Download The corpse is a silent witness who never lies.

“The corpse is a silent witness who never lies.”
-Anonymou
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Forensic entomology, by definition, refers to the association of insects and other
arthropods with any legal matter though many people prefer to use this term only as
related to the insects associated with a corpse at a murder scene. Application of
entomological knowledge during crime investigations requires detailed information about
the life history, habits, immature stages, geographical distribution, taxonomy etc.
regarding the insects which can be potentially important as forensic indicators. Workers
around the globe have laid stress on the importance of entomological evidence and its
implications in criminal cases and research papers have continued to pour in dealing with
various aspects of the subject. Moreover, seven books dealing exclusively with forensic
entomology have been published so far.
1. “A Manual of Forensic Entomology” by Smith (1986).
2. “Entomology and Death: A Procedural Guide” by Catts and Haskell (1990).
3. “Forensic Entomology- The Utility of Arthropods in Legal Investigations” by Byrd
and Castner (2000).
4. “A Fly For the Prosecution: How Insect Evidence Helps Solve Crimes” by Goff
(2000).
5. “Entomology and the Law: Flies as Forensic Indicators" by Greenberg and Kunich
(2002).
6. “Maggots, Murder and Men” by Erzinclioglu (2002).
7. “Forensic Entomology: An Introduction” by Gennard (2007).
8. “Current Concepts in Forensic Entomology” by Amendt, Goff, Campobasso and
Grassberger (2010).
Overall, there has been a sizeable representation of several hundred research papers
dealing with various aspects of forensic entomology. The prestigious Journal, Forensic
Science International, published a special issue on forensic entomology in 2002 which
included research papers by many renowned forensic entomologists of the world.
Similarly, a full volume was devoted to this branch of science in Anil Aggarwal´s
Internet Journal of Forensic Medicine and Toxicology in 2004.
Due to non-availability of human bodies for decomposition studies, a wide array
of different animal carcasses has been used to simulate humans by various workers from
time to time. In most of these studies, insect fauna mainly comprises of Order Diptera
(blow flies and flesh flies), Coleoptera (Silphidae, Staphylinidae and Dermestidae) and
Hymenoptera.
Man has been able to associate insects (mainly flies) with carrion (animal or
human) for thousands of years. For example, in Homer’s The Illiad, the character
Achilles worries about the dead body of his friend, Patrokis, fearing that flies will “breed
worms” and “make the body foul” (Homer, The Illiad, Book 19). The Illiad is commonly
dated back to the 9th or 8th century B.C. The first reference to blow flies was given more
than 3600 years ago in the Har-ra-Hubulla, a collection of cuneiform writings on clay. It
is one of the oldest known book in zoology and first mentions the “green” fly and the
“blue” fly (Greenberg and Kunich, 2002). Some 2500 years ago, the Egyptians embalmed
deceased individuals in order to protect them from insects and decay. Larvae are even
referenced in the Book of the Dead, (Allen, 1960) Chapter 154: “That my body will not
become prey to larvae”.
It wasn’t until the 13th century A. D. that insects associated with a decomposing
tissue was used to solve a crime. In 1247, Sung Tz’u, published The Washing Away of
Wrongs, a training manual for death scene investigators. In this manual, he tells the story
of a murder by slashing that occurred in a rural village of farmers. The wound on the
victim appeared to have been made by a sickle, so the investigator had all the men of the
village assemble in a line with their sickles lying on the ground before them. The guilty
individual was identified when the investigator noticed a cluster of flies surrounding his
sickle. Although the weapon had been wiped clean, there was enough blood and other
tissue residue left on the blade to attract dozens of flies, thus identifying the suspect
(McKnight, 1981).
At the beginning of the nineteenth century, Mende (1829) compiled a list of
necrophagous insects, including flies and beetles as well as other taxa. Krahmer (1857)
described the opportunities and problems associated with using insects for the estimation
of the minimum postmortem interval (PMI), many of which are still relevant today.
The first application of forensic entomology in a French courtroom, in 1850, can
be viewed as a breakthrough for this discipline (Bergeret, 1855). Skeletonised remains of
a child were found behind a chimney by workmen during redecoration and insect
evidence was accepted as proof that the current occupants of the building could not have
been the murderers. At that time, forensic examiners had only a poor understanding of
insect biology and their knowledge was based largely on casual observations. Although
Weismann (1864) published development data for two necrophagous fly species, it was
not widely noted by the forensic community. Yovanovich (1888) and Megnin (1894)
were the first forensic examiners who attempted to evaluate insect succession on corpses,
properly establishing the science of forensic entomology. The earliest study on this
subject in India is believed to be by Mackenzie in Calcutta (Indian Medical Gazette,
1889) where he made observations on dead bodies about the times of appearance of eggs
and larvae though not much record is available about this study in the contemporary
literature.
Johnston and Villeneuve (1897), Leclercq and Leclercq (1948), Leclercq (1968,
1969, 1983, 1997), Nuorteva (1959a, 1959b) and Nuorteva et al. (1974) were among the
first to use forensic entomology for the determination of the minimum postmortem
interval. Researchers like Reiter and Wolleneck (1982, 1983) and Reiter (1984) hinted
about the forensic importance of the common necrophagous fly Calliphora vicina while
studying its development. Many others like Marchenko (1980, 1988, 2001), Erzinclioglu
(1983a, 1985a, 1986, 2003), Rodriguez and Bass (1983), Vinogradova and Marchenko
(1984), Greenberg (1985), Goff et al. (1989), Nishida et al. (1986), Lord et al.
