Estudio ultramorfológico comparado de los estadios pre-imaginales de dípteros sarcosaprófagos de interés forense(Insecta-Diptera)

Abstract

Abstract The morphological study of preimaginal stages of sarcosaprophagous dipteran is essential for the newest practices to estimate the postmortem interval (PMI). The microscopy techniques are indispensable due to the small size of some stages and structures of taxonomical interest such as the egg and first instar larvae. Scanning electron microscopy (MEB) is at present the microscopy technique most used, but the current tendency points to combine it with optical microscopy (MO) to allow study internal structures. Taking into account the above we planned accomplish the following objectives: 1) to describe and characterize morphologically the preimaginal stages of five species of Diptera of forensic interest, belonging to the families Sarcophagidae (Sarcophaga (Liopygia) cultellata Pandellé, 1896 and Sarcophaga (Liosarcophaga) tibialis Macquart, 1851, Muscidae (Hydrotaea capensis (Wiedemann, 1818) and Synthesiomyia nudiseta (Van der Wulp, 1883), and Piophilidae (Piophila megastigmata McAlpine, 1978, applying MO and MEB techniques; 2) to determine the features of taxonomical usefulness allowing doubtless differentiate and identify each stage. All the studied specimens were bred at the Forensic Entomology Laboratory of the Faculty of Biology of University of Murcia (Spain), under controlled conditions of relative humidity, temperature and photoperiod. Selected specimens of each preimaginal stage (egg, larval instars I, II and III and puparia) were sacrificed following the protocol proposed by the European Association for Forensic Entomology (EAFE) (Amendt et al. 2007) and processed for analyzing with MO and MEB following the methodology proposed by Ubero-Pascal et al. (2005, 2012). For each preimaginal stage a detailed description of its micromorphology is given. Concerning the egg it has emphasized show design and organization of the plastron, the hatching line and the chorion ornamentation. To describe the larval stages the body regions considered by Courtney et al. (2000) has been followed, that is, pseudocephalon, thorax, abdomen and anal division. It has been offered a detailed description of complex sensorial structures (antenna, maxillary palpus, facial mask, ventral organ, ¿), cephalopharyngeal skeleton, fore and hind respiratory spiracles, single sensorial elements (Keilin organs, posterior papillae, anal tubercles,¿) and pattern of spinose bands and ornamentation of each body segment. The puparium shows morphology very similar to that of the third instar larva, but some structures, such as the pseudocephalon and some elements of the anal division are usually collapsed or quite contracted. All the information above allowed correlating all the immature stages of one given species. It can be observed that some structures become more complex along the life cycle while others remain more or less unchanged. At the same time, such structures allowed characterizing taxonomically each species, differentiating each other and with other species the description of which is available at the literature. Moreover, wherever possible and based on that data, structural elements allowing differentiate supraspecific taxa have been identified.