Thermal requirements for the development of immature stages of Fannia canicularis (Linnaeus) (Diptera: Fanniidae)

Abstract Entomological material may be used to estimate the time since death occurred (minimum post-mortem interval, mPMI) in forensically obscure cases. The method commonly used to calculate mPMI is the application of a thermal summation model. Little is known about the thermal requirements of Fanniidae. To fill this gap, the influence of temperature on the development time of Fannia canicularis (Linnaeus), a cosmopolitan species with the potential to be used in forensic entomology, was studied. An experiment was performed under nine ambient temperatures. The thermal summation constants ( k ) and developmental zeros ( T min ) of this species were calculated for six developmental events: hatching, first ecdysis, second ecdysis, wandering, pupariation, and eclosion. Data were primarily analysed with two linear models, and then, since the relationship between temperature and development rate is curvilinear close to the lower and higher developmental thresholds, the relationship was also modelled using three nonlinear models. A fourth nonlinear model was also used to estimate the intrinsic optimum temperature of F. canicularis , at which the population size is maximal and the mortality is the lowest. At 33 °C, larvae did not hatch from eggs, and thus changes in larval body length were analysed at the eight remaining temperatures. Fannia canicularis development from egg to eclosion required a mean ± SE of 481.73 ± 9.89 degree-days above a lower threshold temperature of 4.64 ± 0.19 °C. At the lowest experimental temperature tested, 10 °C, F. canicularis successfully completed all developmental events, although ca. 30% of wandering larvae proceeded to the inactive stage instead of pupariation. Results obtained from nonlinear models were not satisfactory and did not allow us to consider them as reliable from a biological point of view.