Estudio de la entomofauna asociada a cadáveres en la Comunidad de Madrid para su aplicación en las investigaciones policiales

Résumé

Forensic Entomology is, in its most common application, medicolegal entomology, this is, the study of arthropods inhabiting decomposing remains to aid police investigations, with the main objective of calculating the Postmortem Interval (PMI). The estimation of the Postmortem Interval (PMI) can be approached in different ways depending on the decomposition stage of the remains. In the case of advanced decomposing remains, the study of succession patterns is commonly used to estimate the PMI. In this sense, knowledge of the composition of the local fauna, seasonal patterns of its succession and presence period of the species is required. In Spain, previous seasonal succession studies have been carried out in Huesca (CASTILLOMIRALBES, 2002), Murcia (ARNALDOS et al., 2004; BEGOÑA GAMINDE, 2015), Madrid (GARCÍAROJO, 2004), Alicante (VELÁSQUEZ, 2011), Badajoz, (PÉREZ-BOTE et al., 2012), Lisboa (PRADO E CASTRO, 2011) y Asturias (PERALTA et al., 2013). Nonetheless, this is the first long term Project carried out in the Iberian Peninsula and the second one in Europe (MĄDRA et al., 2015). In this Ph-D thesis we present a study conducted in the Community of Madrid, framed within a project entitled: “Forensic Entomology: study of insects inhabiting decomposing remains to aid police investigations” (Ministry of Science and Technology- BOS2003- 00400). The study was carried out on a private property from the University of Alcalá in central Spain. The area is a periurban plot with dominant ruderal vegetation, located on the Mesomediterranean bioclimatic level. Four different trials were carried out, one in each season (i): from June 2004 to August 2006, (ii): from September 2004 to November 2006, (iii): from January 2005 to April 2008 and (iv): from April 2005 to April 2008). In each trial 3 domestic pigs were used as animal models: one first control in which no arthropods were collected and two experimental replicates, carrying out arthropod samplings throughout the decomposition process. Once at the laboratory, adult specimens were identified and immature stages were reared to adulthood to be identified afterwards. Moreover, climatic data, pig weights, body temperatures and other relevant information were recorded. Five stages of decomposition were considered: Fresh, Bloated, Active Decay, Advanced Decay and Remains, each stage with durations depending on the season and ambient conditions. About 54,000 arthropod specimens among immatures (eggs, larvae and pupae) or adults were examined, belonging to more than 94 families and 346 species. Coleoptera and Diptera have been the main orders regarding presence, abundance and diversity of species. There are six species new for the Spanish fauna: dipterans piophilids Centrophlebomyia furcata and Piophila megastigmata and, on the other hand coleopterans Staphylinids Aleochara (Xenochara) cuniculorum, Atheta aeneicollis, Haploglossa gentilis and Leptacinus intermedius. Once all the specimens have been identified, those minimally abundant were selected in order to analyze three residency patterns afterwards: (1) length of the presence period, (2) breaks in the presence period and (3) longest unbroken period, as well as the consistency of the relationship between appearance time of carrion fauna and onsets of decomposition stages. A list of potential forensic usefulness of carrion fauna was elaborated in order to be applied in geographical areas similar to ours. Later, succession patterns of forensic useful species have been analyzed since composition of dipteran and coleopteran communities change along the decomposition process. Firstly, a correspondence analysis was carried out in order to associate arthropod species with the different decomposition stages, resulting this in dipterans generally more associated to Fresh, Bloated and Active decay, while most of Coleopterans associated to advanced decay and skeletal remains. Finally, succession of fauna have been stablished for each experiment carried out, observing clear differences among them regarding appearance and disappearance time of species, allowing us to conclude that taxons with higher value as forensic succession indicators are those which directly feed on the corpse as: immatures of Dipterans Calliphorids, Sarcophagids and Piophilids and immatures of Coleopterans Clerids, Dermestids, Nitidulids and Silphids. Once our results have been compared with others obtained from worldwide studies, and despite them being consistent regarding both decomposition stages, associated fauna and its succession patterns, we can highlight the necessity of developing studies with different methodologies and different environments and geographical areas in order to determine potential forensic usefulness of the fauna so as to be able to apply this tool in real cases with higher reliability.