(1986),Turner (1987), Introna et al.(1989) and Goff (1991a) have laid stress on the
importance of insect evidence during forensic investigations. Now, at the beginning of
the 21st century, forensic entomology has been accepted in many countries as an
important forensic tool (Keh, 1985 ; Goff, 1991a, 1991b; Greenberg, 1991; Catts and
Goff, 1992; Morris, 1994; Anderson, 1996; Benecke,1996 a, b; Introna et al., 1998;
Benecke,1998 a,b; Benecke,1999; Bourel et al., 1999; Malgorn and Coquoz 1999; Oliva
et al., 1995; Campobasso and Introna 2001; Campobasso et al., 2001; Wolff et al., 2001;
Lord and Goff, 2003; Benecke, 2004; Amendt, 2004 a, b). Benecke (2001 b) and
Grassberger (2004) described fundamentals and a brief history of forensic entomology.
Singh et al. (1999), Anderson (2001a) and Klotzbach et al. (2004) have discussed the
development of this science in India, British Columbia (Canada) and German speaking
countries, respectively.
In order to review the voluminous available literature in a meaningful way, it has
been considered better to discuss the relevant papers under different headings.
Insect fauna of corpse
Hough (1897) studied the fauna of dead bodies with special reference to Diptera
and also compared the insect fauna of America with that of Europe. Motter (1898)
studied 150 disinterments where dates of original interments were known to him and
provided a detailed list of the fauna found on the buried bodies. Fuller (1934) also studied
the insect inhabitants of carrion. According to Chapman and Sankey (1955) “the
dipterous larvae were the only scavengers of any consequence in the decomposition of
the carcasses. These provide the basis on which the rest of the fauna, mainly predaceous
beetles and parasitic Hymenoptera depend.”
Bornemissza (1957) studied the effect of carrion decomposition on the soil fauna.
This study showed that soil fauna played only a minor role in decomposition of the
carcasses. Ants and earwigs were the only members of the soil fauna which fed on
carrion. One of the important studies on insects and their relationship to decay rates was
undertaken by Reed (1958) on 45 dog carcasses which revealed much information on the
ecological process and stages of decomposition. It was reported that the total arthropod
populations were greater in summer; however, certain species reached their maximum
population during the cooler periods of the year. Burger (1965) studied the succession of
sarcophagous Diptera in different seasons of the year on mammalian carcasses.
According to Payne (1965) a definite ecological succession occurred among the fauna of
carrion. Each stage of decay was characterized by a particular group of arthropods, each
of which occupied a particular niche. Payne et al. (1968) studied arthropod succession
and decomposition of buried pig carcass. Easton and Smith (1970) pointed out that the
appearance and abundance of fauna are related more to the season than to the stage of
decay. Payne and Mason (1971) reported eighty two species of Hymenoptera associated
with pig carrion. Payne and King (1972), while studying the decomposition of pig
carcasses in water, observed that water limited the number and kind of arthropod
scavengers reaching the animal carcasses. Wasti (1972) carried out study on common
fowl carrion in relation to the incidence and possible succession of arthropods and
remarked that in carrion free from arthropods, the rate of decay was very slow and no
distinct decompositional stages were recognizable.
Lane (1975) studied the blow fly succession on white mice, so as to calculate
precisely and accurately the time of death within a period of 4 to 5 days after death
during which blow flies were the most significant insects present. Denno and Cothran
(1976) studied the competitive interactions and ecological strategies of Sarcophagid and
Calliphorid flies inhabiting rabbit carrion. Nuorteva (1977) established that blow flies are
attracted to carrion in the fresh stage of decomposition but are not attracted to a carcass
when it has progressed to the advanced decay or dry stage. Coe (1978) observed that in
the absence of vertebrate scavengers dipterous larvae consume up to 5% of the soft tissue
of elephant carcasses, the remaining being utilized by microorganisms. McKinnerney
(1978) studied carrion community composition in rabbit carcasses. He described four
decompositional stages and collected eighty arthropod species, out of which sixty three
were identified as participants in the carrion community. According to Putman (1978) out
of all the insects visiting a dead body, the larvae of blow flies and flesh flies are
responsible for the maximum consumption of terrestrial carrion. Johnson and Ringler
(1979) studied occurrence of blow fly larvae in aquatic habitats i. e. on salmon carcasses
and their utilization as food by juvenile fishes. O’Flynn and Moorhouse (1979) studied
blow fly succession on carrion in order to observe the primary flies of summer and winter
seasons and their importance in forensic entomology.
