Insects

13.6.2.1 Calliphoridae

Calliphoridae may be collected from shallow graves. Their study can help to estimate a minimum PMI, because delay caused by burial cannot be determined. Moreover, colonization of the corpse before burial cannot be excluded. In this situation the estimate is more accurate. Turner and Wilshire (1999) suggested that cold and anoxic conditions in a heavy clay soil had preserved the carcasses and significantly delayed the arrival of Calliphora vomitoria. The use of this species would have led to a wrong estimation of PMI.

Wyss and Chérix (2006) observed oviposition of Calliphora vicina and Calliphora vomitoria 12 days after the disposal of a bait at 10 cm depth at the bottom of an abyss in the dark. The average temperature was 5°C. In this situation, the location of the substrate delayed attraction of insects but did not stop it. They concludes that death of the hill-walker occurred just after his disappearance. The absence of light is not a sufficient criterion for considering egg-laying to be a nocturnal phenomenon. Authors did not observe in which period of the day they occurred (probably a diurnal period). Indeed, photoperiod has a hormonal and maternal determinism. Modifications in the circadian rhythm are known to be observed in the following generation and not in the actual one (oviposition).

Absence of Calliphoridae in the samples associated to the study of environmental conditions (weather station) of the scene of death may indicate (if conditions are favourable) that time elapsed between death and burial was shorter.

Forensic entomologists may have difficulties in estimating PMI when species that are hard to identify are collected, such as Sarcophagidae and Phoridae (3,000 species in the world). The main consequence in this situation is also the lack of development data of some species in these families.

13.6.2.2 Muscidae

Megnin described Muscina stabulans within the first wave on buried carrion. The chronological succession pattern observed by Vanlaerhoven and Anderson (1999) between Calliphoridae (Calliphora vomitoria) and Muscidae (Hydrotaea sp., Morellia sp. and Ophyra leucostoma) suggested interesting developments to estimate PMI. In shallow graves genus Ophyra and Muscina were described as predominant (Lundt 1964). If Calliphoridae are not observed, development data of species belonging to these genuses may be interesting to estimate the minimal period of insect colonisation after burial.

13.6.2.3 Phoridae

Their study does not necessarily provide an accurate estimate of the PMI as these flies do not mandatorily appear at the surface after the first generation. Smith (1986) also suggested that many generations could breed in the coffin, as many adults and puparia could be found in many exhumations. However, it is possible to estimate a minimum PMI of burial basing the analysis upon puparia that are found, considering that the period of emergence can at least occur at the moment of collection. Some authors (Disney 1994) suggested that some Phoridae collected on buried carrion may play a similar fonction to Calliphoridae in exposed ones.

Greenberg and Wells (1997), Leclercq (1999) wrote that Phoridae adults are known to arrive at a body with a delay in comparison with Calliphoridae or Sarcophagidae, observed in early stages of decay, suggesting they could not be necessarily associated as insects of secondary forensic importance. During the winter period, Manlove and Disney (2007) estimated in a case example a PMI with Megaselia abdita (Schmitz), whereas Calliphoridae were collected. At the temperature taken into account by authors, the Phoridae provide a longer life cycle and therefore provide a better PMI than the Calliphorids usually analysed.

13.6.2.4 Stratiomyidae

Hermetia illucens (Linné) (Stratiomyidae) is a widespread Diptera (Leclercq 1997). Lord et al. (1994) collected H. illlucens in a corpse from a grave site and used its development time to estimate the PMI. Lord et al. mentioned that H. illlucens was frequently predominant on remains in the drier post-decay stage of decomposition above ground. A late arrival (colonization of exposed corpses 20-30 days post mortem), associated with its life cycle duration, may provide longer estimates according to the authors. It could be a potential PMI indicator whose development can be used in combination with data of other arthropod species. However, further studies (Tomberlin et al. 2005) in the United States did not confirm a late arrival but rather an early one (6 days post mortem) as confirmed by Pujol-Luz et al. (2008) in Brazil (3 days).

13.6.2.5 Coleoptera

The Coleoptera rarely colonize a carcass at early stages, as suggested by the authors (Shubeck 1968), because of a lack of efficiency in detecting carrion for some of them. Thus their forensic importance is lesser than Diptera. Staphylinidae, Histeridae and Silphidae are mainly collected on buried carcasses or corpses (Lundt 1964; Smith 1986; Leclercq 1978; VanLaerhoven and Anderson 1999), mainly from shallow graves (<30 cm deep). In coffins, Staphylinidae seems to be the only family observed (Mégnin 1894; Motter 1898; Smith 1986; Bourel et al. 2004; Merritt et al. 2007) as in deep graves (about 90 cm deep) (Payne et al. 1968). Moreover, many of them are generally predators or immature stages of Dipterans. Their arrival is not directly in relation with the presence of the corpses. For all these reasons Coleopterans collected on a buried cadaver and its surroundings cannot be considered as reliable forensic indicators, and are almost never used to estimate PMI.

The relation highlighted by Hakbijl (2000) between the occurrences of Rhizophagus paralellocolis (Gyllenhal) and the presence of fungi present on the cadavers may be interesting. The association of growing data of fungi in addition to thermo-dependent development time of this species may help to estimate PMI.

13.6.2.6 Hymenoptera

Females of Nasonia vitripennis usually lay eggs in their host (pupae of Calliphoridae, Muscidae) 1 day after the pupation when the skin of the larva has separated from the inner pupal cuticle. In this situation the forensic entomologist can only assess

damage in the rearing: no adult flies' eclosion but pupae with little circular holes in the cuticle (Fig. 13.4). Thus, PMI estimation is hardly possible. Moreover, the tiny adults of parasitic wasps observed in the incubator are susceptible to contaminate other rearing boxes and compromise other analyses. Grassberger and Frank (2003) studied the temperature-related development of N. vitripennis using host of pupae of Protophormia terraenovae (Robineau-Desvoidy) (Diptera, Calliphoridae) in order to allow estimating an extended PMI. They confirmed a development time inversely related to the temperature for this species and defined a lower threshold and ADD summation from 15°C to 30°C, thus suggesting to use this as a reliable forensic indicator for estimating PMI. This approach is promising but further research is necessary.

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