Increasing Precision in Development-Based Postmortem Interval Estimates: What's Sex Got to Do With It?

Abstract

Forensic entomologists typically use either succession models for postmortem interval (PMI) estimates or development-based models for minimum PMI (PMI(MIN) estimates. Development-based age estimates are calculated with durations of immature stadia and can also include morphological data such as larval size. For developmental data, the first and second instar stages are typically brief with little variation in larval length. The third instar, a much longer stage by comparison, is prone to considerable variation. This variation is, in part, because of the nonlinear growth during the third instar. There is evidence that genetic and environmental factors influence growth curve divergence during this stage. We chose to investigate one genetic factor, sex, as numerous insect species exhibit sex-specific immature growth patterns. The development rate of Lucilia sericata (Meigen) (Diptera: Calliphoridae) males and females is considered here. We previously determined the genome sizes of L. sericata and found significant sexually dimorphic genome sizes. This difference can be exploited to identify larval sex to evaluate male and female immature growth curves. A preliminary development study encompassing the third larval instar was conducted to compare larval lengths for each sex. Results showed length (P < 0.0001) and sex (P < 0.01) were statistically significant predictors of age at two temperatures (30 and 33.5 degrees C), and that total male development was significantly shorter (P < 0.001). These results introduce a new tool, assessment of sex-specific growth, that has the potential to reduce noise in PMI(MIN) estimates when using third instar larvae.

Size at emergence improves accuracy of age estimates in forensically-useful beetle Creophilus maxillosus L. (Staphylinidae)

“…Similar findings were reported for other blowflies, Chrysomya megacephala (Fabricius, 1794) 20 and Cochliomyia macellaria (Fabricius, 1775) 21 . Moreover, differences in development time between females and males were reported for L. sericata 22 , a phorid fly Megaselia scalaris (Loew, 1866) 23 and a staphylinid beetle C. maxillosus 24 . Another source is the precocious egg development, resulting in some eggs from the batch hatching earlier, which occur commonly in sarcophagid flies and less frequently in calliphorid flies 5 , 25 .…”

Post-Colonization Interval Estimates Using Multi-Species Calliphoridae Larval Masses and Spatially Distinct Temperature Data Sets: A Case Study

“…However, there are many biotic and abiotic factors that can influence larval development, thus making it difficult to accurately estimate the initial time of colonization [14]. For example, rain [15], drugs [16,17,18], predation [19], larval sex [20], geographic location and population genetics [21,22], tissue type [23], and bacteria [24] can all significantly affect larval development by either increasing or decreasing the time required for carrion flies to complete their life cycle.…”

Reply: On Throwing out the Baby With the Bathwater: A Reply to Wells

“…WellsÕ letter to the Editor states that the postcolonization Interval (PCI) and period of insect activity (PIA), as deÞned in Tomberlin et al (2011), were esoteric and impracticable concepts. Wells then stated that many researchers were incorrectly using the terms in recent articles and cited our article (Michaud et al 2012) as an example, along with several others (Mondor et al 2012, Berg and Benbow 2013, Bygarski and LeBlanc 2013, Picard et al 2013. Here, we comment on WellsÕ assessment of PIA and PCI and we clarify why a citation to Tomberlin et al (2011) appeared in the introduction of Michaud et al (2012).…”