Jiron and Cartin (1981) studied decomposition of dog carcasses in Costa Rica and
divided it into four stages of decay. Braack (1981) enumerated the visitation pattern of
insect species on carcasses in Kruger National Park. The work by Abell et al. (1982) is
one of the very few studies made on fauna of reptilian carrion. O’Flynn (1983) observed
rate of development and succession of blow flies in carrion in Southern Queensland. Lord
and Burger (1984) studied the arthropods associated with Herring Gull and Great black
backed Gull. According to them, carcasses located in vegetated habitats and hence having
less extreme environmental conditions, support significantly higher number of predatory
insects, particularly ants, and fewer carrion consumers, thereby slowing carrion
consumption and decomposition rate. Smeeton et al. (1984) worked on exposed human
corpses. They tried to determine whether certain species were consistently associated
with specific time elapsed after death. Lee et al. (1984) reviewed the use of fly larvae
from human corpses for estimation of PMI. Goddard and Lago (1985) studied blow fly
succession on carrion in order to observe the primary flies of summer and winter seasons
and their importance in forensic entomology. Early and Goff (1986) recorded differences
of up to 22˚C between carcass temperature and ambient air temperature in Hawaiian
Islands. They studied arthropod succession patterns in two different habitats i.e. one in
xerophytic habitat away from human dwelling and other in wetter habitat (mesophytic)
near human dwelling. Smith (1986) described the faunal succession on dead bodies that
included exposed, buried, mummified, and burnt bodies. He also discussed how the
environmental conditions as temperature, humidity and light influence the fauna on the
body.
Von Zuben et al. (1987) studied arthropod succession in exposed carrion in a
tropical rainforest on Oahu Island.According to Nation and Williams (1989) scavengers
can also eliminate insect colonizers on a carcass. Haskell et al. (1989) described the use
of aquatic insects to determine submersion interval. Kashyap and Pillay (1989a, 1989b)
discussed the role of insects in solving crime. They examined and analyzed sixteen insect
infested cadavers to evaluate the reliability of entomological method in estimation of time
elapsed since death, in relation to other medico legal approaches. Blackith and Blackith
(1990) observed that there were about twenty nine species of insects (excluding
Coleoptera) which infest small corpses. Hewadikaram and Goff (1991) compared the
effect of carcass size on rate of decomposition and arthropod succession pattern.
Schoenly (1992) and Schoenly et al. (1992) conducted a statistical analysis of
successional patterns in carrion arthropod assemblages having implications for forensic
entomology and its help in determination of the postmortem interval. Isiche et al. (1992)
found a difference in the calliphorid species abundance and diversity when observing
mouse carrion in sunny and shaded habitats. Four species were found in the sunny area
and only two of these species were observed in the shaded area. According to Lee and
Marzuki (1993) there are differences in community composition and assumptions could
lead to erroneous conclusions pertaining to estimations of time of death. Shean et al.
(1993) compared the decomposition rates of two pig carcasses, kept in close proximity to
each other, one exposed to sun and the other under shade. El-Kady et al. (1994a) carried
out field studies on blow fly and flesh fly succession on exposed rabbit carcasses killed
by different causes. They noted that decomposition of carcasses varied according to the
manner of killing. They also concluded that the manner of death had induced several
noticeable differences in the succession pattern of calliphorids and sarcophagids and in
the rate of development of their immature stages. El-Kady et al. (1994b) studied the
trophic interactions of carrion-attendant arthropods in a botanical garden in Alexandria,
Egypt. Wells and Greenberg (1994a) used goat, rabbit and rat carrion as resource to
identify conditions under which native taxa might avoid interaction with the invaders.
Dillon and Anderson (1995) present a technical report showing that insects colonize
remains in predictable sequence and can be used to assist in determining time of death.
Data generated during this work have been used in investigation of six cases. According
to Wells and Greenberg (1994b) fire ants, Solenopsis geminata (Fabricius), can have a
major impact on necrophagous insects. They found that the colonization of carrion, and
in turn the rate of decomposition, was retarded when fire ants were in significant
numbers. VanLaerhoven and Anderson (1999) present a report showing that predictable
sequence of insect succession occurring on buried carcasses is different from succession
on above ground carcasses. Anderson and VanLaerhoven (1996) conducted a practical
exercise in forensic entomology as how a study of insect activity on corpses and other
crime scene materials can yield valuable evidence. Dillon and Anderson (1996) prepared
a database for insect succession on carrion in northern and interior British Columbia
while Tantawi et al. (1996) studied arthropod succession on exposed rabbit carcasses in
Egypt. Schoenly et al. (1996) conducted a simulation study to quantify statistical
uncertainty in succession-based entomological estimates of the postmortem interval in
death scene investigations. Keiper et al. (1997) presented a report on midge larvae as an
indicator of postmortem submersion interval of carcass. McDonell and Anderson (1997)
described the use of aquatic invertebrates to determine the time since submergence.
Richards and Goff (1997) studied arthropod succession on exposed carrion in three
contrasting tropical habitats on Hawaii Island. Komar and Beattie (1998) studied the
decay of clothed pig carcasses of approximate human size and reported that clothing
disturbance patterns produced by postmortem insect activity mirrored those associated
with a premortem sexual assault. Tomberlin and Adler (1998) made a comparative study
on seasonal colonization and decomposition pattern of rat carrion in water and on land in
an open field.
