DIAPAUSE TERMINATION AND MORPHOGENESIS OF HOLCOTHORAX TESTACEIPES RATZEBURG (HYMENOPTERA: ENCYRTIDAE), AN INTRODUCED PARASITOID OF THE SPOTTED TENTIFORM LEAFMINER, PHYLLONORYCTER BLANCARDELLA (F.) (LEPIDOPTERA: GRACILLARIIDAE)

Abstract

AbstractLow temperature is a major factor regulating diapause development in Holcothorax testaceipes Ratzeburg. Diapausing pupae required a cold period of 0°C, 5°C, or outdoor (≤0°C) for ca. 15 weeks to terminate diapause. The pupae required a further 21–27 days at 21°C for 50% emergence. Longer periods and higher temperatures of storage often were associated with shorter times of morphogenesis and duration of emergence. Percentage emergence of H. testaceipes was constant after various periods of cold storage at low temperatures. After storage at 0°C, pupae held at 21°C and a 16-h photophase reached 50% emergence sooner than those held at the same temperature but at a 12-h photophase. Photoperiod did not affect percentage or duration of emergence of the parasitoid. The threshold temperature for development of pupal H. testaceipes was estimated to be 9°C regardless of sex or host species. The thermal constant did not vary with sex of the parasitoids but differed significantly for H. testaceipes reared on Phyllonorycter ringoniella Matsumura (237 DD) and on Phyllonorycter blancardella (F.) (202 DD). Temperatures from 11 to 29°C did not affect percentage and duration of emergence from overwintered pupae, which were 75.5% and 2.4 days respectively, when reared on P. ringoniella, and 86.2% and 1.7 days respectively, on P. blancardella. These results suggest that H. testaceipes accepts P. blancardella as a host and will be synchronized with its development in Ontario.