Les cadavres sont des écosystèmes fugaces où la vie explose. Une sorte de vie qui n'inspire à... more Les cadavres sont des écosystèmes fugaces où la vie explose. Une sorte de vie qui n'inspire à la plupart d'entre nous que le dégoût. Pourtant, s'ils sont parfois vecteurs d'infections graves, les insectes nécrophages sont aussi d'utiles "éboueurs" susceptibles de devenir aussi les précieux auxiliaires de la justice et, pour certains, de la médecine. U n cadavre constitue une ressource énergétique importante : de nombreux insectes nécrophages vont donc l'exploiter et y proliférer très rapidement. Il s'agit cependant d'un écosystème bien particulier, caractérisé notamment par sa courte durée d'existence. Les insectes qui exploitent cette ressource ponctuelle et éphémère présentent des adaptations particulières. Il s'agit d'espèces fréquentes et ayant une large répartition géographique. Les adultes ne sont pas inféodés à un milieu particulier et peuvent donc se déplacer facilement. Ils présentent un système olfactif particulièrement...
La mesure de la température corporelle est un des principaux critères de détermination de l’inter... more La mesure de la température corporelle est un des principaux critères de détermination de l’intervalle post-mortem (IPM). Après le décès, la température du corps s’aligne progressivement sur la température ambiante : cette évolution est régie par des lois de transferts thermiques connues. Un certain nombre de méthodes, parmi lesquelles le nomogramme de Henssge, se basent sur cette relation afin d’estimer l’IPM. Cependant, lorsque le corps se trouve à température ambiante variable, aucune méthode ne permet de prédire l’évolution de sa température interne. Ce travail présente les résultats d’un modèle permettant de simuler l’évolution de la température rectale d’un corps lorsque la température de son environnement varie. Les données obtenues grâce à ce modèle ont été comparées aux estimations d’IPM obtenues grâce au nomogramme de Henssge afin de tester la validité de celui-ci dans le cas d’un corps soumis à une température ambiante variable. Les résultats indiquent que le nomogramme de Henssge (et plus généralement les méthodes basées sur les données de décroissance thermique) ne peut être utilisé lorsque la température ambiante varie, même faiblement (4 °C sur 24 heures).The measure of the rectal temperature is one of the main post-mortem interval (PMI) estimation tool. After the death, the body temperature decreases until reaching the ambient temperature. This evolution is well known and governed by heat transfer laws. Several methods, as the Henssge's nomogram, use this thermal indicator to estimate the PMI. However, when the body environment temperature varies, no method allows to predict the evolution of the internal temperature. This work presents the results of a computer model allowing the simulation of human body thermal inertia, and evolution of the post-mortem rectal temperature in response to variable ambient temperatures. In order to test Henssge's nomogram validity in case of body at variable ambient temperature, model data were compared to PMI estimation obtained using the nomogram. Results indicate that the rectal temperature can not be use if the environment temperature vary, even if these variations have low amplitude (4 °C in 24 h).
ABSTRACT Aggregation vectors are well known for some arthropod species, but stayed unsolved for m... more ABSTRACT Aggregation vectors are well known for some arthropod species, but stayed unsolved for many others. This study aims to characterize the effect of different signals (e.g. chemical, tactile) on the gregarious behavior of carrion fly larvae (Lucilia sericata) (Diptera: Calliphoridae). For such experiments, the age of individuals and their satiety must be considered. Indeed, preliminary observations show that the behavior of larvae depends on both instar and food requirement. First results also focused our research on the likely use of an odor as an aggregation vector. Subsequently, different odors have been tested using a video-tracking system. Results indicates that individuals are significantly attracted by feeding-places extract (extract from meat where larvae fed & grown). This attraction is significantly higher than the one observed on control fresh meat areas, demonstrating existence of a contact or odor-mediated gregarious signal. Other odor choice tests, including direct odor deposit by conspecifics, have subsequently been analyzed and will be discussed. Furthermore, observations confirm the significance of the thigmotactic behavior. Tactile stimuli may therefore also be involved in the formation of aggregates. Additional binary test, using two possible aggregation sites, will be performed. Results of these experiments and conclusions of this study will be discussed in the context of self-organization and gregariousness.
