Blowfly larvae have an assimilation efficiency of about 80% (Hanski 1976), and mature larvae weigh 75-100 mg, so each one needs at least 90-120 mg of food to complete development. There is circumstantial evidence that this figure is in fact about 200 mg of pig's liver, 500 mg of pig's muscle or 1,000 mg of pig's brain in Calliphora vomitoria (Linnaeus) (Ireland and Turner 2005). However, C. vicina and L. sericata developed best on pig's lung (and brain or heart), and worst on pig's liver (Clark et al. 2006; Kaneshrajah and Turner 2004). Calliphora augur (Fabricius) and Lucilia cuprina (Wiedemann) grew significantly better on sheep's meat and brain than on sheep's liver (Day and Wallman 2006b). Chrysomya albiceps grew larger on horse meat than on sardines (Cardoso Ribeiro and Veira Milward-de-Azevedo 1997), while L. sericata grew faster and larger on pig than on cow tissues (Clark et al. 2006). These studies imply that the nutritive value of different tissues and different animals varies, that different insects respond differently to that variation. This is probably also true of human tissues, but the magnitude of the effect is unknown.

There are reports of variations in mean developmental time of up to 2 day (out of 6-8 day) at 20°C (Ireland and Turner 2005; Kaneshrajah and Turner 2004) and 30 h (out of 70-120 h) at 25°C (Clark et al. 2006), and in mature larval length of 2 mm

(out of 12-16 mm) due to dietary differences (Clark et al. 2006; Day and Wallman 2006b; Ireland and Turner 2005; Kaneshrajah and Turner 2004). This means that variation in diet can limit overall precision to 12-43% of the estimated PMI .

Two ways of managing these disparities are obvious: develop substrate-specific developmental models, or be selective about which tissues are sampled for insects. In either case, there is a need to formulate developmental models for human tissues, and to test which animals' tissues are the best substitutes. The effects of diet reinforce the need to record the location of samples on a corpse as a standard procedure (Amendt et al. 2007).

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