Living adults or beans infested by the weevil, Callosobruchus chinensis, were collected at different localities in the northern area of its distribution, (Fig. 1,Table 1). The weevils collected from the field were reared at one pair and 32 pairs per 10gr. of the beans generated under the conditions of 30℃, 75% R.H., and illumination of 16hr. photoperiod. The activity of the adult was measured by flight intensity stimulated by light, using the apparatus devised by NAKAMURA (1966), and two types, active and sluggish, were grouped separately. Among all local C. chinensis examined there was no remarkable difference regarding the duration of the preimaginal period at the constant temperature of 20,25,27.5,30℃ and humidity of 75% R.H., the number of eggs per female of the active type, the effect of the larval density on the percentage of the emergence of sluggish type, and the relation of the number of eggs laid to the value of Is, in the distribution of eggs laid per bean (Table 2,Fig. 2,3,4). Conspicuous differences among them were however, found in the adult activity, and the number of eggs per female in the sluggish type. It was not clear whether the number of eggs per female in the sluggish type tended to increase from the southern to the northern localities (Fig. 5). However, we can say that the increase of the population density over a certain level may be necessary to produce the active type of this weevil (Fig. 3) since the relation of the larval density to the percentage of the emergence of the sluggish type was almost the same at any locality. The photoperiod also exerted its effect on the percentage of the emergence of the active type (Table 3). From these reasons, therefore, we can infer that in the whole range of the distribution, the active adults emerge during the growth-period of the bean plants, and in the local C. chinensis in which the number of generations in a year is high the number of eggs per female is small, though in the local C. chinensis in which the number of generations per year is low the relations may be the reverse.
In the previous papers (NUMATA and NIIYAMA 1953,NIIYAMA and NUMATA 1962), the authors found the existence of a critical time of weeding for cultivating the upland rice Oryza sativa var. terrestris (Norin No. 24), and a beneficial effect of weeds before the critical weeding time on the crop yield. This study is aimed at the further analysis of such beneficial effects of weeds on a crop. The field experiments were done according to the randomized block method with three repetitions, that is, Blocks : I, II, and III ; Sowing density treatments : A (5cm intervals), B (10cm intervals), and C (15cm intervals) ; and Weeding treatments : 1 (weed-free), 2 (no weeding during 5 weeks after sowing and thereafter weed-free), and 3 (no weeding during 7 weeks after sowing and thereafter weed-free). Here, 5 weeks after sowing is the maximum allowable period for weeds without decreasing the crop yield (NIIYAMA and NUMATA 1962). The plot size is 80×80cm and is divided into four squares (Fig. 1). The weed community in the experimental field is dominated by Digitaria adscendens and Th-D_4-R_5 type (Table 1). The growth of the weeds is, in genera, extremely depressed in the lowest density plots, C (Tables 3,6). The coverage of the weeds after June 19th is in the order of B>A>C. This fact suggests an optimum density of a crop for weed growth (Table 6). An extreme depression in the height growth of the weeds in C may not be caused by an effect of slender growth like in flax weeds and the extreme depression in the height growth of the upland rice on May 3rd be caused by a negative effect of the weeds growing longer over the critical weeding time. However, the recovery of crop growth in C3 is marked where a kind of crop-protective effect of weeds can be seen. Meanwhile, the dominant weed, Digitaria adscendens grows the most numerous adventitious roots on aboveground nodes in C. This may be a kind of adaptation in the growth form (Tables 4,5). Digitaria adscendens and Chenopodium album also grow best in C (Table 7). The distribution of the coverage of the weeds was most homogeneous on July 3rd in every plot (Fig. 2). The distribution of the weeds in a farmland comes, in general, to be most homogeneous in several weeks after sowing, through intraspecific and interspecific density regulation (NUMATA and SUZUKI 1958). The weeds affect the height growth and the number of heads of the upland rice in proportion to its sowing density (Tables 10,12). The growth of the upland rice becomes better after weeding in proportion to the lowering of density, particularly in C, and SDR (the summed dominance ratio) of the upland rice is larger in 2 than in 1 after August 7th (Table 13). The order of the heading time is contrary to the order of C>B>A in the plant height and the number of leaves of the upland rice in 3. This may be a kind of hunger phenomena. The crop yield in 2 and 3 increases as the density lowers (II in Table 15), and particularly the yield in C2 is larger than in C1. The total yield per plot indicates the tendency of 1>2>3 in A, but 2>1 in B and C. From the above-mentioned facts, the allowable limit of weeds (allowable quantity and critical weeding time) to a crop may be closely related with an interspecific density effect.
Morphological comparisons are made among the fourth instar larvae collected from various habitats in the northern parts of Japan. The characters used for comparison are as follows ; the number of the siphonal hair tufts (siphona hair types), siphonal index, siphonal length, siphonal width, head width, numbers of comb scales and pecten teeth, and setae of the first siphonal hair tuft. From the comparison of the siphonal hair type and siphonal index, it is concluded that morphologically different larvae can be obtained from ecologically different habitats, even though they are geographically located close to each other. Some of the morphological differences are considered to be genetical based on the results reported in the previous papers. Summarizing the results reported by various authors, there is a tendency that the siphonal index and the number of the siphonal hair tufts decrease in Culex vagans, Culex pipiens pallens (and C. p. pipiens), C. p. molestus, to C. p. fatigans in this order (however, the order is not definite between C. p. pallens and C. p. molestus). Based on the siphonal index and siphonal hair type, there were C. vagans-like, C. p. pallens-like, C. p. molestus-like, C. p. pipiens-like, and C. p. fatigans-like larvae in the larval populations observed and reported in this paper, although much discussion is needed before the subspecies names can be given to corresponding individuals mentioned above. The morphology of the adult stage should also be included to the identification. It is of interest that morphologically different larvae can be obtained from various ecologically different habitats located close to each other. The Culex pipiens group of Japan is considered to be composed of genetically different strains (or subspecies). Therefore, much pertinent study is needed before concluding that the group is a hybrid population between C. p. pipiens and C. p. fatigans or it is composed of Culex pipiens pallens.