Bourel et al. (1999) found a considerable difference in blow fly colonization of
rabbit carrion from one year to the next in the same location and during the same sample
period. De Jong and Chadwick (1999) reported a total of fifty three arthropod species
collected from rabbit carrion at different elevations in Colorado. VanLaerhoven and
Anderson (1999) observed differences between succession on buried carrion in two
biogeoclimatic zones which were chosen on the basis of different soil type and
vegetation. Insects are attracted to an animal immediately after death and detection of the
remains can be influenced by their presence (Smith, 1986; Bourel et al., 1999; Anderson,
1999, 2000). Carvalho et al. (2000) gave a checklist of arthropods associated with pig
carrion and human corpses in Southeastern Brazil. Davis and Goff (2000) compared the
decomposition pattern in terrestrial and inter tidal habitats in Hawaii islands. Ma (2000)
studied constitution and succession of insect community on pig carcass in Hangzhou
while Singh and Bharti (2000) provided a list of forensically important blow flies of
Punjab (India). Shalaby et al. (2000) compared patterns of decomposition in a hanging
carcass and carcass in contact with soil in a xerophytic habitat on the island of Oahu,
Hawaii. LaMotte and Wells (2000) gave p-Values for Postmortem intervals from
Arthropod Succession Data. P-value obtained is based on likelihood ratio statistic and
Fisher’s exact test which show comparison of arthropod species present on a mystery
carcass to the observed frequency distribution of carcasses exposed to the elements.
According to Anderson (2001b) a corpse progresses through a recognized
sequence of decompositional stages, from fresh to skeletal, over time. Each of these
stages of decomposition is attractive to a different group of sarcosaprophagous
arthropods, primarily insects. Singh and Bharti (2001a) enlisted eight species of ants
collected from rabbit carcasses during successional studies in the state of Punjab, India.
Keiper and Casamatta (2001) and Merrit and Wallace (2001) described importance of
benthic organisms as forensic indicators. Joy et al. (2002) compared the larval activity on
sunlit and shaded raccoon carrion for a 153h period during the spring. They determined
that the maggot mass temperatures in sun and shade-exposed carrion were the same;
however, the mean developmental times for P. regina larvae collected from sun-exposed
carrion were greater than those shaded carrion. Anderson et al. (2002) determined time of
submergence using aquatic invertebrate succession and decompositional changes.
Kirkpatrick and Olson (2002) compared the summer succession of necrophagous and
other arthropod fauna associated with fresh and frozen pig carcasses. Oliva (2001) and
McDowell (2002) described the importance of Diptera in forensic science. Watson and
Carlton (2003) reported ninety three arthropod species associated with black bear, deer,
alligator, and pig carrion in Louisiana.
Bharti and Singh (2003) studied the succession of insect communities on rabbit
carrion in the state of Punjab, India. They reported thirty eight species of insects
belonging to thirteen families from different stages of carrion decay during various
seasons of the year. Grassberger and Frank (2004) studied arthropod succession on pig
carrion in central European urban habitat while Grassberger et al. (2003) described
Chrysomya albiceps as a new forensic indicator in Central Europe. Iannacone (2003)
studied the forensically important arthropod fauna on pig carcass in Peru while Anderson
and Hobischak (2004) observed decomposition of marine carrion. Haefner et al. (2004)
observed pig decomposition in lotic aquatic system and used algal growth as indicator of
PMI. Bourel et al. (2004) studied the entomofauna of buried bodies in France. Carvalho
et al. (2004) exposed carcasses of domestic pig in an urban area to determine stages of
decomposition and insects of forensic significance exploiting the carcasses. Leccese
(2004) sampled several species of forensically important insects using pig meat as bait.
Gruner (2004) gave a list of forensically important Calliphorids collected from pig
carrion in rural North-Central Florida. Slone et al. (2004) described investigations into
the thermal behavior of forensically important larvae, the effect of internal maggot mass
heat generation on maggot development time, and the sources and magnitudes of error
affecting a phenological computer model that predicted the likely postmortem interval
(PMI) of human remains found long after the person’s demise.
Gill (2005) provided a technical report on decomposition and arthropod
succession pattern on pig carrion in rural Manitoba. Morette and Ribeiro (2006) reported
the occurrence of Tachinaephagus zealandicus parasitizing pupae of Chrysomya
megacephala associated with a decomposing rat carcass in a secondary wood area in
Campinas. Vitta et al. (2007) conducted a preliminary study on insects associated with
pig carcasses. Five decomposition stages of pig carcasses were categorized: fresh (0-1
day after death), bloated (2 days after death), active decay (3 days after death), advanced
decay (4-6 days after death) and dry (7-30 days after death). The arthropod species
collected from corpses in the field sites were classified as mainly belonging to two orders
and nine families. Heo et al. (2008) studied insect succession on a decomposing piglet
carcass placed in a manmade freshwater pond in Malaysia. Wang et al. (2008) studied
decomposition of pig carcasses placed in the outdoor environment in different seasons to
observe and select the critical entomological index in accurate estimation of PMI.
According to Beningern et al. (2008) cadaver decomposition did not result in a
significant difference in soil carbon and moisture content. However, significant increases
were observed in the concentration of soil pH, total nitrogen, soil-extractable phosphorus,
and lipid-phosphorus. According to them there is a significant increase in the
concentration of grave soil nutrients that represented a maximum after PMI of 43 days
(lipid ), 72 days (total nitrogen), or 100 days (soil-extractable phosphorus). Soil-based
method has the potential to act as a tool for the estimation of extended PMI.
