Pupal overwintering, diapause and development in two species of Spilosoma

SUMMARY1 Pupae of Spilosoma lubricipeda (L.) and S. lutea (Hufn.) were studied in order to develop a method for estimating the date of emergence of the moths from temperature data. Diapausing pupae stored at 4–5°C for 157 and 171 days showed the fastest development on subsequent incubation at 20°C indicating that diapause had been completed in cold storage. 2 Pupae formed in August and October completed diapause in a ventilated insec‐tary in March and early April respectively. A 4‐month spread in pupation dates was compressed by diapause and low winter temperatures into a 7‐day spread in mean emergence dates for S. lubricipeda and a 17‐day spread for S. lutea.3 In the insectary, estimated mean emergence dates differed from observed dates by an average of 3.7 days for S. lubricipeda and 2.4 days for S. lutea. Pupae were over‐wintered outdoors in S. England and in Scotland. Observed mean dates of moth emergence varied with altitude and latitude, and differed from estimated dates for S.lubricipeda by an average of 5.5 days. 4 Mortality did not exceed 30% except in two years in batches kept in wet boxes outdoors at Achnagoichan which is probably beyond the breeding range of both species in Britain. In the laboratory some pupae survived exposure to — 16°C for 192 h suggesting that winter mortality alone does not control the survival of these species at Achnagoichan.