Are the evidences of forensic entomology preserved in ethanol suitable for SEM studies?

In forensic practice, the use of arthropod evidences to estimate the postmortem interval is a very good approach when the elapsed time from death is long, but it requires the correct identification of the specimens. This is a crucial step, not always easy to achieve, in particular when dealing with immature specimens. In this case, scanning electronic microscopy (SEM) can be useful, but the techniques used to preserve specimens in forensic practice are usually different from those used to prepare specimens for SEM studies. To determine whether forensic evidences preserving techniques are also compatible with SEM analysis, we have compared specimens of all the immature stages of Calliphora vicina Robineau-Desvoidy, 1830 (Diptera, Calliphoridae) preserved in 70% ethanol, with others prepared with aldehydic fixative techniques that are more appropriate for SEM studies. At the same time, two drying techniques have also been compared with both fixative techniques, the critical point drying and air-drying following with hexamethyldisilizane treatment (HMDS). Our results indicate that there are not basis against recommending the use of ethanol to preserve forensic entomological evidences and that both drying methods appear to offer good results for second and third instar larvae, although HMDS behaves better with eggs and pupae.

Morphology of preimaginal stages of Calliphora vicina Robineau-Desvoidy, 1830 (Diptera, Calliphoridae): a comparative study.

A comparative morphological study of preimaginal stages (larvae and pupae) of Calliphora vicina Robineau-Desvoidy, 1830 is presented. The entomological samples came from laboratory colonies bred under controlled environmental conditions (25°C and 60% relative humidity). In this study, a recently published technique to clear Diptera larvae for light microscopy and a standard protocol for scanning electron microscopy were used. For the morphological comparison of larval instars I, II and III, and pupae of C. vicina, different larval regions (cephalic, thoracic and abdominal, including anal division), as well the internal chitinised cephalopharyngeal skeleton, were considered separately. Our results focus on showing the changes observed throughout development for the most important structures in the cephalic region (sensilla of maxillary palpus, antennae and oral ridges), the thoracic region (the first segment and its anterior spinose band) and in the anal division of the abdominal region (posterior spiracles and shape of the papillae). In addition, some morphological structures are described or pictured for the first time, such as the ventral organ and the anterior spiracle of larva I and the antenna sensilla, Keilin's organ and wrinkled area of the anal division of all instars. The cephalopharyngeal skeleton is an important structure for the taxonomy of Diptera larvae in all instars, including Calliphoridae. Our observations in C. vicina indicate that an in-depth review of the sclerite composition is needed. Pupae and larvae stages can only be compared by following the segmentary spinose bands and the anal segment, where the morphology of the posterior spiracles and papillae can be observed, in some cases despite the reduced condition of the latter.