幼虫期の米糠内での移動と生息密度コナマダラメイガの増殖能力におよぼす生息密度の影響VIII

抄録

The distribution of the individuals of the almond moth, Ephestia cautella, within the layer of rice-bran which was given as their larval food was observed in relations to their stage of development and to their population density, under the experimentally controlled condition of 30℃ and about 70 per cent of relative humidity. At the beginning of the experiment, the eggs were scattered on the upper surface of the ricebran. The height of 20 grams of rice-bran in a container which was a paper box of (4×4)cm^2 in surface was about four cm at the beginning of the experiment, but it decreased with the progress of the larval development especially at high density of population. The rice-bran was divided into three layers of equal weight. In the experiment I, the counting of the number of individuals in each layer of the rice-bran was made at five days interval, and the width of their head capsules was measured to estimate their degree of development. On the other hand, in the experiment II, the population in each layer was reared separately, and the number of emerged moths was counted every day to estimate the number of individuals in each layer of the rice-bran at the time of its separation and the degree of their development at that time. Almost all of the larvae of young stage stay in the upper layer at both high or low densities. The movement of the larvae towards the middle and the bottom layers begins at the third instar and becomes frequent towards the final instar. The proportions of individuals at the middle and the bottom layer become high with increasing density, until the number of individuals in each layer becomes almost equal. The larvae in the lower layer are slightly more advanced in their degree of development than the larvae in the upper layer. The fully grown larvae move upwards, searching for a pupation site and pupate at the upper layer. Some of the individuals wander and pupate at the outside of the container when the density is high. It is concluded that the upward movement of fully grown larvae does not depend upon their density, while the downward movement of the young larvae and the escaping of the larvae of all stages from the container depend upon their density and occur only when the contact among the larvae is frequent. Some consideration were given comparing with the result of the author's preceding experiment (TAKAHASHI 1955), in which the larvae can emigrate from one vial to another.