[Forensic entomology and globalisation].

Abstract

The main aim of Forensic Entomology has always been, and is today, to establish the time of death (P.M.I.: Postmortem Period) or, more exactly, how long a carrion has been exposed in the environment. Most of the invertebrate fauna occurring on corpses consists of insects (mostly Diptera and Coleoptera). They are selectively attracted by the decomposing status of the carrion, and form complex communities or biocenosis within necrophagous or sarcophagous species and their predators, parasites and parasitoids, competing each one another. The rapid and continuos changes of the micro-ecosystem (the body), until its breakdown, does not permit the achievement of a steady state or an equilibrium in the animal communities. These continuous modifications give us the possibility to estimate when (and where) the death has occurred, by the identification of the species feeding on the corpse, the knowledge of their life history, and the length of each stage of their cycle at varying the temperature and the other abiotic factors, external to the carrion ecosystem. The P.M.I. today is still largely based on the tables of faunal succession on human cadavers recognised by Mégin in 1894, with few changes proposed by Authors from other countries. In the last years, however, it happens more and more often, that the natural communities are subverted by the presence of allocton species, which can compete, predate or parasite the most common local sarcophagous insects, modifying, this way, the succession waves and the trophic nets. The immission in the environment of foreign species may be voluntary or casual, but in any case is due to anthropic activities. The voluntary immission happens when some species, employed in the biological struggle against pest or dangerous insects, for pollination of allocton plants, or for other commercial utilities, are beyond man's control and swarm onto the environment; the casual spread is due to the globalisation phenomenon, that distributes the "little organisms" by chance, together with travellers, goods and food items. Together with human migratory flows, raw materials and vegetal foodstuffs travelling from Tropical developing Countries to the North of the world, also many tropical and subtropical insects can be carried out from their original lands. Eurioecious and polyphagous species, and species that evolved mechanisms (as diapausa or hibernation) to get over critical environmental conditions have the highest probability of survival. Saprophagous insects, and flies in particular, evolved such capabilities. The mortality of foreign species due to the difference of temperature and seasonally between tropical and temperate areas was, in the past, the most effective factor limiting the geographic propagation of insects. The ongoing global climate changes induce insect populations, now confined to the tropics, to most likely spread towards middle latitudes, where their specific competitors, predators and parasites, which regulate the population growth, are often absent. The lack of a biological control, the warming up of atmosphere temperature and the fall of the differences among seasons induce a more rapid development and an increased number of generations in new species, that often displace the autocton ones. This phenomenon is much more clear in little and simple ecosystems (such as carrion), mostly occur than in large and complex ecosystems, where many more components, vegetal organisms and phytophagous animals included, are present. To demonstrate how globalisation and climate changes are breaking the geographic barriers, we present some cases in which, during our entomoforensic investigations, performed mainly in North-eastern Italy, Neotropical, African and Asiatic necrophagous flies, beetles and wasp parasitoids have been collected, some of which rare or new for Italy or Paleartic Region. In particular, we report our studies on the american black soldier fly, Hermetia illucens (Diptera: Stratiomyidae), that is showing a heavy competition with the local saprophagous species and is reaching great importance in some man activities and in cattle health.