Necrodes littoralis (Linnaeus, 1758) (Coleoptera: Silphidae), also known as the &... more Necrodes littoralis (Linnaeus, 1758) (Coleoptera: Silphidae), also known as the "shore sexton beetle," is a common silphid beetle that visits and breeds on large vertebrate cadavers. This study describes, for the first time, the involvement of N. littoralis on human corpses based on a large dataset of 154 French forensic cases. Various parameters regarding corpse location, decomposition stages, and entomofauna were extracted from each file. Compared to all of the forensic entomology cases analyzed between 1990 and 2013 (1028), N. littoralis was observed, on average, in one case out of eight; most of these cases occurred during spring and summer (73.5 %). More than 90 % of the cases were located outdoors, especially in woodlands, bushes, and fields. The decomposition stage of the corpse varied among cases, with more than 50 % in the advanced decomposition stage, 36 % in the early decomposition stage, and less than 10 % in the fresh, mummified, or skeletonized stages. Regarding other necrophagous species sampled with N. littoralis, Calliphorid flies were found in 94 % of the cases and Fanniidae/Muscidae in 65 % of the cases. Chrysomya albiceps, a heliophilic species mostly located in the Mediterranean area, was present in 34 % of the cases (only 20 % in the whole dataset). The most common coleopteran species were Necrobia spp. (Coleoptera: Cleridae) and Creophilus maxillosus (Coleoptera: Staphylinidae); these beetles were observed in 27 % of the cases. The over-representation of these species is likely due to similar requirements regarding the climate and decomposition stage. As N. littoralis is frequently observed and tends to become more common, we conclude that the developmental data for this species would be a precious tool for forensic entomologists in Europe.
It is well known that Blowflies larvae (Diptera Calliphoridae) development time is mainly control... more It is well known that Blowflies larvae (Diptera Calliphoridae) development time is mainly controlled by local temperature. Accordingly, it has been experimentally demonstrated that each species has an optimal development temperature, characterized by a short development time and a high survival rate. Furthermore, in recent study, it has been showed that larvae move inside masses to select preferential thermic areas. Then, temperature felt by larvae during their development on a corpse may be behaviorally selected. If so, use of ambient temperature or maximum maggot-mass temperature to estimate development time of larvae on a corpse would be meaningless. In a first experiment we designed the ThermoGrad, a 80cm long thermal gradient setup, to determine specific preferential temperatures. The temperature gradient was set with linear increase from 15°C to 45°C. This experiment was performed on 3 different species: Lucilia sericata (N=10), Calliphora vomitoria (N=10) and Calliphora vicin...
Les cadavres sont des écosystèmes fugaces où la vie explose. Une sorte de vie qui n'inspire à... more Les cadavres sont des écosystèmes fugaces où la vie explose. Une sorte de vie qui n'inspire à la plupart d'entre nous que le dégoût. Pourtant, s'ils sont parfois vecteurs d'infections graves, les insectes nécrophages sont aussi d'utiles "éboueurs" susceptibles de devenir aussi les précieux auxiliaires de la justice et, pour certains, de la médecine. U n cadavre constitue une ressource énergétique importante : de nombreux insectes nécrophages vont donc l'exploiter et y proliférer très rapidement. Il s'agit cependant d'un écosystème bien particulier, caractérisé notamment par sa courte durée d'existence. Les insectes qui exploitent cette ressource ponctuelle et éphémère présentent des adaptations particulières. Il s'agit d'espèces fréquentes et ayant une large répartition géographique. Les adultes ne sont pas inféodés à un milieu particulier et peuvent donc se déplacer facilement. Ils présentent un système olfactif particulièrement...
La mesure de la température corporelle est un des principaux critères de détermination de l’inter... more La mesure de la température corporelle est un des principaux critères de détermination de l’intervalle post-mortem (IPM). Après le décès, la température du corps s’aligne progressivement sur la température ambiante : cette évolution est régie par des lois de transferts thermiques connues. Un certain nombre de méthodes, parmi lesquelles le nomogramme de Henssge, se basent sur cette relation afin d’estimer l’IPM. Cependant, lorsque le corps se trouve à température ambiante variable, aucune méthode ne permet de prédire l’évolution de sa température interne. Ce travail présente les résultats d’un modèle permettant de simuler l’évolution de la température rectale d’un corps lorsque la température de son environnement varie. Les données obtenues grâce à ce modèle ont été comparées aux estimations d’IPM obtenues grâce au nomogramme de Henssge afin de tester la validité de celui-ci dans le cas d’un corps soumis à une température ambiante variable. Les résultats indiquent que le nomogramme de Henssge (et plus généralement les méthodes basées sur les données de décroissance thermique) ne peut être utilisé lorsque la température ambiante varie, même faiblement (4 °C sur 24 heures).The measure of the rectal temperature is one of the main post-mortem interval (PMI) estimation tool. After the death, the body temperature decreases until reaching the ambient temperature. This evolution is well known and governed by heat transfer laws. Several methods, as the Henssge's nomogram, use this thermal indicator to estimate the PMI. However, when the body environment temperature varies, no method allows to predict the evolution of the internal temperature. This work presents the results of a computer model allowing the simulation of human body thermal inertia, and evolution of the post-mortem rectal temperature in response to variable ambient temperatures. In order to test Henssge's nomogram validity in case of body at variable ambient temperature, model data were compared to PMI estimation obtained using the nomogram. Results indicate that the rectal temperature can not be use if the environment temperature vary, even if these variations have low amplitude (4 °C in 24 h).
