Thermal requirements of immature stages of Chrysomya albiceps (Diptera: Calliphoridae) as a common forensically important fly

Entomological material may be used to estimate the time since death occurred (postmortem interval, PMI) in forensically obscure cases. The method that is commonly used to calculate minimum post-mortem interval (mPMI, i.e., the least amount of time since one can be confident death occurred) is based on the relationship between insect development and ambient temerature. Isomegalen and isomorphen diagrams are among methods allowing to calculate the age of necorphagous insects, yet thermal summation models provide the most precise and acurate estimations. The digrams are prepared based on the length or the developmental stages of the larvae as a function of time and mean ambient temperature. A knowledge of thermal requirements, in particular lower temperature threshold (Dz) at which development of a species terminates, is of essential importance to calculate ADD (Accumulated Degree Days). In this study different temperature regimes were used to construct the isomorphen diagram, examinate changes in larval body length at different ambient temperatures and to estimate the thermal requirements for developemnt of Chrysomya albiceps, the most common dipteran species reported on human and animal cadavers in Iran. Six development events including hatching, 1st ecdysis, 2nd ecdysis, wandering, pupariation and eclosion were studied under eleven constant temperature regims (17-37 0C). The development rate of Ch. albiceps increased as temperature increased. The larval length peaked at the end of third stage and then decreased at wandering stage. The maximum larval length occurred at 72 h post oviposition at either 31, 33, or 35 C. At 17 C, larvae did not hatch from eggs and at 37 C wandering larvae did not proceed to pupariation, and thus larval development were analysed at the nine left over temperatures. The development stages required at least (Dz +/- SE) 13.04 +/- 0.37, 14.29 +/- 0.45, 15.69 +/- 0.56, 15.18 +/- 0.56, 14.94 +/- 0.48, and 11.23 +/- 0.41 C to reach one of the successive developmentl events, respectively. The estimated thermal summation constant (k) for those the six events were 10.43 +/- 0.27, 19.31 +/- 0.32, 27.87 +/- 1.3, 55.94 +/- 1.82, 66.69 +/- 3.5, and 143.52 +/- 5.61 ADD accordingly.

Automated summary

This study investigated the development rate and temperature requirements of Ch. albiceps under different temperature regimes, confirming that higher temperatures accelerate larval development and affect their body length. Parameters such as Dz and ADD are crucial for estimating later developmental events.