Determining the season of death from the family composition of insects infesting carrion

Abstract

INTRODUCTIONThe microenvironment to which a carcass is exposed (e.g. shaded or sunlit sites), which affects local air temperature, humidity and rate of dehydration, has a major effect on (i) the rate of decomposition of the carcass, (ii) its attraction as an oviposition/larviposition site for flies, (iii) maggot development and (iv) relative abundance of carrion insects (Shean et al., 1993).Another major factor is the season of the year, which has a crucial influence on weather and on the biotic community of a region, and may also affect both the decomposition process and the composition of the carrion entomofauna (Tomberlin & Adler, 1998).The season is even more important than the time that has elapsed since death in determining the time of colonization of several species of carrion insects, mainly in temperate countries (Anderson, 2010).The seasonality of some carrion arthropods and the different times of colonization of a carcass in different seasons imply that these organisms may be valuable in determining the season of death, which is especially useful when a corpse is discovered long after death occurred (i.e. long PMI cases) (Anderson, 2010). Establishing the season of death can be crucial in determining/eliminating suspects and confirming alibis in the case of murder, accidental death, suicide and even when the death is from natural causes Geberth, 1996). The season of death can also have important implications for legal matters such as inheritance and insurance (Henssge et al., 2002).In spite of its importance, the association between carrion insects and their season of appearance on corpses, and therefore the possibility of predicting the season of death using these organisms, has rarely been investigated (but see, e.g., Archer & Elgar, 2003), and, to the best of our knowledge, has never been statistically modelled.For this reason, it is proposed here to use a statistical approach, a logit-based regression method, to model the season in which death occurred in terms of a function of the area where the carcass was exposed (sunlit or shaded) and the relative abundance of arthropod families found in the carrion. This type of model, which is unusual in the field of forensic entomology, is called a logit model, or specifically in our case, a baseline-category logit model (Agresti, 2002). This type of statistical approach was chosen to build a model able to describe the probability of occurrence of a nominal event (season) as a function of a set of independent covariates. A cross-validation procedure was used to validate the model and assess its accuracy in predicting the season in which death occurred. MATERIAL AND METHODS Study siteThe site was located in an urban forest (22°49´15˝S, 47°04´08˝W) on the campus of the State University of Campinas (UNICAMP) in the municipality of Campinas, São Paulo State, Brazil (approx. 685 m above sea level). The climate of the region is seasonal, with a dry and cool season (winter) occurring from early June to late August, a warm and wet season (summer) from mid-November ...

Spatio-Temporal Dynamics and Preference for Type of Bait in Necrophagous Insects, Particularly Native and Introduced Blow Flies (Diptera: Calliphoridae)

“…Their temporal variations seemed to be randomly determined. Seasonal patterns are forensically important because they may designate species to be used as indicators of seasons (Hwang and Turner 2005) or may deÞne the season of death for corpses with a long PMI (Moretti et al 2011a). If we had used longer sampling periods, seasonal patterns might have appeared.…”

Sarcosaprophagous Diptera assemblages in natural habitats in central Spain: spatial and seasonal changes in composition

“…Such seasonal differences in insect activity and assemblage composition also strongly influence patterns of insect succession and the duration of the stages of decomposition of carrion (Voss et al , 2009; Battán Horenstein et al , 2010). Likewise, the seasonality of sarcosaprophagous insects may be valuable in determining the season of death in cadavers for which the post‐mortem interval is long (Moretti et al , 2011). Thus, forensic entomology studies should be designed to consider temporal variability in the composition and activity of necrophagous insect fauna in order to establish applicable reference data for all seasons (Voss et al , 2009).…”

Spatio-temporal distribution and habitat preference of necrophagous Calliphoridae based on 160 real cases from Switzerland

“…The bottle traps certainly can serve as a basic tool for monitoring of blowflies; however, the attractiveness depends on the type of bait used. Furthermore, such traps can induce biases, because they can be neglected or even avoided by certain species due to their preferred diet [3,[15][16][17] and care should be taken when extrapolating such results to case scenarios [18,19]. For example, C. vomitoria and Protophormia terraenovae are common blowflies, which can be often found on human corpses; however, they might avoid bottle traps, because they prefer a cadaver of a certain size [5,20,21].…”