Matuszewski et al. (2008) studied insect succession and carrion decomposition in
various forest habitats of Central Europe. There were no differences between forests in
the sequence of insect occurrence on carrion. However, differences between forests in
occurrence time and activity period of some taxa were found. Heo et al. (2008) studied
insect succession and rate of decomposition on a partially burned pig carcass in an oil
palm plantation in Malaysia. They compared the stages of decomposition and faunal
succession between a partially burnt pig (Sus scrofa) and natural pig (as control). The
burning simulated a real crime whereby the victim was burnt by murderer. Results
showed that there was no significant difference between the rate of decomposition and
sequence of faunal succession on both pig carcasses. The only difference noted was in the
number of adult flies, whereby more flies were seen in the control carcass. Anderson
(2008) conducted a study that followed decomposition and animal scavenging on a
carcass which helped to explain artifacts and decomposition of a body submerged in
deep water. Michaud and Moreau (2009) demonstrated that the occurrence probability of
some carrion-related insects on carcasses can be estimated from meteorological records
even across seasons with different rates of degree-day accumulation.
Gomes et al. (2009) studied insect succession on carcasses decomposing in a
sugarcane crop in Brazil. In all seasons, C. albiceps and C. macellaria were frequent
visitors during the fresh and bloated stages of decomposition, whereas Dermestes
maculatus, Necrobia rufipes and Oxelytrum sp. were characteristic at the most advanced
decomposition stages. The fact that climatic variations influence the occurrence of insect
species and vegetation in the tropics may help to solve crimes through sampling of the
local insect fauna, as may the fact that only certain groups of insects occur in specific
regions. Segura et al. (2009) studied succession pattern of cadaverous entomofauna in a
semi-rural area of Bogotá, Colombia. They examined the succession of insects colonizing
three pig (Sus scrofa) cadavers. In total 5981 arthropods were collected during
decomposition, 3382 adults and 2599 immature stages, belonging to 10 orders and 27
families. Voss et al. (2009) study annual, seasonal and shorter term variation in patterns
of insect succession on decomposing remains at two contrasting locations in Western
Australia. Insect assemblages were strongly correlated between locations, within
corresponding time periods, indicating that patterns of insect succession were similar
between localised sites within the same broad geographic area. Matuszewski et al. (2009)
monitored insect fauna of pig carcasses in different seasons and forests of Western
Poland. The composition of carrion fauna and selected features of residency in carrion in
adults and larvae of particular taxa were analysed. A total of 131 adult and 36 larval
necrophilous taxa were collected. Only 51 adult species and 24 larval taxa were
minimally abundant (≥10 specimens) at least on one carcass. Reibe and Madea (2010)
investigated the time taken by blow flies to find and oviposit on fresh carcasses placed
outdoors and indoors. Paired dead piglets, one in the open and the other in a nearby room
were exposed simultaneously on nine occasions. In all cases the indoor piglet carcass was
exclusively infested by Calliphora vicina; only in one case, on a very hot day after a 48h
exposure did Lucilia sericata infest an indoor carcass. The outdoor piglets were infested
by a variety of common corpse-visiting species: L. sericata, L. caesar, L. illustris, C.
vicina and C. vomitoria. Oliveria and Vasconcelos (2010) analyzed the occurrence of
forensically important insect species (Order Diptera) on fourteen cadavers taken into the
Institute of Legal Medicine (ILM), in Pernambuco, Brazil, according to the conditions of
the body and the pattern of colonization by insects. Five species were present on cadavers
: C. albiceps, C. megacephala and C. macellaria (Calliphoridae), Oxysarcodexia
riograndensis and Ravinia belforti (Sarcophagidae).
There are so many factors affecting insects succession which include geographic
distribution, season, temperature, humidity, habitat, and biology of carrion insects as has
been demonstrated in large number of studies (Hanski, 1987; Levot et al. 1979; Hutton
and Wasti 1980; Cianci and Sheldon, 1990; Greenberg, 1990; Goff, 1993; Hall and
Doisy, 1993; Byrne et al., 1995; Grisbaum et al., 1995; Byrd and Butler, 1996; Johl and
Anderson, 1996; Dillon, 1997; Avila and Goff, 1998; DeCarvalho and Linhares, 2001;
Arnalds et al., 2001; Anderson and Hobischak, 2002a, 2002b; Archer, 2003; Archer and
Elgar, 2003; Archer, 2004 and Tabor et al., 2004).
The other method to estimate PMI utilizes the stage of development of the oldest
larvae feeding on the corpse, from which one can determine a close approximation of the
minimum time since death. Insects often lay eggs within minutes or hs after death (Catts
and Goff, 1992) thus providing a developmental reference. According to DeJong (1995)
the blow flies can find a dead body within few seconds of exposure. Because most bodies
are discovered with in the first few days or weeks, blow flies are encountered more
frequently, and can reveal time of death more accurately than their successors
(Greenberg, 1991).
For estimating the minimum PMI, the age of the available larval stages must be
determined. Various procedures for estimating their age exist, but all are based on the fact
that the rate of development depends on the ambient temperature. The approach, known
as thermal summation (Wigglesworth, 1972), is the accumulation of degree hours (ADH)
or degree days (ADD). However, when using estimates of ambient temperature to
calculate development rates, it should be noted that these data are not necessarily
representative of the temperatures experienced by the insects in the corpse. Large
numbers of larvae may create a so-called “maggot mass effect” which, according to the
metabolic and feeding rate of these immature insects, can generate a temperature
substantially higher than ambient (Wells and LaMotte, 1995).
