ARBESU Y MIAR Anais
FLORES VILCA Claudia Alejandra
LE ROUZIC Olivier
MEKKI Meriem Sarah
NIETO BOBADILLA Maria Susana
OLIVEIRA PRACA DE ALMEIDA Catarina
SANGARE Lamba Omar
TRAN Ngoc Chau
(EA7367 - Valery HEDOUIN)
Titre de la communication :
Live together on a decaying cadaver: why study the behavior of flies\' offspring?
Auteurs (et leurs adresses) de la communication :
Julien Boulay (1,2), Damien Charabidzé (1) et Valéry Hédouin (1) 1: UTML, Université de Lille 2 - Place de Verdun 59045 Lille cedex 2: Service d\'Ecologie Sociale, Université Libre de Bruxelles - Campus de la Plaine, 1050 Bruxelles
Résumé de la communication :
Forensic entomology is the study of necrophagous insects sampled on human corpses in order to estimate the Post-Mortem Interval (PMI: date of death). The most important species used in this context are Blowflies (Diptera Calliphoridae) and especially their offspring (i.e. larvae or maggots). Maggots feed on decomposition fleshes and their development time is positively correlated with ambient temperature: hotter it gets, faster is maggots\' development. Thus, knowing maggots\' species and thermal development history, PMI estimation can be calculated to help investigators.
Maggots are found on corpses closely aggregated in group gathering thousands of larvae. They feed together at the same place in a frenetic agitation named scramble competition. This maggot excitation creates a local temperature increase: the maggot-mass effect. By producing their own heat, larvae accelerate their development and thus decrease the time spent on the cadaver. No study has focused on mechanisms used by individuals to form, maintain and regulate such large aggregates.
We first showed that maggots\' aggregation did not result from the aggregation of eggs by the adult female but from the active behavior of individuals. Indeed, in a homogeneous nutrient medium, 40 randomly placed larvae of Lucilia sericata (the green bottle fly) formed after 30min a stable aggregate, which progressively increased in number of larvae and persisted in time.
Then, we used a binary choice test to show that maggots were able to make together a choice (collective choice) for one resource site (food patch). Indeed, choice experiments between 2 identical food spots showed that the main part of the 40 larvae used were aggregated on the same spot. This choice was made quickly (<10min) and demonstrated a strong inter-attraction within individuals (self-amplification phenomenon).
Lastly, we demonstrated the existence of a ground signal left by maggots and recognized by congeners. When a larva was placed in a Petri dish where a half was previously marked by five larvae (10min and then removed), the individual spent more time in the half where the signal was deposit than in the half with no signal. Accordingly, we supposed this signal to be one of the aggregation vectors used by larvae.
Our results bring some new knowledge about the maggot behavior to, in fine, improve the techniques used in forensic entomology. Upgrade these techniques will lead to a better estimation of PMI. These results also add to those obtained on different insect species, like cockroaches, in the context of gregariousness, self-organization and origins of animal sociality.
(EA7367 - Valery HEDOUIN)