Overwintering of Phyllonorycter blancardella (Lepidoptera: Gracillariidae) and its Parasites, Pholetesor ornigis and Pholetesor pedias (Hymenoptera: Braconidae) in Southwestern Ontario

Abstract

The effects of humidity, photoperiod, and length of the period of cold exposure on overwintering of the spotted tentiform leafminer, Phyllonorycter blancardella, and its two braconid parasites, Pholetesor pedias and Pholetesor ornigis, were studied in the laboratory and in the field. The length of the cold period required to terminate diapause was approximately 12 wk for P. blancardella and P. pedias. Photoperiod did not affect the development or overwintering survival of either species. P. ornigis showed little response to the length of the cold period but did not develop as quickly when reared at short photoperiods as at long photoperiods. Postdiapause development of the three species was significantly faster and survival was greater at 98% RH than at the lowest humidity (19% RH). Degree-day models were found to predict dates of 50% emergence in the field within 6 d for P. blancardella, 6–10 d for P. ornigis, and 2–4 d for P. pedias. Spring emergence of both species of parasites was well synchronized with the preferred stages (instars 1–3) of their host. Reasons for the success of P. pedias in the overwintering (fall) and spring generations are discussed.