Survival curves of the population ofdendrolimus spectabilis Bulter (Lepidoptera: Lasiocampidae)

Summary Six survival curves were drawn (Fig. 1) from a survey over two generations of the population ofDendro'imus spectabi'is Butler at three different places in the Tokyo University Forest in Aichi during the years from 1957 to 1959. The counting of insect number was done at one month interval except during the winter season. Any apparent mortality expressed as percentage decrease was not related in this survey with the density of insect population at the beginning of each interval. Considering of the magnitude and the variability of each apparent mortality, there were three critical periods of heavy decrease in the generation decline, they were; 1) September to October when newly born larvae were dispersing, 2) December to March when the third instar larvae were overwintering, and 3) August to September for the period of fully grown larvae and pupae.