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Early colonisation of urban indoor carcasses by blow flies (Diptera: Calliphoridae): An experimental study from central SpainDue to their ubiquity and synanthropy, blow flies (Diptera: Calliphoridae) are generally the first colonisers of cadavers and, therefore, frequently used to estimate a minimum post-mortem interval (minPMI). Whereas in outdoor situations blow flies are expected to locate and colonise exposed cadavers within hours or even minutes after death, it is usually assumed that the colonisation of a cadaver indoors might be delayed for an uncertain period of time. This uncertainty severely limits the informativity of minPMI estimates based on entomological evidence. Moreover, these limitations are emphasised by the lack of experimental data on insect colonisation of indoor carrion and by the fact that most of the forensic cases involving entomological evidence have been reported to occur indoors. In this study we investigate the early colonisation of pig carcasses placed indoors in a building located in the centre of an urban environment in central Spain. Three carcasses were placed in three equal rooms with a window half opened during five experimental trials: summer 2013, autumn 2013, winter 2014, spring 2014 and summer 2014. The species composition and their contribution to the carrion colonisation differed among seasons. Calliphora vicina Robineau–Desvoidy was the sole coloniser of carcasses in winter and colonised the carcasses within the first 24–48 h in every season, although Lucilia sericata (Meigen) was the first coloniser of most summer carcasses. On the other hand, Calliphora vomitoria (L.) and Chrysomya albiceps (Wiedemann) colonised the carcasses significantly later in spring and in spring and summer, respectively, with a delay of several days. In autumn, however, there were no significant differences in the colonisation times by C. vicina, L. sericata and Ch. albiceps. C. vicina and L. sericata showed a clear preference for ovipositing in the natural orifices of the carcasses, whereas Ch. albiceps oviposited more frequently on the trunk and legs.
Estimating crime scene temperatures from nearby meteorological station dataThe importance of temperature data in minimum postmortem interval (minPMI) estimations in criminal investigations is well known. To maximise the accuracy of minPMI estimations, it is imperative to investigate the different components involved in temperature modelling, such as the duration of temperature data logger placement at the crime scene and choice of nearest weather station to compare the crime scene data to. Currently, there is no standardised practice on how long to leave the temperature data logger at the crime scene and the effects of varying logger duration are little known. The choice of the nearest weather station is usually made based on availability and accessibility of data from weather stations in the crime scene vicinity. However, there are no guidelines on what to look for to maximise the comparability of weather station and crime scene temperatures. Linear regression analysis of scene data with data from weather stations with varying time intervals, distances, altitudes and microclimates showed the greatest goodness of fit (R2), i.e. the highest compatibility between datasets, after 4–10 days. However, there was no significant improvement in estimation of crime scene temperatures beyond a 5-day regression period. The smaller the distance between scene and weather station and the higher the similarity in environment, such as altitude and geographical area, resulted in greater compatibility between datasets. Overall, the study demonstrated the complexity of choosing the most comparable weather station to the crime scene, especially because of a high variation in seasonal temperature and numerous influencing factors such as geographical location, urban ‘heat island effect’ and microclimates. Despite subtle differences, for both urban and rural areas an optimal data fit was generally reached after about five consecutive days within a radius of up to 30 km of the ‘crime scene’. With increasing distance and differing altitudes, a lower overall data fit was observed, and a diminishing increase in R2 values was reached after 4–10 consecutive days. These results demonstrate the need for caution regarding distances and climate differences when using weather station data for retrospective regression analyses for estimating temperatures at crime scenes. However, the estimates of scene temperatures from regression analysis were better than simply using the temperatures from the nearest weather station. This study provides recommendations for data logging duration of operation, and a baseline for further research into producing standard guidelines for increasing the accuracy of minPMI estimations and, ultimately, greater robustness of forensic entomology evidence in court.