Les larves de diptères nécrophages en entomologie médico-légale : une histoire de température

L’entomologie médico-légale est l’utilisation des insectes afin de calculer l’intervalle post-mortem (temps écoulé entre la découverte d’un corps et la mort réelle de l’individu). Connaître la biologie, la physiologie et le comportement de ces insectes sur l’écosystème représenté par le cadavre est d’une importance primordiale pour améliorer les expertises entomologiques. C’est sur quoi se focalise l’unité de taphonomie médico-légale, unique équipe de recherche en France experte sur ce sujet

Collective exodigestion favours blow fly colonization and development on fresh carcasses

International audienceNecrophagous flies breeding on carcasses face high selection pressures and therefore provide interesting opportunities to study social adaptations. We postulated that gregariousness in necrophagous blow fly larvae is an adaptive response to the environmental constraints of fresh carcasses. Cooperation is indeed believed to be key to the global success of social species. To test this idea, the development of Lucilia sericata (Diptera: Calliphoridae) larvae growing on low-or high-digestibility food substrate (control or trypsin-added ground beef muscle, respectively) at different larval densities was monitored. Results showed that larvae developed faster and had decreased mortality at high than low larval density. Furthermore, aggregation had no dele-terious effect on the morphological characteristics (e.g. size) of postfeeding larvae and adult flies. We concluded that increased density positively affected population fitness, which is a conclusion consistent with the predictions of the Allee effect. Compared with those fed on regular food, larvae fed on high-digestibility food had reduced mortality and faster development on average. From these results, we postulated that collective exodigestion might be an adaptive response allowing blow flies to colonize fresh carcasses before the arrival of other insects and the multiplication of microbes. This hypothesis is consistent with the idea that cooperation may enable species to expand their niches

Data from: Facing death together: heterospecific aggregations of blowfly larvae evince mutual benefits

Heterospecific aggregations and foraging associations have been observed between different species, from apes to birds to insects. Such associations are hypothesized to result in a mutually beneficial relationship entailing benefits that are not apparent in conspecific groupings. Therefore, the objectives of the present study were to investigate (i) how three blowfly species, namely, Calliphora vicina, C. vomitoria and Lucilia sericata, aggregate according to species, and (ii) if developmental benefits are linked to heterospecific aggregation. For objective (i), larvae of two species were placed between two conspecific aggregates, each with a different species (i.e., a binary choice test). After 20 hours, the positions of all larvae were determined. On average, 98% of the maggots added later settled together on one of the two pre-existing aggregations, demonstrating a collective choice. The aggregation spot with C. vicina was preferred against others, indicating different attractiveness of different species. To relate this behavior to its benefits (objective ii), C. vicina and L. sericata larvae were raised from first instar to adult in con- and heterospecific conditions, and their development time, mortality rates and morphometrics were measured. Thereby, mutual and asymmetric consequences were observed: specifically, there were significant increases in size and survival for L. sericata and faster development for C. vicina in heterospecific groups. These results indicate that the predilection for heterospecific association leads to mutual developmental benefits. This heterospecific aggregation behaviour may be a resource-management strategy of blowflies to face carrion-based selection pressure

Data from: Interspecific shared collective decision-making in two forensically important species

To date, the study of collective behaviour has mainly focused on intraspecific situations: the collective decision-making of mixed-species groups involving interspecific aggregation-segregation has received little attention. Here, we show that, in both conspecific and heterospecific groups, the larvae of two species (Lucilia sericata and Calliphora vomitoria, calliphorid carrion-feeding flies) were able to make a collective choice. In all groups, the choice was made within a few minutes and persisted throughout the experiment period. The monitoring of a focal individual within a group showed that these aggregations were governed by attractive and retentive effects of the group. Furthermore, the similarity observed between the conspecific and heterospecific groups suggested the existence of shared aggregation signals. The group size was found to have a stronger influence than the species of necrophagous larvae. These results should be viewed in relation to the well-known correlation between group size and heat generation. This study provides the first experimental examination of the dynamics of collective decision-making in mixed-species groups of invertebrates, contributing to our understanding of the cooperation-competition phenomenon in animal social groups

