Discussion on the Validity of Traditional Methods to Calculate by Means of Insects

The debate on global climate change has largely failed to factor in the inherently chaotic, sensitively balanced, and threshold-laden nature of the Earth's climate system and the increased likelihood of abrupt climate change. Current speculation about the future climate and its impact have focused on the IPCC reports (1996a, b, 2001, 2007), which forecast gradual global warming of 1.4°-5.8°C over the current century. During the past century (1965-1995) the greatest extent of warming has been registered during winter in the Northern Hemisphere across Eurasia and inland northern America. At lower latitudes there has been extensive warming across the oceans and, with more seasonal variation, warming across the continents.

It is possible, however, for an abrupt cooling down to occur in selective areas of the world, such as in the North Atlantic regions, caused by the shutdown of the Gulf Stream. Intense cooling has occurred in the mid-latitudes around the central Pacific and in the area between Hudson Bay and Greenland. Environmental conditions are rapidly changing from recent years, induced both by the warming climate and by intense human interaction, such as deforestation, large monocultures, and industrialization. Often the small systematic trends are ignored by nonbiologists, but they may become important in the long term.

These local climate changes would occur quickly, even as the global climate continues to warm slowly. Hansen and colleagues (Hansen and Lebedeff 1987; Hansen et al. 1996) compared global and low-latitude temperature changes, showing that big environmental events, such as El Niño or major volcanic eruptions not only have a heavy impact on local temperatures but have also influenced global climatic fluctuations. Most short-term local changes are not caused by climate change but by land-use change and by natural fluctuations in abundance and distribution of species.

In this scenario it is difficult to predict the trend of animal dispersion. The Earth's warming induces species, especially the ectothermic invertebrates, to shift spontaneously toward lower latitudes and higher altitudes. The capability of adapting to changed conditions allows different native species to survive in their historic areas, but it is possible that they have to partially adapt to their ecological niche, their phenology, or their habitat. The current data allow us to foresee that some species will occupy new areas and others will become niche-species or extinct. Along with other insects, many fly species are saprophagous or preferentially necrophagous as adults and particularly as larvae, feeding on all decaying matter.

Most of these species are not only generalist in their feeding behavior but also in suffering temperature changes and thermal shocks by means of diapauses. In this way, for example, the tropical soldier fly, Hermetia illucens, has survived in the southern temperate regions of Europe, modifying its diapause length and its voltinism. In many years, thanks also to increasing temperatures, this alien species has become able to shift northward and to higher altitudes. Other saprophagous or necrophilous insects, strictly linked to humans and human food or waste, can live in the cities of cold lands when they could not survive in their surroundings. A strictly connected example may also be the presence of termites in the houses of Venice and Padova, which until now were only found in central and southern Italy. This finding demonstrates that medium to large cities are spots of constant warmth. Following Hansen and Lebedeff (1987), cities with more than 100,000 inhabitants have modified the regional temperature by 0.1°C or more. Karl and Williams (1987) estimated that global warming during the past century may be reduced by 0.1°C if these cities are excluded, and that the total urban effect on the current global climate is 0.1°-0.2°C on average.

The climatic variations, in terms of both temperatures and weather, directly modify biotopes and vegetation arrangement, affecting the composition of communities. The necrophilous arthropods, such as the other organisms, suffer a selective pressure to adapt to the new conditions or, if they are able, to shift toward new, more consistent areas. This last choice is evident for many species, which have rapidly expanded the cool margins of their geographical ranges.

This is, for example, the case with the blowfly Chrysomya albiceps, as reported by Grassberger et al. (2003). It was once abundant in the Austral Hemisphere and southern Europe but has now migrated northward to central Europe; or Megaselia scalaris, a species of tropical climates and of the Mediterranean Basin, found in Belgium by Dewaele and Leclercq (2002). The continuity of the increase in the population's ranges leads us to suppose a spontaneous migration. Often the presence of new species dramatically affects the native populations, being their predators and/or competitors, such as C. albipes versus Lucilia sericata (Grassberger et al. 2001) and H. illucens (Turchetto et al. 2001) or more resistant to pesticides (Turchetto 2000).

Taking into account all the considerations reported above, the classic forensic indications about the methods in forensic entomology must be critically revised. Without entering into the subject of the rate of the body's degradation and tissue decay, which can also in some way be affected and accelerated by the warming climate, we restrict our attention only to cadaveric fauna. The eight invasion waves of arthropods proposed by Megnin in 1894 have been reevaluated many times with small variations, regarding overall the number of stages of carcass decomposition. Megnin, however, lived at the end of the Little Ice Age, when the global temperature was 1°C lower than at present; moreover, the local temperatures were somewhat lower, and precipitation was more abundant. Few concentrated built-up areas constituted the landscape, as in most parts of Europe, whereas today the land and woods have been overtaken by the spread of cities and industries. The consequences of human activity such as energy emitted as heat and the transformation of natural environments in cultivated fields (often the largest monocultures) along with deforestation have added to the impact of natural events, such as desertification, the changed level of precipitation (much lesser in some regions or concentrated in a few days throughout the year), the alteration of monsoons, and the shift and higher force of hurricanes (shifted northward, arriving through the Atlantic in northwestern Europe and England), forcing the entire fauna to change. The trend of rising temperatures was confirmed by the most recent data of 2006, as shown in Fig. 15.13 for the past 30 years. Following the NOAA report in 2006 based on preliminary data, the globally averaged combined land and sea surface temperature was the warmest on record for December 2006 and the fifth warmest for January-December. Temperatures were above average in the United States, Europe, southern Asia, central Russia, and most of South America; and cooler-than-average conditions occurred in the Middle East region. Precipitation during December 2006 was above average in Scandinavia, England, Japan, central United States, south-eastern Africa, and most of South America; and drier than average conditions were observed in the eastern United States, central Europe, eastern Australia, and southern India. December 2006 was the warmest since global surface records began in 1880 for combined global land and ocean surface temperatures. December land surface temperatures were the fourth warmest on record, and ocean surface temperatures were the second warmest in the 127-year record, behind only 1997, during which the very strong 1997/1998 El Niño event was developing. ENSO conditions persisted in a warm phase (El Niño) during December.

In light of all these considerations, new tables of carrion decay and arthropod succession must be formulated for more precise evaluation of the PMI. We suggest tables on a regional scale that are revised moreover, at frequent time intervals, so environmental and climatic parameters can be considered constant. The astronomic division of the year into spring, summer, autumn, and winter are not given to precise data and would be better substituted with the calendar months including mean, maximum and minimum temperatures. This proposal, which takes into account the selective pressures of climate change on the necrophagous insects, could foster

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Fig. 15.13 Global mid-tropospheric temperature. Radiosonde measurements indicate that for the January-December period temperatures in the mid-troposphere (approximately 2-6 miles above the Earth's surface) were 0.56°C above average, creating the third warmest January-December since global measurements began in 1958 (data were obtained from http://www.ncdc.noaa.gov/oa/ climate/research/2006/dec/global.html/)

agreement between the different methods of working of forensic entomologists strictly linked to the classic tables of faunal succession and those believing that every death find is a case apart.

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