Pupal diapause of Coloradia pandora Blake (Lepidoptera: Saturniidae)

Pupae of the pandora moth, Coloradia pandora, a Blake, were collected in central Oregon and stored at 5 degrees C for 8 to 24 weeks, then incubated at 25 degrees C. The minimum cold storage time required to break diapause was 12 weeks, but emergence rates were highest (87.5%) for 14-18 weeks. In a separate experiment, 1000 pupae were maintained in field enclosures for 3 years while soil temperature was monitored. Seventy-two percent of these pupae emerged in Year 1. Soil temperature fell below 5 degrees C for 21.7, 22.9, and 25.1 weeks over the three consecutive winters, and the minimum soil T was -2 degrees C. In the lab study, greater than or equal to 22 weeks at 5 degrees C limited emergence to <40%, therefore mortality from duration of cold could be considerable in winters such as Year 3. Prolonged (extended) diapause was observed in only 0.6% of the sample population.