gather near the plant root on the farm where few plants grow, the former was frequently killed by the latter.<br>13. It was observed that wireworm fed on the larva of the say bean beetle in a field. The same was observed when wireworms and the larvae of the soy bean beetles were bred in the same pot.