Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 95(1): 135-138

Departamento de Parasitologia, Instituto de Biologia *Departamento de Medicina Legal, Faculdade de Ciências Médicas, Universidade Estadual de Campinas, Caixa Postal 6109, 13083-970 Campinas, SP, Brasil

Received 15 April 1999
Accepted 9 September 1999

Necrophagous insects, mainly Diptera and Coleoptera, are attracted to specific stages of carcass decomposition, in a process of faunistic succession. They are very important in estimating the postmortem interval, the time interval between the death and the discovery of the body. In studies done with pig carcasses exposed to natural conditions in an urban forest (Santa Genebra Reservation), located in Campinas, State of São Paulo, southeastern Brazil, 4 out of 36 families of insects collected - Calliphoridae, Sarcophagidae, Muscidae (Diptera) and Dermestidae (Coleoptera) _ were considered of forensic importance, because several species were collected in large numbers both visiting and breeding in pig carcasses. Several species were also observed and collected on human corpses at the Institute of Legal Medicine. The species belonged to 17 different families, 6 being of forensic importance because they were reared from human corpses or pig carcasses: Calliphoridae, Sarcophagidae, Muscidae, Piophilidae (Diptera), Dermestidae, Silphidae and Cleridae (Coleoptera). The most important species were: Diptera _ Chrysomya albiceps, Chrysomya putoria, Hemilucilia segmentaria, Hemilucilia semidiaphana (Calliphoridae), Pattonella intermutans (Sarcophagidae), Ophyra chalcogaster (Muscidae), Piophila casei (Piophilidae); Coleoptera _ Dermestes maculatus (Dermestidae), Oxyletrum disciolle (Silphidae) and Necrobia rufipes (Cleridae).

Key words: forensic entomology - Diptera - Coleoptera - carrion insects - decomposition - death time

The decomposition of a dead body starts firstly through the action of microorganisms such as fungi and bacteria, followed by the action of a series of arthropods, with the predominance of the sarcosaprophagous insects (Nuorteva 1977). Notable differences were noted in the decomposition process, basically related to time of disintegration, being faster in the presence than in the absence of insects (Payne 1965, Jirón & Cartín 1981).

After death, the body undergoes natural changes, going through different stages of decomposition that are attractive to necrophagous insects. According to Bornemissza (1957) the decomposer community of a carcass goes through a process of ecological succession. Therefore, the insects arrive in a determined sequence, producing an addition and/or substitution of species. Knowing this sequence as well as their preference for the different stages of decomposition, and the meteorological data, it is possible to determine the postmortem interval (PMI). Insects can also verify the cause of death and if the body was moved (Catts & Goff 1992, Anderson 1997).

The basic reason for using insects in criminal investigations, a science denominated as forensic entomology, resides in the fact that insects are the first ones to detect and to find a cadaver and are present in all stages of decomposition and, furthermore, some species are specific for certain areas and seasons. Another important point to be considered is that oviposition can occur minutes after death (Smith 1986). It is interesting to point out that insects of forensic importance are those that do not just visit the corpse or carcass in the adult form, but also breed in these substrates because, by knowing the developmental time of their larvae, it is possible to estimate the time of death.

Our objective was to determine the insects that are of importance in estimating the time of death for the study area. Samples were collected from pig carcasses exposed to a natural urban forest and from human corpses at the Institute of Legal Medicine (ILM) in the area of Campinas, State of São Paulo, Brazil.

The study was done in two different environments: in a natural forest area (Santa Genebra Reservation) and at the ILM, both located in the city of Campinas, State of São Paulo. The data were collected from 1994 to 1998.

In the natural area (Morellato & H Leitão-Filho 1995), 16 pig carcasses (Sus scrofa Linnaeus) weighting approximately 10 kg each were used as baits. They were killed mechanically with a blow to the head and by mechanical asphyxia and immediately placed inside metal frame cages to exclude large vertebrate scavengers. Underneath the cages, metal trays with sawdust were placed to collect larvae leaving the carcasses to pupate. The adult insects were captured from pigs by emergence traps, consisting of an iron frame in form of inverted funnel and covered with transparent fabric. The immature forms (maggots and pupae) were collected through daily screening of the sawdust placed under the bait and were deposited in plastic vials covered with transparent fabric, to prevent the escape of adults after emergence. Each experiment lasted until the entire carcass had been consumed. At the ILM, the adult insects that were attracted to 20 human bodies or were transported with them to the morgue, were collected with an insect net. The maggots were collected with forceps, deposited in plastic vials, transported to the laboratory, where they were kept and reared until the eclosion of the adults. The collections were made once a week, in the morning. The collected and reared insects were later counted and identified. The Calliphoridae was identified according to Dear (1985).

RESULTS

Table II and Table III present data on the frequency of the species of forensic importance that were collected in the natural forest and at the ILM.

An exposed body represents a temporary habitat and food source for a variety of organisms that extend from bacteria and fungi to vertebrates. Regarding the experiment done in the forest, the insects were the most important decomposition agents of the pig carcasses, being present during all the stages of decomposition. The Diptera had a peak during the initial stages, and the Coleoptera during the final decay process.

The diversity of insects collected in the natural environment was much larger than at the ILM and several corpses in the morgue had insects that came from natural environments. This may be due to differences in attractiveness exerted by the different species, or to the smaller sampling effort spent at the IML, or both. However, the adult flies that were attracted to the corpses at the ILM were the same species that were collected in the pig carcasses and are important forensic indicators. Chrysomya albiceps, C. megacephala, Hemilucilia semidiaphana and Pattonella intermutans were the most frequent. Most of the Coleoptera can be considered incidental visitors, and only a few species can be considered to be forensic indicators: Dermestes maculatus, Oxylletrum disciolle and Necrobia rufipes.

Of the 54 collected species, 28 are of forensic importance and can be used as indicators of the PMI and of the area, because they were reared from the carcasses or they occurred in just one environment or season. The insects collected in both environments can provide the initial data for additional studies to improve the knowledge of the carrion arthropod fauna in the area of Campinas.

The insects can be useful tools in investigations on causes and circumstances of death. However, the usefulness of this method depends on how the corpse has been handled before the arrival of the entomologist at the death scene. Ideally, the forensic entomologist should be part of the team of professionals that are first called to the death scene.

ACKNOWLEDGEMENTS

To the Santa Genebra Foundation and the Institute of Legal Medicine, Campinas, which made this study possible. To Dr Julio Mendes for help with the identification of the Sarcophagidae; to Dr Cláudio JB Carvalho for help with the identification of Muscidae; and to Fernando V Mello, Marcelo Mattos and Sérgio L Gianizella, for help with identification of the Coleoptera.

Work supported in part by Fapesp, grant no. 93/3927-2 and Faep, grant no. 0115/94.

REFERENCES

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