Effects of Early Season Temperature on Adult Life History Traits of Wheat Stem Sawfly, Cephus cinctus (Hymenoptera: Cephidae) and Bracon cephi (Hymenoptera: Braconidae)

ABSTRACT Wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a long‐standing and serious pest of wheat, Triticum aestivum Linnaeus (Poaceae), in the northern Great Plains region of North America. Over the last decade, research efforts have aimed to better understand C. cinctus population dynamics through the use of bioclimatic and phenology models. However, some information needed to accurately parameterize a phenology model for wheat stem sawfly in western Canada is missing. In particular, the effects of early season weather on C. cinctus and one of its primary natural enemies, Bracon cephi Gahan (Hymenoptera: Braconidae) are unknown. Our study investigated how cold temperatures early in the growing season that prolong the time required for post‐diapause development subsequently affect adult life history metrics (longevity, body size, lipid content, and egg load) of C. cinctus and B. cephi through a series of laboratory assays using a thermal gradient plate to manipulate temperature. We found that male C. cinctus adult longevity and lipid content decreased in response to prolonged post‐diapause development times but that female C. cinctus were not affected. Conversely, our preliminary experiments with B. cephi indicated no effects of prolonged post‐diapause development on adult parasitoid life history metrics, but these pilot studies need to be replicated with larger sample sizes to confirm our observations. Altogether, this research increases our understanding of how cool weather early in the growing season affects the life history parameters of C. cinctus and provides preliminary data to elucidate the connectivity between C. cinctus and the parasitoid B. cephi .