In the present paper, the authors attempted a consideration on the density-dependency of some factors that affect the mortality of Pieris rapae crucivora, based on the survey data reported in the previous paper (ITô, MIYASHITA & GOTOH, 1960).
Counts of the eggs and the larvae on cabbage plants grown on an experimental plot covered with a net, showed somewhat biased spatial distributions as shown in Fig. 1, because ovipositing butterflies congregated near the periphery of the plot. The type of distributions could by no means be regarded as identical with that observed under open conditions. By omitting the plants grown on the periphery, however, the type of distributions became similar to that observed under open conditions reported by UTIDA et al. (1952). Indices of variance (s²/x) of the number of individuals per plant decreased as the insect grew.
Such a shift from contagious to spaced distribution was attributable to the density-proportional mortality at the egg and the first larval stages, destruction of the eggs laid in masses on peripheral plants, and density-dependent mortality and movement of mature larvae. In the second brood, the movement of larvae from larva-crowded to less crowded plants was a major factor in spacing the mature larvae, while, in the third brood, mortality by infectious diseases was thought to be the predominant factor.

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Although both the tea-tussock moth, Euproctis pseudoconspersa STRAND and the gypsy moth, Lymantria dispar L. lay their eggs in tight cluster, the larvae of the former live in compact aggregation until they reach to the last instar, while the larvae of the latter disperse out within a few days after hatching. Laboratory experiments were carried out to clear up the effect of individual number on the survival and development of the larvae of these species.
Euproctis pseudoconspersa STRAND
The larvae which hatched out from one egg-mass were reared at 1, 2, 5, 10, 20 and 40 individuals per vessel under a temperature of 23∼27°C with the natural light condition. When the larvae were kept singly or in pairs, most of them wandered and died without feeding. On the other hand, if 5 or more individuals were reared together, they made a group and developed successfully. The larval duration seemed to increase with decreasing the number of larvae in association, because the larvae in smaller groups generally took more instars. However, the pupal duration, the weight of pupa and the fecundity did not differ significantly, unless the ill effect of overcrowding was brought about.
The larvae were isolated to a solitary condition at each instar until which they had been reared in mass, and were further bred under a temperature of 27.5°C with a day-length of 16 hours. At the younger instar the larvae were isolated, the higher the mortality of them tended to be. Especially, none of the larvae isolated at the 1st to 3rd instar could survive, while those isolated after the 7th instar did not die at all. The larval duration and the number of ecdysis were increased by the isolation at younger instars. However, there seemed to be no difference in the pupal duration, the head width of the last instar larva the weight of pupa and the number of eggs per female.
Lymantria dispar L.
The larvae were reared at 1, 2, 5, 10 and 20 individuals per vessel under a temperature of 23∼27°C and the natural light condition. In every culture all the larvae developed successfully. With the increase of the number of larvae per vessel, the larval and pupal durations, the weight of pupa and the fecundity decreased progressively.
Thus, the formation and maintenance of aggregation are essential for the larval life of Euproctis pseudoconspersa STRAND and the ill effect of undercrowding is brought about by the artificial isolation of larvae. On the contrary, when the larvae of Lymantria dispar L. which show no strong aggregation are crowded together, the adverse effect of overcrowding tends to appear.

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The influence of population density upon the development was studied using the cabbage butterfly, Pieris rapae crucivora. The experiment was carried out under a constant temperature of 25°C and natural day-length.
There found some variations in larvae, pupae and adults respectively, when the larvae were reared under different densities. The changes in some internal organs, especially in the secretory organs such as corpus allatum and the suboesophageal ganglion were also examined under different densities, but there was any conclusive relation between the size of secretory organs and the bodily characters in each developmental stages.
The results obtained are summarized as follows:
From these results, it can be said that physiological activity is highest at the intermediate density than at other densities. Therefore, this density seems to be favourable for development.
It is interesting that Pieris rapae crucivora and Pieris brassicae have different ovipositing habit respectively, that is, the former deposits in patched form, while the latter in mass, but the intermediate density are favourable for the development of both two species.