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Fatal Overdose of Gamma-hydroxybutyrate Acid After Ingestion of 1,4-Butanediol

International audienceWe report a case of fatal intoxication from 1,4-butanediol (1,4-BD), which was ingested by a young and "naïve" gamma-hydroxybutyrate (GHB) consumer during a party with the co-ingestion of alcohol, cannabis, and methylene-dioxy-methamphetamine. The following drug concentrations were found using gas chromatography coupled with mass spectrometry on autopsy samples and on a cup and a glass found at the scene: 20,350 mg/L (bottle) for 1,4-BD; 1020 mg/L (femoral blood), 3380 mg/L (cardiac blood), 47,280 mg/L (gastric content), and 570 mg/L (vitreous humor) for GHB. The concentration of GHB is difficult to interpret in forensic cases due to the possibility of an endogenous production of GHB. The variable tolerance of the user may also modify the peri- and postmortem GHB concentrations. This case underscores the need to have many different sources of toxicology samples analyzed to avoid the hypothesis of endogenous production of GHB

Mixed-species aggregations in arthropods

This review offers the first synthesis of the research on mixed-species groupings of arthropods and highlights the behavioural and evolutionary questions raised by such behaviour. Mixed-species groups are commonly found in mammals and birds. Such groups are also observed in a large range of arthropod taxa independent of their level of sociality. Several examples are presented to highlight the mechanisms underlying such groupings, particularly the evidence for phylogenetic proximity between members that promotes cross-species recognition. The advantages offered by such aggregates are described and discussed. These advantages can be attributed to the increase in group size and could be identical to those of non-mixed groupings, but competition-cooperation dynamics might also be involved, and such effects may differ between homo- and heterospecific groups. We discuss three extreme cases of interspecific recognition that are likely involved in mixed-species groups as vectors for cross-species aggregation: tolerance behaviour between two social species, one-way mechanism in which one species is attractive to others and two-way mechanism of mutual attraction. As shown in this review, the study of mixed-species groups offers biologists an interesting way to explore the frontiers of cooperation-competition, including the process of sympatric speciation

Extensive Necrotic Purpura in Levamisole-Adulterated Cocaine Abuse - A Case Report

International audienceLevamisole, which is used as an adulterated compound of cocaine, is currently being seen year after year in cocaine intoxication. For a few cases in the last decade, necrotic purpura and neutropenia after levamisole/cocaine intoxication have been described in the medical community. Herein, we present an original case of levamisole intoxication of a 40-year-old woman who smoked heroin and cocaine few during a month. She rapidly presented an extensive necrotic purpura of the nose, cheeks and extremities (lower and upper), and immunologic reactions (positive anti-MPO and anti-HNE). Levamisole was detected on hairs with ultra-high performance liquid chromatography and tandem mass spectrometry. The case reports also a probable cocaine supplier deceit, which bring pure drug for hospital investigation after the intoxication of his client. The intoxicated woman had survived with several skin and chronic pain complications. That case recalls the knowledge about levamisole with a short review of the forensic literature

Detection of hepatitis C virus antibodies and RNA among medicolegal autopsy cases in Northern France

International audienceForensic medical personnel are at risk of exposure to blood-borne viruses including hepatitis C virus (HCV). The aim of this study was to determine prevalence of HCV markers among a cadaver population at the medicolegal institute in Lille. Seventy-seven consecutive cadavers were screened for antibodies to HCV and for HCV RNA. Positive results were confirmed by an immunoblot assay. Fifty-three cadavers had a histopathologic study. Anti-HCV was detected in 13 (16.9%) and accompanied by HCV RNA in 7 (9%) cases. The rate of HCV RNA detection among seropositive cases was 53.8%. Five cases had histopathologic lesions suggestive of hepatitis. This is the first HCV RNA screening in forensic cadavers. The results highlight the high prevalence rate of HCV cases in medicolegal practice in Lille. All forensic specimens should be treated as potentially infectious and universal precautions should be taken