Effects of early season temperature on adult life history traits of wheat stem sawfly, Cephus cinctus (Hymenoptera: Cephidae) and Bracon cephi (Hymenoptera: Braconidae)

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, information is missing that is required to accurately parameterize a phenology model. In particular, the effects of early season weather conditions on C. cinctus and one of its primary natural enemies, Bracon cephi Gahan (Hymenoptera: Braconidae) are unknown. Our study investigated how cold early season temperatures that increase the time required for post-diapause development affect adult life history metrics (longevity, body size, lipid content, and female egg capacity) of C. cinctus and B. cephi through a series of laboratory assays using a thermal gradient plate to manipulate temperatures. We found that male C. cinctus adult longevity and lipid content decreased in response to prolonged post-diapause development time but that females were not affected. Conversely, B. cephi adult longevity (male and female) did not change under the same experimental conditions, suggesting that B. cephi is likely to stay in-sync with C. cinctus and remain as an important natural enemy. Altogether, this research increased our understanding of how early season temperatures affect C. cinctus life history parameters. This information can be used to parameterize a phenology model for C. cinctus that includes the contribution of B. cephi on its population dynamics and that could subsequently be used to forecast C. cinctus pest status population dynamics across its geographic host range.