Third instar larvae of flesh flies (Diptera: Sarcophagidae) of forensic importance—critical review of characters and key for European species

Necrophagous Sarcophagidae are among the insects most frequently reported from human corpses. The broad forensic application of flesh flies is restricted by the lack of reliable tools for species identification of larval stages and mass breeding of collected flesh fly larvae to the adult stage, and more recently DNA-based methods are usually recommended for precise species identification. To overcome this situation, the following study was implemented: (1) original larval material was obtained of the European flesh flies of confirmed or potential forensic importance; (2) larval morphology was studied and documented using a combination of standard light microscopy, image-stacking stereomicroscopy and SEM; and (3) larval characters used in previously published keys were critically revised. The taxonomic value of the following characters was considered insignificant: (1) differences in level of sclerotisation of particular parts of the cephaloskeleton, (2) level of sclerotisation of the posterior spiracular peritreme and (3) the shape of posterior spiracular slits. A high taxonomic value was noticed for the general shape of anterior spiracles, pattern of arrangement of their lobes, and distribution and shape of spines/warts on the inter-band area of segments. Two character states—long window in the dorsal cornu of cephaloskeleton and deep spiracular cavity on anal division—are not found in the Miltogramminae and therefore cannot be considered as family-specific for the entire Sarcophagidae. As a comprehensive result of our studies, an identification key is presented for the third instar larvae of European flesh flies of forensic importance. The key is user-friendly and requires no dissections of larvae, as soaking the material in methyl salicylate will allow observation of all diagnostic details of the cephaloskeleton. A simple stereomicroscope (magnification about ×50) is sufficient for the observation of all characters presented in the key. This key may be systematically extended by the addition of species present in adjacent geographical regions.