Life history and morphology of immature stages of blow flies
In forensic entomology, information is essential not only about the developmental
stages of the insects found on the body, but also on their identity. Morphological methods
are usually helpful for this purpose (Schumann, 1971; Smith, 1986; Povolny and Verves,
1997). Wijesundara (1957) studied the life history and bionomics of C. megacephala in
Ceylon. Kamal (1958) investigated the effect of controlled temperature and humidity on
the life history, rate of development and other biological activity of both adults and
immature stages of thirteen species of flies, representing nine genera within the families
Sarcophagidae and Calliphoridae. Kitching (1976) described and illustrated the eggs,
three larval instars and puparia of C. bezziana. He also compared them with five other
species of Chrysomya found in Africa and Oriental region. The most common stage
found on the corpse is generally the larva and its identification is a must from forensic
point of view. Subramanian and Mohan (1980) studied the life history, bionomics and
reproduction strategy of blow flies C. megacephala, C. rufifacies and L. cuprina. Teskey
(1981) described in detail the morphology and terminology of Dipteran larvae including
those of sarcophagous families. Prins (1982) gave morphological and biological notes on
six South African blow flies and their immature stages. Greenberg and Szyska (1984)
reared fifteen species of Peruvian blow flies to study the structure of their egg plastrons,
larval instars and puparia. They also gave a key to the larvae of known species of Peru
apart from studying their developmental rates and diet activity. Erzinclioglu (1985b)
provided descriptions based on a detailed comparative study of the structural features
of all three larval instars and pupae of the six British Calliphora
and single
Chrysomya species. Results demonstrated that certain characters, singly or in
combination, enable reliable species separation and keys were provided to third instar
larvae and pupae of all these species. Erzinclioglu (1987) described diagnostic
features of 3rd instar larvae of ten species of blow flies of medical and veterinary
importance. He also described characters for recognition of the early instar larvae of
genera Calliphora and Lucilia. Erzinclioglu (1988) further described three larval stages
of the blow flies, Phormia terranovae, Phormia regina and Borellus atriceps and
discussed biology of these flies which according to him were adapted to a cold climate.
Liu and Greenberg (1989) provided identification keys and diagnostic
descriptions for eggs, three larval stages and puparia, of seventeen species of forensically
important flies. Erzinclioglu (1990) studied the larvae of two closely related blow fly
species of the genus Chrysomya. Peterson and Newman (1991) studied in detail the
chorionic structure of egg of screwworm fly C. hominivorax. Greenberg and Singh
(1995) studied eggs of eleven forensically important calliphorid species belonging to six
genera with the help of scanning electron microscope for useful diagnostic characters.
Amorion and Riberio (2001) studied morphological differences among the puparia of
three blow flies species. Results of the study are useful in species identification and from
forensic point of view. According to Wallman (2001) the detection of carrion-breeding
blow flies provides valuable forensic indicators of time, place and manner of death. Their
correct identification is crucial to their successful use in this way. A particular challenge
to blow fly identification lies in the morphology or structure of blow fly larvae.
Bharti and Singh (2002) reported the occurrence of larval stages of blow flies during
different stages of decay in rabbit carcasses. Sukontason et al. (2003a) studied the surface
ultra structure of C. rufifacies larvae. Morphological changes were greatest from the first
to the second instar, but less from the second to the third instar. Sukontason et al. (2003b)
further studied larval morphology of C. megacephala using scanning electron microscope
which can help to differentiate C. megacephala from other larvae found in decomposing
human corpses.
Sukontason et al. (2004b) identified eggs of forensically important fly species using
potassium permanganate staining techniques while Sukontason et al. (2004a)
differentiated third instars of six forensically important fly species in Thailand with the
features of the anterior spiracles, dorsal spines between the prothorax and mesothorax,
and posterior spiracles. Chigusa et al. (2006) also identified the species and instar of
several species of blow flies. C. megacephala egg ultramorphology was analyzed by
David (2008) to generate data for further comparison with other species. Sukontason et
al. (2008) studied larval morphology and developmental rate of C. megacephala and C.
rufifacies, the two forensically important blow fly species in Thailand.
Effect of starvation on larval behavior
According to Ullyett (1950) each larva attempts to feed as much as possible to attain
optimum size before the food supply is exhausted. Subramanian and Mohan (1980)
reported that C. rufifacies attain postfeeding stage after 60-70h of hatching. William and
Richardson (1983) studied effect of artificially reduced amount of larval food on life
history of L. cuprina, C. stygia, C. vicina and C. hilli. With increasing food shortage, the
puparia were reduced upto 12% of weight attained under conditions in which food
was unlimited. There is no effect on egg size but reduction in the number of ovarioles.
Larval stage is the main period when blow flies face limited food resources. Since these
substrates are often booming in insects of various kinds, there is often an intense
competition for resources (Hanski, 1987). Goodbord and Goff (1990) studied that with
declining food, the immature larvae leave the carrion and search for alternative food
resource. During this period if they are unable to get any food source then they enters the
period of forced starvation. According to Ives (1991) the substrates (read decaying
carrion) in which blow fly larvae develop are discrete and ephemeral. Reis (1994) stated
that competition for food is usually of an exploitative type. According to Wells and
Kurahashi (1994) C. megacephala attain postfeeding stage after 68 h of hatching at 27◦C.
According to Campobasso et al. (2001) the fully grown mature larvae search for
a place to pupate and disperse away from the carrion. However, if they are not heavy
enough to pupate, the larvae may move to another source of food in the vicinity.
