Biology

Once the species on a corpse are identified, information will be needed about their biologies. Despite the fact that little research on beetles has been focussed explicitly on forensics (Williams and Villet 2006), notes and data on the development of several coleopteran species can be found in various publications. The more common and widespread species are often stored product pests, and significant research has been carried out in efforts to control these species. A good example of this is Dermestes maculatus, a cosmopolitan pest of stored products (Rajendran and Hajira Parveen 2005) that is common on mummified remains (Schröder et al. 2002). There are developmental data for this species (Scoggin and Tauber 1951; Paul et al. 1963; Richardson and Goff 2001) and notes on behaviour (Archer and Elgar 1998), control methods (Egwunyenga et al. 1998; Fasakin and Aberejo 2002) and other topics (Azab et al. 1972; Archer and Elgar 1999). Developmental data are also available for Dermestes haemorrhoidalis and D. peruvianus (Coombs 1979), but attention needs to be given to the requirements for a robust developmental model (Richards and Villet 2008). The available developmental data are summarised in Table 4.1. By amalgamating the available information on forensically important species, a balanced view of their biology can be obtained. If this is done for a variety of stored product species that also occur on corpses, such as N. rufipes and the locally common species of Dermestes (Rajendran and Hajira Parveen 2005), the information can be used to predict PMImn by community analysis. This approach essentially requires a hybrid technique that uses the developmental data to produce traditional estimates of when each species is active on a particular carcass (Villet et al. 2009, Chapter 7), and then uses these

Table 4.1 A summary of some developmental parameters already published on necrophilous Coleoptera. In cases where D0 and K were not supplied in the original publication, they were calculated according to the methods of Ikemoto and Takai (2001)

Temperature

Development

Species

(°C)

time (days)

D0

K

Source

Thanatophilus micans

25

15.7

10.3

7.62

Midgley and Villet (2009a)

Dermestes

25

40.6

12.6

26.98

Coombs (1979)

haemorrhoidalis

Dermestes peruvianus

25

52.5

11.4

44.5

Coombs (1979)

Dermestes maculatus

25

59.2

Richardson and Goff (2001)

Dermestes maculatus

Unknown

37.5

n/a

n/a

Scoggin and Tauber(1951)

estimates as refined 'windows of activity' that are analysed by the methods more usually used in community analysis (Schoenley and Reid 1987; Schoenley 1992; Schoenley et al. 1992, 1996, 2005, 2007). This incidentally allows succession data for necrophagous species to be refined to account for weather conditions through the well known effects of temperature on growth. Suitable data have been published for three North American silphids (Watson and Carlton 2005b).

It is important to analyse the beetle community as a whole, as not all beetle species will oviposit immediately after death. This delay means that the precision of an analysis using only one species will be reduced. When the biology of Dermestes spp. is used to estimate PMI , it becomes clear that adjustments may need to be made min' J •>

to the estimate because key factors modifying growth in Dermestes spp. are moisture content in food (Scoggin and Tauber 1951) and relative humidity (Coombs 1979). It is therefore important to adjust PMI estimates based on the development of these

species to account for relative humidity and dietary moisture. In cases where dietary moisture remains extremely high or low during decomposition, the development of Dermestes spp. will not give unbiased PMImin estimates as development will not occur at normal rates (Schroder et al. 2002). In these cases other species found on the corpse should be used in conjunction with Dermestes spp. for PMImin estimates, such as T. micans and other Silphidae during early decomposition and N. rufipes and Aleochara spp. in advanced decomposition. By assessing the development of as many species as possible, a crossvalidated view of the community can be obtained for analysis, making oviposition and biological variations less important and giving a more unbiased and precise PMI estimate.

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