ABSTRACT Aggregation vectors are well known for some arthropod species, but stayed unsolved for m... more ABSTRACT Aggregation vectors are well known for some arthropod species, but stayed unsolved for many others. This study aims to characterize the effect of different signals (e.g. chemical, tactile) on the gregarious behavior of carrion fly larvae (Lucilia sericata) (Diptera: Calliphoridae). For such experiments, the age of individuals and their satiety must be considered. Indeed, preliminary observations show that the behavior of larvae depends on both instar and food requirement. First results also focused our research on the likely use of an odor as an aggregation vector. Subsequently, different odors have been tested using a video-tracking system. Results indicates that individuals are significantly attracted by feeding-places extract (extract from meat where larvae fed & grown). This attraction is significantly higher than the one observed on control fresh meat areas, demonstrating existence of a contact or odor-mediated gregarious signal. Other odor choice tests, including direct odor deposit by conspecifics, have subsequently been analyzed and will be discussed. Furthermore, observations confirm the significance of the thigmotactic behavior. Tactile stimuli may therefore also be involved in the formation of aggregates. Additional binary test, using two possible aggregation sites, will be performed. Results of these experiments and conclusions of this study will be discussed in the context of self-organization and gregariousness.
Necrodes littoralis (Linnaeus, 1758) (Coleoptera: Silphidae), also known as the &... more Necrodes littoralis (Linnaeus, 1758) (Coleoptera: Silphidae), also known as the "shore sexton beetle," is a common silphid beetle that visits and breeds on large vertebrate cadavers. This study describes, for the first time, the involvement of N. littoralis on human corpses based on a large dataset of 154 French forensic cases. Various parameters regarding corpse location, decomposition stages, and entomofauna were extracted from each file. Compared to all of the forensic entomology cases analyzed between 1990 and 2013 (1028), N. littoralis was observed, on average, in one case out of eight; most of these cases occurred during spring and summer (73.5 %). More than 90 % of the cases were located outdoors, especially in woodlands, bushes, and fields. The decomposition stage of the corpse varied among cases, with more than 50 % in the advanced decomposition stage, 36 % in the early decomposition stage, and less than 10 % in the fresh, mummified, or skeletonized stages. Regarding other necrophagous species sampled with N. littoralis, Calliphorid flies were found in 94 % of the cases and Fanniidae/Muscidae in 65 % of the cases. Chrysomya albiceps, a heliophilic species mostly located in the Mediterranean area, was present in 34 % of the cases (only 20 % in the whole dataset). The most common coleopteran species were Necrobia spp. (Coleoptera: Cleridae) and Creophilus maxillosus (Coleoptera: Staphylinidae); these beetles were observed in 27 % of the cases. The over-representation of these species is likely due to similar requirements regarding the climate and decomposition stage. As N. littoralis is frequently observed and tends to become more common, we conclude that the developmental data for this species would be a precious tool for forensic entomologists in Europe.
It is well known that Blowflies larvae (Diptera Calliphoridae) development time is mainly control... more It is well known that Blowflies larvae (Diptera Calliphoridae) development time is mainly controlled by local temperature. Accordingly, it has been experimentally demonstrated that each species has an optimal development temperature, characterized by a short development time and a high survival rate. Furthermore, in recent study, it has been showed that larvae move inside masses to select preferential thermic areas. Then, temperature felt by larvae during their development on a corpse may be behaviorally selected. If so, use of ambient temperature or maximum maggot-mass temperature to estimate development time of larvae on a corpse would be meaningless. In a first experiment we designed the ThermoGrad, a 80cm long thermal gradient setup, to determine specific preferential temperatures. The temperature gradient was set with linear increase from 15°C to 45°C. This experiment was performed on 3 different species: Lucilia sericata (N=10), Calliphora vomitoria (N=10) and Calliphora vicin...
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