Three Japanese species of the Genus Ceuthorrhynchus injurious to the Cruciferous plants are treated in this paper. Studies were made at Fukuoka City in 1955. 1. Adults of the three species are separable by the following key : 1(2) Antennal f unicle 6-jointed, the intervals of striae flat. Derm black or brownish black, legs brown. Underside, lateral margin of prothorax, scutellal spot and the first interval closely covered with white feathery scales, residual portion moderately covered with grey hairy scales. Length : 2-2.5 mm......................Ceuthorrhynchus albosuturalis (Roelofs) 2(1) Antennal funicle 7-jointed. 3(4) Derm black, elytra dark blue, scutellal spot absent. Scales very minute, dark brown. Pygidium strongly impressed. Length : 2.5-3 mm................ Ceuthorrhynchus ibukianu. s Hustache 4(3) Derm and elytra black. Prothorax clothed with grey hairy scales, before and behind the scutellum with distinct spots composed of white feathery scales, intervals of striae clothed with 2-lined white hairy scales. Claw toothed. Length : 2 mm...........................................Ceuthorrhynchus sp. 2. (a) Annual life history of C. albosuturalis. The overwintered adult beetles appear and visit the flowers of Capsella bursa-postoris or sprouts of Nasturtium indicum from the middle of March. After copulation the female makes a hole in the pod wall with its beak and then turns backwards to place an egg into the pod. Oviposition is very active in the first half of April. Eggs are 0.486±0.005 x 0.290±0.007 mm in size. Larvae moult twice (Table 1, Figure 1), larva and pupa are as shown in Plate 8. Mature larvae fall to ground, bore into earth and make pupal chambers of which the wall is pasted internally with their viscous secretion. When immature larvae compelled to fall owing to the snapping of ripe pods, they also creep into earth, but are unable to complete the pupal chambers or unable to pupate even if they could complete major chambers. The duration of each developmental period is : 5-6 days for the eggs at the end of April, 5-6 days for the first stage larvae and 5-8 days for the second at the beginning of May, about 10 days for the third at the middle of May, 5 days for prepupal stage, and 5 days for the pupae. Newly emerged adults are easily distinguished by the coloration of scales which are more or less brownish ; the feathery scales are faded in white and hairy ones in dark grey after several days. From the middle of May new adults appear and feed rather voraciously, but gradually disappear by the end of June. The periodical changes of the food plants are as shown in Figure 2. Rape is cultivated as a cource of oil. Cabbage, turnip, radish and chinese cabbage are winter crops and only the remainder after harvest of them are attacked by the pest. Whether the females deposit eggs into the seedpods of Nasturtium indicum has not been ascertained. (.b) The injury infested by C. albosuturalis. Seedpods of the cruciferous plants are injured slightly by the overwintered adults, which bore into pods to eat the seeds or to oviposit, more severely by the larvae which live on the seeds in the pods, and slightly by the newly emerged adults. Seedpods of the wild rape may be divided into four stages according to the state of the seeds, and the degree of injuries are compared among those stages. Materials were collected at Hikosan on May 16. Results are as shown in Table 2, Figures 4 and 5. The injury to the rape (Nurin no. 17) was examined at the Kyushu University Farm from May 21 to 24, results are as shown in Table 3. Total percentage of injury is 1.15 % in seed number. 3. C. ibukianus lives on Nasturtium indicum from April to May. 4. Undetermined species of Ceuthorrhynchus lives on Cardamine flexuosa, the life form is similar to that of C. albosuturalis. Eggs, 0.69 x 0.38 mm in size, are deposited near the tip of seedpods, larvae feed on seeds toward the base of pods. The larvae fall onto the ground by three different reasons, i. e. the first case is that the mature larvae leave the pods in order to pupaite in the earth, the second is that the larvae are' compelled to fall by the snapping of the ripe pods, and the third is that the larvae are obliged to leave the pods after eating up all the seeds in the pods. So that the body length of the fallen larvae are various. An injured pod is diagrammatically shown in Figure 3.