During 2024 and 2025, experimental lines and released varieties were entered into a field test trial in central Texas. This wheat-growing area in McLennan County is known both as a latitude supporting multiple generations of hessian flies per season and an area where resistance to this pest is regularly observed breaking down at the field level. Indeed, resistant varieties see regular infestations in this region, and the Wheat Improvement Team considers findings from this area a potential precursor to trends further north in Oklahoma. 
 
Small plots were established early each growing season to maximize fly exposure and were arranged as a mosaic of entries with previously determined or expected antibiotic resistance to the fly. Antibiotic resistance refers to a plant trait that prevents survival and development of flies and is independently verified in USDA-Agricultural Research Service greenhouse assays, but non-preference can also be tested using this mosaic because hessian flies lay eggs differently among entries. In April of each year, multiple plants from each plot were dug up and returned to the lab, where hessian fly larvae and pupa were counted within 5-10 tillers for each entry. 

 

Infestations above 1 fly per tiller are considered economically significant, and our susceptible entry (TAM 205) harbored relatively high populations each year, indicating the location is an excellent evaluation site (Table 1). Fly populations varied between years, but 2024 infestations indicated that flies are laying large numbers of eggs and surviving on previously resistant Duster and several experimental lines in the breeding program. Gallagher and more recently released OSU varieties appear to be holding up, indicating more complex resistance mechanisms than previously thought. Complex resistance incorporates unstudied non-preference mechanisms, and a large number of entries in the program appear not to be preferred for egg laying when given a choice. At the field level, this mechanism can break down when flies do not have a choice, but this hypothesis requires more detailed studies. 
 
Our results could be important for expectations regarding candidates for release in 2026 and beyond, particularly OK23D89031X, OK23D89055X, OK23D89088X and OK249A26X.  Most had very low infestations in our Texas trial, but OK23D89031X harbored economic infestations. Variety choice when considering hessian fly is based on local infestation levels because they are poor flyers. So, with low local populations of flies, varieties addressing disease concerns and agronomic goals are more important.