According to Shiao and Yeh (2008) third instar larvae of C. rufifacies will expel C.
megacephala larvae from their foods by using their fleshy protrusion on body surface,
and the C. megacephala will be forced to pupate earlier by decreasing their larval growth.
Under mixed-species rearing of different ratio, the larval duration of C. rufifacies will
increase as the ratio increases, but this result was not exhibited in C. megacephala.
According to Ireland and Turner (2006) use of entomological evidence in the estimation
of the minimum PMI generally depends on the size and developmental stage of blow fly
larvae collected from a corpse. So, the factors which can have an effect on the larval size
and growth rate can have implications for reliable minimum PMI determinations.
Dispersal behavior of postfeeding larvae
First study to consider the burrowing depth reached by fly larvae was done by
Travis et al. (1940) who studied lateral migration and depth of pupariation by the larvae
of the primary screwworm Cochliomyia americana. Green (1951) studied the behavior of
blow fly larvae in the field and observed that they could travel distances of 6–10m from
the center of dispersal. Lundt (1964) found that blow flies could be completely excluded
by burial under only 2.5cm of soil. Nuorteva (1977) showed that under natural
conditions, pupae of several dipteran species can be found directly under an animal
corpse or as far away as 6m. Coe (1978) found that for the larvae of two species of
Chrysomya feeding on elephant carcasses in Kenya, larvae of C. albiceps preyed on the
smaller C. marginalis only in the migratory phase as they left the carcass. Smith (1986)
investigated the factors controlling the timing of the exodus of L. cuprina larvae from
sheep and carrion at night under field and controlled conditions. This type of analysis is
important because it can improve the precision with which the minimum PMI is
estimated.
Vogt and Woodburn (1982) studied the dispersal of postfeeding larvae of L.
cuprina from carrion and found that most of the larvae entered the soil in the immediate
vicinity of the host. In addition, most of the larvae sampled were located in the top 2.5 cm
of soil with none penetrating beyond a depth of 5cm. The type of host also appeared to
influence the subsequent dispersal of the postfeeding larvae. Smith (1986) discussed
several important aspects of postfeeding larval behavior associated with the methods and
techniques applied in forensic entomology. Empty puparia would indicate
that a generation of flies had emerged, although such puparia still contained the third
instar mouthparts and spiracles that could be used to identify the fly species. Hanski
(1987) described an outdoor cage experiment to prove that localized interactions
facilitated the coexistence of species breeding in ephemeral habitats which can affect
subsequent search for a suitable pupariation site by the dispersing postfeeding larvae.
Greenberg (1990a) compared the dispersal behavior of postfeeding larvae of
forensically important fly species in an 8m long channel. The results suggested that
postfeeding larvae of Calliphorinae moved farther from the food source, pupated
underground, and produced a thinner puparium followed by a longer pupariation period
when compared to the larvae belonging to Chrysomyinae. Omar et al. (1994) studied
certain behavioral patterns of Malaysian Calliphorid and Muscid species on decomposing
cat and monkey carcasses and noted that the late third instar larvae of C. rufifacies,
Chrysomya chani, C. villeneuvi, and Ophyra spinigera were the least dispersive
compared to Chrysomya megacephala, Chrysomya nigripes, Chrysomya pinguis and
Hemipyrellia ligurriens. In addition, predatory behaviour by third instar larvae of C.
rufifacies, C. villeneuvi and O. spinigera and cannibalism by C. rufifacies and C.
villeneuvi were observed in the field.
Godoy et al. (1995, 1996) observed an oscillation in the pupal frequency of C.
megacephala and C. putoria as a function of the distance from the feeding substrate.
According to Boldrini et al. (1997), these oscillations could be the result of larval
aggregations at certain sites in the substrate used for pupariation. Von Zuben et al. (1996)
proposed a diffusion model to describe dispersal of larvae that were already buried
in the substrate. Bassanezi et al. (1997) fitted the model to the data for the postfeeding
larval dispersal of calliphorids obtained by Godoy et al. (1995). Tessmer and Meek
(1996) investigated the spatial distributions of Calliphorid pupae based on adult
emergence from pig carcasses under field conditions during diffrent seasons. Boldrini et
al. (1997) developed a mathematical model to explain the appearance of oscillations
during the dispersal of larvae from the food source. Bass (1997) studied the exodus of
larvae from pig carcasses on a farm and put forward the view that the larvae left the body
to avoid predators and pushed themselves through the soil up to 25 feet away. Kocárek
(2001) investigated the postfeeding dispersal of larvae of C. vomitoria and L. caesar
from carrion in the field and found that the larvae dispersed exclusively at night, thereby
minimizing interactions with diurnal and crepuscular predators. Andrade et al. (2002)
used an acrylic channel to examine the influence of predation on larval dispersal in C.
albiceps and C. macellaria.
