**2. Necrophagous Diptera: Primary forensic indicator species**

Before turning our full attention to parasitic wasps for the remainder of this chapter, it is worth briefly examining the features of necrophagous flies that make them especially well suited for use in death investigations. This in turn will serve as a foundation for making comparisons to the traits of parasitic Hymenoptera associated with carrion communities. Certain species of flies are invaluable for estimating a portion of the post-mortem interval and also in assessing whether a body has been moved. The first key characteristic was already addressed, and it lies in the need of adult females to find protein for provisioning eggs. In reality, this is true of only some species, those that are anautogenous. Such flies tend to be first wave colonizers, often arriving shortly after death. Thus, the timing of oviposition often closely approximates the perimortem window after the agonal period. Several species of calliphorids are anautogenous, early colonizers. Many autogenous calliphorids species are also early colonizers, motivated to forage for oviposition sites that maximize female fitness. This essentially means locating carrion while protein resources for progeny development are still abundant. The latter comment leads to a second feature of necrophagous flies: faunal succession is relatively predictable for specific stages of physical decomposition [1]. Really the same is true for nondipteran insects with the exception that the period of insect activity is often more broad than for flies serving as primary forensic indicator species. What this also means is that the absence of particular species can convey relevant information as well. For example, lack of first wave or early colonizers suggests that the body was not accessible for a set period of time, or that environmental conditions were not favorable for insect activity until a later stage of decom‐ position. The third key characteristic is that necrophagous fly larvae feed exclusively on the corpse, thereby linking immature development to the post-mortem existence of the deceased, which includes the habitat and environment where the remains are located [14]. A linkage to the environment is also a key feature of flies in that they are poikilothermic and derive thermal energy from the local microenvironment for development. By understanding the duration of development under a range of temperatures and environmental conditions, calculations can be made of how long a fly larva has been present on a corpse [15]. This, in turn, permits an estimation of the minimum length of time that the remains must have been available for colonization for the fly of interest to reach the stage of development found at the time of body discovery. What this means is that larval development of flies can be used to calculate the minimum post-mortem interval [16]. Such predictions based on environmental conditions also necessitate that the stage of fly development can be determined, a process that is aided by the fact that flies exhibit determinant development, meaning that there are a fixed number of larval instars regardless of changes in abiotic and biotic factors in the environment [17]. Other insects that inhabit carrion generally are not exclusively saprophagous/necrophagous such as certain species of flies and/or experience indeterminant development, and thus offer more limited use in criminal investigations.

Despite the value of necrophagous flies to medicocriminal entomology, there are shortcomings or limitations to their utility in death investigations. The most obvious is that after third instar larvae complete feeding, they disperse from the corpse [18]. This does not end the usefulness of flies, but it does reduce their value as physical evidence. Diminished value is due in part to the fact that the larvae are no longer feeding and thus a direct linkage to the corpse has ceased. The length of the wandering stage also can be highly variable between species, decreasing the precision in estimating a minimum PMI based on any developmental stage post-feeding [19, 20]. As well, recovery of dispersed flies from the crime scene can be challenging dependent on body location, soil type, and fly species, the latter of which show a great deal of variability in terms of distance dispersed from the remains [18]. The most important factors limiting the value of flies as physical evidence are those that impact the rate of immature development [1, 15]. The key to this statement is that use of fly development in predicting the PMI is based on the underlying assumption that a linear relationship exists between the rate of larval devel‐ opment and ambient temperatures. Obviously any factor that influences growth independent of temperature violates this assumption and thus diminishes the value of flies, and most importantly, leads to less precise estimations of the PMI. Such factors as maggot mass temperatures, overcrowding, competition, cannibalism/predation among and between fly species, and nutritional quality of corpse tissues are just some of the influences known to alter the rate of fly development. Each of these factors is highly variable, reflecting the unique conditions of independent death events, which in turn makes them extremely challenging to incorporate into fly growth models. Thus, there is a need to compliment the use of necropha‐ gous Diptera with other ecological evidence collected from crime scenes, such as in the form of alternative forensic indicator species. One such group is the parasitic Hymenoptera, which possess life history traits that overcome some of the limitations encountered with fly larvae.

**2. Necrophagous Diptera: Primary forensic indicator species**

70 Forensic Analysis - From Death to Justice

in criminal investigations.

Before turning our full attention to parasitic wasps for the remainder of this chapter, it is worth briefly examining the features of necrophagous flies that make them especially well suited for use in death investigations. This in turn will serve as a foundation for making comparisons to the traits of parasitic Hymenoptera associated with carrion communities. Certain species of flies are invaluable for estimating a portion of the post-mortem interval and also in assessing whether a body has been moved. The first key characteristic was already addressed, and it lies in the need of adult females to find protein for provisioning eggs. In reality, this is true of only some species, those that are anautogenous. Such flies tend to be first wave colonizers, often arriving shortly after death. Thus, the timing of oviposition often closely approximates the perimortem window after the agonal period. Several species of calliphorids are anautogenous, early colonizers. Many autogenous calliphorids species are also early colonizers, motivated to forage for oviposition sites that maximize female fitness. This essentially means locating carrion while protein resources for progeny development are still abundant. The latter comment leads to a second feature of necrophagous flies: faunal succession is relatively predictable for specific stages of physical decomposition [1]. Really the same is true for nondipteran insects with the exception that the period of insect activity is often more broad than for flies serving as primary forensic indicator species. What this also means is that the absence of particular species can convey relevant information as well. For example, lack of first wave or early colonizers suggests that the body was not accessible for a set period of time, or that environmental conditions were not favorable for insect activity until a later stage of decom‐ position. The third key characteristic is that necrophagous fly larvae feed exclusively on the corpse, thereby linking immature development to the post-mortem existence of the deceased, which includes the habitat and environment where the remains are located [14]. A linkage to the environment is also a key feature of flies in that they are poikilothermic and derive thermal energy from the local microenvironment for development. By understanding the duration of development under a range of temperatures and environmental conditions, calculations can be made of how long a fly larva has been present on a corpse [15]. This, in turn, permits an estimation of the minimum length of time that the remains must have been available for colonization for the fly of interest to reach the stage of development found at the time of body discovery. What this means is that larval development of flies can be used to calculate the minimum post-mortem interval [16]. Such predictions based on environmental conditions also necessitate that the stage of fly development can be determined, a process that is aided by the fact that flies exhibit determinant development, meaning that there are a fixed number of larval instars regardless of changes in abiotic and biotic factors in the environment [17]. Other insects that inhabit carrion generally are not exclusively saprophagous/necrophagous such as certain species of flies and/or experience indeterminant development, and thus offer more limited use

Despite the value of necrophagous flies to medicocriminal entomology, there are shortcomings or limitations to their utility in death investigations. The most obvious is that after third instar larvae complete feeding, they disperse from the corpse [18]. This does not end the usefulness of flies, but it does reduce their value as physical evidence. Diminished value is due in part to
