Effect of fluctuating temperatures on the development of forensically important fly species, Chrysomya megacephala...

Necrophagous blow flies are a commonly used forensic tool to estimate the minimum postmortem interval (PMI_min), where researchers collect development data under constant temperature regimes and construct models to estimate PMI_min. However, the ambient temperatures of real death scenes are often fluctuant, which limits the reliability of data obtained under constant temperature regimes. Here we investigate the possible differences in the development of Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae), an important species in forensic entomology. Chrysomya megacephala was exposed to nine temperature regimes with both large and small fluctuations, including a 19℃ constant temperature (19CT), 19℃ average with fluctuating temperatures 1 (19FT1) (16-22℃), a 19℃ average with fluctuating temperatures 2 (19FT2) (12-30℃), as well as 25CT (25℃), 25FT1 (22-28℃), 25FT2 (16-34℃), 28CT (28℃), 28FT1 (25-31℃) and 28FT2 (18-38℃). The total developmental durations of C. megacephala were 463.94 h (19CT), 534.50 h (19FT1), 507.78 h (19FT2), 273.70 h (25CT), 293.80 h (25FT1), 302.89 h (25FT2), 230.00 h (28CT), 245.84 h (28FT1) and 265.17 h (28FT2), respectively. The results showed that the developmental time of C. megacephala under fluctuating temperatures was longer than at constant temperatures. Except for 19℃, large amplitude fluctuating temperatures resulted in more developmental delays. Although there were numerical differences in the developmental time of almost all the stages of C. megacephala at fluctuating temperatures compared with constant temperatures, the Kruskal-Wallis test only found statistically significant differences during a few developmental stages (p < 0.05). We also used the larval body length equations constructed with constant temperature data to verify larval growth at fluctuating temperatures and found that there was a deviation between the estimated development time and the actual development time. These results are reference for the application and correction of C. megacephala data, aiding in the accurate estimation of PMI_min.