Necrophagous insects such as blow flies (Diptera: Calliphoridae) are considered crucial in forensic entomology. Identification at species level and determination of larval stage are the basis for estimation of postmortem interval (PMI). Insect evidence can also be used in the determination of crime scenes, since body displacement is common. The aim of this study was to determine the chemotaxonomic profile and intraspecific variability of the forensically important blow fly Chrysomya megacephala (F. 1794). Adults were collected in the municipalities of Dourados-MS (Brazil) and Rio Claro-SP (Brazil), and then transferred to the laboratory for oviposition and development of the immature stages. Chemical analysis of cuticular compounds was performed by gas chromatography. Cuticular chemical profiles varied significantly between the two populations, as well as between developmental stages, supporting the use of these compounds as a complementary tool to help identify the species and its stages, along with geographical variability. This could greatly accelerate forensic investigations, eliminating the need to allow the fly larvae to develop until adult stage in order to confirm the species identity and sample origin.
Blowflies use their sense of smell to locate oviposition substrates and their vision to direct and assist in landing decision. Blowflies' ovipositions are usually aggregated. Chrysomya megacephala (Fabricius) females, for example, prefer to lay eggs on substrates containing fresh eggs of the same species. However, it is possible that females would be capable of evaluating the substrate, reducing the size of egg cluster in sites with a high amount of eggs or larvae, or finding another site for laying their eggs, preventing the progeny from facing high competition for space and food. The present study aimed to investigate whether females of C. megacephala could distinguish and preferentially select previously infested substrates and whether females would lay their eggs attached or separate from eggs previously laid on the substrate. Behavioral measures were conducted inside cages under laboratory conditions in free-choice tests. Data analysis confirmed that C. megacephala females are able to distinguish the presence of cospecific eggs in the substrate and preferentially select previously infested substrates for egg laying, depositing their eggs separate from pre-existing large egg masses.
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