Effects of photoperiod on development of the pine caterpillar, Dendrolimus spectabilis (Lepidoptera: Lasiocampidae)

The experiments were carried out in order to find the effects of photoperiod on development of the pine caterpillar. The larvae were collected from different places and reared mainly in incubators at 25°C under different artificial photoperiods. The results were as follows: 1) The larvae entered diapause under short-days but not under long-days. 2) The critical day-length was 15.0-15.5 hours for the Muramatsu (Ibaraki Pref. ca. 36°25′N) stocks, and 14.5-15.0 hours for the Yamakawa (Kagoshima Pref. ca. 31°15′N) ones. 3) The larvae of the diapause type needed more than 64 days to grow to the end of the 5th instar, and most of them were still in the 6th-9th instars in about 100-150 days after hatching. On the other hand, the non-diapause larvae generally completed their development at the 6th instar in 49.9-72.5 days. 4) The non-diapause larvae were clearly distinguished from the diapause ones in size and colour at the 5th or 6th instar.