Abstract
The annual life cycle, and the seasonal and spatial changes in numbers and the age structure were investigated in a natural population of the smoky brown cockroach, Periplaneta fuliginosa S. Results obtained by the live trapping in a shed with regular intervals were as follows : 1. The largest number of cockroaches were captured in June. It seems to be due to the hatching of a vast number of nymphs and the high activity of cockroaches due to hot and humid weather in this month. 2. The seasonal change of the age structure indicated that the 'two-year life cycle' was normal in a natural population of the smoky brown cockroach, as Tsuji and Mizuno (1972) pointed out. The age structure in a overwintering population changes year to year partly because of this 'two-year life cycle', and the seasonal incidence of hatching, adult emergence etc. during successive active seasons may be roughly predictable from the age structure in the previous overwintering population. 3. The density and/or the instar composition were different from room to room and trap to trap, and these differences were clearer in young instar nymphs than old nymphs or adults. Assuming that the spatial differences in the number of insects being trapped reflects the spatial distribution in the shed, the distribution pattern was analysed by using the m^^^*-m^^^- relatioship method (Iwao, 1968). It was found that the distribution pattern was highly aggregative in all development stages. But this tendency was weakened in the following order : 1st-3rd instar nymph (β=8.0)>over 4th instar nymph (β=5.3-6.2)>adult (β=3.7). The degree of aggregation also changed seasonally. It was low in active seasons and high in inactive ones.