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In the previous papers we discussed the geographical distribution of the two species, E. zinckenella and G. glycinivorella in Kanto-Tosan district of the country. The northern limit of distribution of E. zinckenella is indicated by an annual mean temperature of 11∼12°C and the abundant area more than 14°C. On the other hand, G. glycinivorella is found throughout the district, and the abundant area is pointed out as diluvial light soil zone.
In the present paper I made a further survey of the geographical distribution of the species throughout the country. The results obtained are summarized as follows.
E. zinckenella distributes in warmer regions of the world, and is generally. found in the tropical, subtropical and temperate zones. In Japan, it isfound in Kyushu, Shikoku, Chugoku, Tokai-Kinki, Kanto-Tosan, Hokuriku and partially the sea side area of the southern Tohoku district, but not found in cooler region of the country such as northern Tohoku and Hokkaido (Fig. 1).
As indicators of the northern limit of distribution, I suggest the following factors according to the Fig. 3:
(1) Annual mean temperature 11.5∼12.5°C.
(2) Mean temperature of warmer season (from May to October) 18.5∼19.5°C.
In Japan the applicability of the two indicators are nearly equal, but the latter will be more applicable in north China.
G. glycinivorella is found throughout the frigid, subfrigid and temperate zones of Far East. In Japan it is abundant in cooler regions such asHokkaido, Tohoku, Kanto-Tosan, Hokuriku and San-In districts, but it is not so abundant in warmer regions, i.e. Tokai-Kinki, San-Yo and Shikoku districts. In Kyushu district, southern part of the country, the species is rare in general, and not found in any island far south Kyushu (Fig. 3). It may be said that the southern limit of distribution of the species exists between Kyushu and Tanegashima Island.
As mentioned above, E. zinckenella is recognized as a typical southern species, while G. glycinivorella is a northern one. The two species, however, are commonly found in many districts of the country, from southern Tohoku to Kyushu. The abundance of the species is nearly equal in the central region of Japan such as Kanto, Tokai-Kinki, San-Yo and Shikoku districts.

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Recently the increase of damages of Japanese persimmons, Diospyros kaki, caused by wood boring beetles (Ipidae, Platypodidae, Coleoptera) were pointed out in Wakayama Prefecture. The author hereby studied the life history and control measures of the pests in 1958∼60. The results are summarized as follows.
1. As injurious wood boring beetles of Japanese persimmons 8 species, belonging to 4 genera and 2 families, are recognized. Among these species Xyleborus germanus is dominant in this district.
2. X. germanus hibernates in the adult form, and then bores the trunks or boughs of Japanese persimmons in late April or early May. One female bores one tunnel and makes several egg chambers, so called "wood family-gallery". One female oviposits 20∼50 eggs dividing into 2∼3 egg masses. The development of eggs in one egg mass is not simultaneous and both larvae and eggs usually exist in one egg mass in early June. The frequency distribution curve of the width of the head capsule of larvae separates into four peaks, so the number of larval instar seems to be four. In late part of June, newly emerged adults exist in their tunnels, but they run away in early July. The new adults, however, do not attack Japanese persimmons in the year.
3. In many cases they attack trunks or boughs of younger trees (until ten years old) as well as weekened trees. The place attacked, however, is variable according to the condition of trees. Most of the trees attacked by the beetles wither or die.
4. The results of the control experiments against the beetles by means of spraying or painting of various insecticides are shown in the following table:

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There was a reduction in the number of density-dependent diapause individuals in the original stock of Plodia interpunctella HÜBNER reared at 30°C. The percentage of density-dependent diapause decreased from 23.7% to 0.6% during three years from 1956 to 1959 (tested in the condition of 400 eggs per 30g rice bran at 30°C), whereas all or nearly all of the larvae entered diapause when they were reared at 20°C (OS).
On the other hand, by repeated breeding from the moths which emerged relatively early at a temperature of 20°C, a new stock was evolved that pupated without any interruption even under this temperature condition. This stock was also not so sensitive to larval density, showing 0.4% diapause in the condition of 400 eggs per 30g rice bran at 30°C (NS).
By the same handling method as in NS and by selecting in the opposite direction, another new stock was evolved that produced little or no diapause-free individuals in every generation at 20°C. This stock showed a marked sensibility as regards the effect of high larval density of 400 eggs per 30g rice bran at 30°C, resulting in 52.4% diapause (DS).
All the larvae of the three stocks entered diapause if they were reared at 30°C up to the middle instar stage, at which they were removed to 20°C. No larvae of the three stocks entered diapause when they were reared in a condition of low larval density at 30°C.
The significance of the results reported in this paper is that the flexibility in the character of diapause has been shown not only in the response to density independent factor but also in the mode of density response itself.

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