Estimation of the Postmortem Interval Through the Use of Development Time of Two South American Species of Forensic Importance of the Genus Lucilia (Diptera: Calliphoridae).

Obtaining the specific development time of each species of forensic interest is crucial for the estimation of an accurate and reliable Minimum Postmortem Interval (PMImin). In Argentina, Lucilia ochricornis (Wiedemann) and Lucilia purpurascens (Walker) (Diptera: Calliphoridae) were masked under the name Lucilia cluvia (Walker) for a long time still in forensic expertise. For this reason, the objective of this work is to deepen the study of the development time of these species and utilize this relevant information in the generation of different associated methods that can be used in forensics to estimate the PMI. Immature stages of L. ochricornis and L. purpurascens were reared in a brood chamber according to the following temperature treatments: 13.4, 15.1, 22.3, and 23.6°C. The development time of each stage/state of these flies was recorded as well as the resulting accumulated degree-hours (ADH), to build isomorphen diagrams and thermal summation models for each species. The development time and ADH were different between both species and their development stages. On the other hand, the methods provided for estimating PMImin provide the forensic entomologist more tools to reach accurate and reliable estimates.

Determinación del intervalo post mortem mínimo (IPM) basado en un modelo de acumulación térmica con una cepa de Lucilia eximia (Diptera: Calliphoridae) de Costa Rica / Lucilia eximia (Diptera: Calliphoridae) as forensic indicator for the calculation of the post mortem interval in Costa Rica

RESUMEN Introducción: L. eximia es una especie de amplia distribución geográfica en Costa Rica, cuyas poblaciones son estables durante todo el año. Las características biológicas de ésta permiten concebirla como un potencial indicador forense para el cálculo del intervalo post mortem mínimo (IPM). Objetivo: Comparar el IPM calculado mediante un modelo de acumulación térmica con L. eximia (Diptera: Calliphoridae), con el IPM real en cadáveres de cerdos domésticos (Sus scrofa). Material y Métodos: Dos cadáveres de cerdo fueron expuestos en un bosque premontano húmedo tropical. A partir de dichos cadáveres se colectaron larvas de L. eximia a las 78, 144 y 192 horas posteriores al momento de muerte y se propició su desarrollo en condiciones controladas. Con los datos generados, se realizaron retroproyecciones térmicas para efectuar el cálculo del IPM. Resultados: L. eximia requirió en total 7 236,50 grados- hora acumulados (ADH) para culminar su desarrollo. Los IPM calculados mediante el modelo de acumulación térmica para los tres momentos de colecta fueron 112,56; 153,60 y 104,64 horas. Únicamente el valor intermedio no presentó diferencias estadísticamente significativas con el tiempo de muerte conocido (p>0.05). Conclusiones: El modelo de acumulación térmica en que se utilizó L. eximia brindó información precisa sobre el IPM sólo cuando se tomaron las muestras en el campo a las 144 horas, lo que perfila su utilidad para las primeras etapas de la descomposición cadavérica.

ABSTRACT Introduction: L. eximia is a species that shows a wide geographical distribution in Costa Rica, whose populations are stable throughout the year. The biological characteristics of L. eximia allow it to be considered as a potential forensic indicator for the calculation of the minimum post mortem interval (PMI). Objective: To compare the PMI calculated by a thermal accumulation model with L. eximia (Diptera: Calliphoridae), with the PMI in corpses of pigs (Sus scrofa). Methods: Two pig corpses were exposed in a tropical premontane moist forest. Larvae of L. eximia were collected from the pig carcasses at 78, 144 and 192 hours after the moment of death, and their development was promoted under controlled conditions. With the data generated, thermal back-projections were made to calculate the PMI. Results: L. eximia required a total of 7 236.50 accumulated degree hours (ADH) to complete its life cycle. The IPMs calculated by the thermal accumulation model were 112.56, 153.60, and 104.64 hours, respectively. Only the intermediate value did not present statistically significant differences with the known time of death (p>0.05). Conclusions: The thermal accumulation model using L. eximia as a forensic indicator provided accurate information about the PMI only when samples were collected at 144 hours, which indicates that this method may be accurate and useful during the first stages of cadaveric decomposition.