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@mail :  cindy.aubernon@univ-lille2.fr      tél. :  0320623511

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Titre de la communication :
Thermoregulation in necrophagous Dipteran larvae: application in forensic entomology.
Auteurs (et leurs adresses) de la communication :
Cindy Aubernon, Valéry Hédouin, Damien Charabidzé Univ.Lille, CHU Lille, EA7367 - UTML - Unité de Taphonomie Médico-Légale, F - 59000
Résumé de la communication :
When a person dies, in wild, his cadaver will be colonized by necrophagous insects. Many species are attracted by decaying corpse, but flies are the most common and numerous. They lay eggs on the cadaver and from these eggs, maggots hatch and nourishing on fleshes. Forensic entomology relies on these insects to date the death in a legal context. A key point for forensic entomologists is that larval growth depends on temperature: maggots grow faster at higher temperatures. Accordingly, understanding the behavior and the physiology of these insects according to temperature is crucial. The aim of my thesis is to highlight the thermal behavior of three species of forensic importance: Lucilia sericata, Calliphora vomitoria and Calliphora vicina
My work can be divided in three parts: 1/ behavior of the maggots in their thermic environment, 2/ effect of sociality (congeners) and 3/ impact of these two points on larval development.
To answer these questions, I designed the Thermograde, a 80cm long food-supplied linear thermal gradient (17°C to 50°C). 80 larvae of one of the three species were placed inside and their location was checked after 19h. The selected temperatures were 33.3±1.52 for L. sericata, 29.61±1.63 for C. vomitoria and 22.43±1.55 for C. vicina. These results suggest a larval behavior for thermal optimization. According to this hypothesis, maggots of each species should move in their environment (i.e. on the corpse), trying to reach location close to their preferential temperature.
To test this postulate, I realized another experiment using a 40cm long food-supplied rearing apparatus with one hot spot at each extremity (25°C and 34°C with an ambient temperature of 20°C). Testing three conditions (spots ignition time), the results show that the larvae were able to select an optimal temperature in their local environment and to move to another place when the environment became less favorable. However, when a group of larvae was located in a healthy area, its moving to a more optimal place was very long or never happened.
These results bring interesting questions regarding the larval growth and physiology. These questions are especially important in the context of forensic entomology for the time of death calculation. Indeed, larval developmental parameters are currently measured using captive larvae reared at a given constant temperature. Such setup prevents any larval thermoregulation, and accordingly do not reflect their actual development under field conditions. Consequently, during my last PhD year, I will realize developmental experiments in a setup allowing larval thermoregulation. With this last experimentation, I will try to demonstrate how the larvae\'s behavior affect their development, and then refine the way forensic entomologist estimate the time of the death.