In this paper an attempt was made to make clear the faunistic composition and its seasonal change in a cabbage field of spring and autumn.
The all insects on cabbage field were collected weekly from early April to late May of spring and early October to late November of autumn in 1963, and obtained results were treated after MOTOMURA'S geometrical progression formula (1932).
The composition of the major species in a cabbage field are shown in Table 1 and 2.
The succession of structure of insect community in a cabbage field was summarized as follows;
(Spring field)
PiRC. Ap-association in the middle to the latter part of April-PiRC・Ap・PIN-association in early and middle May→PiRC・Ap・PIN・BaB_association in the middle to the end of May.
(Autumn field)
Ap・BaB_association in the beginning to the end of October→Ap・BaB・PiRC・PIN-association in the beginning to the latter part of November.
The geometrical progression formula Log y + ax = b, given by MOTOMURA (1932) are shown in Table 3 and Figure 2 - 3.
Where "y" is the number of individuals of one species per unit area, "x" is the rank in individual number of each species, the value of "a" is a constant indicating the complexity of association and value of "b" is a constant showing the population density of the association.
The number of individuals was observed to increase from April unitil May, and the faunistic composition was most complex in the middle to the latter part of May. At the beginning to the middle in October, the fauna showed the most simple in the composition though the population was high, but in the later part October to the end of November it became complex.
The most important injurious insects in a cabbage field were Pieris rapae cruivora, Plusia nigrisigna, Barathra brassicae and Aphidiae.