Validating the use of a local developmental dataset for Cochliomyia macellaria (Diptera: Calliphoridae) to estimate the time of placement of various carrion types and sizes in Texas, United States, during summer.

Accurate estimation of the time of colonization (TOC) is a cornerstone of forensic entomology, yet direct validation of laboratory-derived development datasets in field contexts remains rare. Within validation studies, when the TOC is unknown, the time of placement (TOP)-the point at which remains become accessible to insects (e.g,. Diptera)-can serve as a proxy. This study evaluated the accuracy of Cochliomyia macellaria (Diptera: Calliphoridae) development estimates under varying ecological conditions by calculating the estimated-to-actual TOP ratio (%). Factors examined included carcass type (small, medium, and large mammals; large birds), thermal summation method (accumulated degree days [ADD] vs. accumulated degree hours [ADH]), emergence timing (first vs. last emergence), development dataset tissue source (porcine vs. equine), and species coexistence with Chrysomya rufifacies (Diptera: Calliphoridae). A full-factorial, aligned rank-transformed ANOVA was conducted using three replicates per carcass type across two Texas field sites in 2023 and 2024. Using ADD, first-emergence data, and porcine-derived tissue consistently yielded the highest TOP ratios (93.9%, 96.3%, and 93.4%, respectively). Precision was greatest in small mammals and lowest in large mammals. Although ADD-based estimates generally outperformed ADH, ADH occasionally demonstrated greater consistency under certain contexts. Species coexistence and trial year showed context-dependent influences on TOP ratio outcomes. These findings underscore the importance of incorporating ecological and biological variability when applying development studies to forensic casework and highlight the robustness of ADD calculations and early-emergence sampling for estimating TOC in the field.