Abstract
In Japan it is said that Dendrolimus spectabilis has usually one generation a year, but in some localities a part of its population appears to have another generation. For investigating the voltinism of D. spectabilis with its life cycle, this work was carried out under field and semi-natural conditions at Kyoto City in 1967 and 1968. The development of larvae and the date of adult emergence were studied in relation to the body size of overwintered larvae and to the date of egg hatching. The results were as follows: The larvae overwintered at the 4th to the 7th instar. The larvae hatched in earlier season overwintered at the more advanced instar. The larvae overwintered in the advanced stage tended to emerge in earlier date of the following summer. A part of the larval population which had hatched in the middle of July emerged as adult in September and passed another generation in the same year, while the remaining part of the population overwintered at the 5th to the 7th instar of larvae. The larvae of the second generation overwintered at the 4th instar. From the results mentioned above, it was concluded that a part of the population passed its life cycle once or twice a year, while the considerable part of the population had a peculier life cycle in which adult emerged once and twice a year, alternatively.