Other studies have described general aspects of larval dispersal in a circular arena
and have confirmed results obtained using troughs (Gomes et al., 2002, 2003). Unlike the
dispersal in only two directions allowed by a trough, a circular arena allows radial
dispersal from a central feeding substrate. They concluded that the larvae with the
smallest mass tended to move greater distances after food depletion, perhaps in search of
new sources of food rather than for a site to pupate. In the wild, postfeeding larval
dispersal and the subsequent spatial distribution of pupae at pupariation sites could have
implications for the susceptibility of larvae to attack by predators or parasites (Pescke et
al., 1987). Because C. albiceps larvae prey on C. megacephala larvae, the latter probably
disperse farther and deeper to escape predation (Hanski, 1987; Goodbrod and Goff, 1990;
Wells and Greenberg, 1992; Faria et al., 1999; Faria and Godoy, 2001). As shown by
Gomes et al. (2003), when both species were considered together, there was a positive
correlation between the distances from the food source and the depth of burrowing, which
indicated a significant correlation with sample size of larvae dispersing in this study. C.
albiceps larvae concentrated closer to the center of the arena and did not have a uniform
distribution, whereas C. megacephala larvae had a uniform distribution. This
arrangement probably reflected the tendency of the latter species to minimize contact
with C. albiceps larvae to avoid predation (Faria and Godoy, 2001).
In additional experiments vermiculite and sawdust were used to assess the influence of
substrate compactness and density on larval dispersal (Cardoso et al., 1992). Most of the
larvae burrowed to a depth of 7–12 cm before pupating, in contrast to the study by
Gomes et al. (2003) in which most larvae burrowed to a depth of 10–15 cm before
pupariation. Hence, the type of substrate clearly affected the depth of burrowing but not
the pattern of postfeeding larval dispersal. Gomes and Von Zuben (2005) studied some of
the most important aspects of larval dispersal in the blow fly C. albiceps by using a
circular arena to allow the radial dispersion of larvae from the center. Most of the larvae
buried themselves near the center of the arena. Gomes et al. (2006a) reviewed
postfeeding larval dispersal in blow flies. Gomes et al. (2006b) studied influence of
photoperiod on body weight and depth of burrowing by larvae of C. megacephala. Roux
et al. (2006) studied circular dispersal of larvae of P. terraenovae and found the shape of
the dispersal to be circular with a concentric distribution around the feeding zone. Gomes
et al. (2007) studied combined radial postfeeding behavior of C. albiceps and C.
megacephala. According to Arnott and Turner (2008) postfeeding dispersal in blow fly
larvae under laboratory conditions is typically very short but may extend for hs or days in
the field, because larvae try to find a suitable pupariation site. Lima et al., (2009)
performed a computational analysis employing a cellular automata model to investigate
the larval dispersal behavior of blow flies. The spatially discrete model developed here,
incorporates simple behavioral rules in local interactions to produce the large-scale
patterns observed in the larval dispersal process. In particular, oscillations, initially
explained as a response to larval aggregation, could be explained by the combination of
different mechanisms acting during the dispersal process.
An analysis of environmental factors, particularly photoperiod, can be helpful
when searching for dispersing larvae around cadavers (Amendt et al., 2004a). The study
of blow fly larval dispersal can be of crucial importance in minimum PMI determination
because the interval will be underestimated if older dispersing larvae or those that
disperse farther, faster, and deeper are not considered (Smith, 1986; Von Zuben et al.,
1996; Gomes et al., 2002, 2003; Gomes and Von Zuben, 2004, 2005).
Development at different temperatures and correlation between larval age, body
length and dry weight
Evans (1934) put forward the view that increase in temperature may lead to an
increase in the speed of development and, therefore, may have a detrimental effect on the
accuracy of PMI calculations. Deonier (1940) studied the relationship of carcass
temperature to winter blow fly population and activity and pointed out that after
establishment of larvae on carcass, its temperature rises than that of the ambience.
Davidson (1944) studied effects of temperature on developmental time of blow fly life
cycles and define relationship between temperature and rate of development of insects at
constant temperatures. Kamal (1958) investigated effect of controlled temperature and
humidity on the life history, rate of development and other biological activity of both
adults and immature stages of thirteen species of flies belonging to the families
Sarcophagidae and Calliphoridae. He also studied the nutritional aspects of larval forms
with special emphasis on how the quantity and quality of food affect life span, rate of
growth and size of both individuals and populations with regard to maggot development
rate. Payne (1965) reported that carcass temperatures often get elevated due to heat
generated by maggot masses and that ambient temperature might not reflect the one to
which larvae are exposed. According to Levot et al. (1979) the relative success of each
carrion fly species depended upon the ability of the larvae to attain quickly the minimum
weight for viable pupariation. Calliphora nociva, Calliphora augur, Chrysomya
megacephala and Chrysomya rufifacies were the species best adapted to pupariation at
low larval weight i.e., their food requirement for successful pupariation were less than
those of other species. Dallwitz (1984) studied influence of constant and fluctuating
temperatures on developmental rate and survival of pupae of L. cuprina. Nishida (1984)
developed growth tables and growth curves for seven species of blow flies and flesh flies
at 15°C, 20°C, 25°C, 30°C and 35°C. On the basis of this study time of molting,
pupariation or emergence of adults for each species at different temperatures could be
calculated. The stabilizing effect of maggot mass generated heat was studied in human
remains by Vinogradova and Marchenko (1984) who also presented threshold
developmental temperatures for nine species of blow flies.
Williams (1984) developed a computer model for determining the time of blow fly egg
hatching based on maggot weight and temperature record. Williams and Richardson
(1984) observed that higher temperature of mixed species maggot mass was tolerated by
C. rufifacies but the population of L. cuprina was burned out. Introna et al. (1989)
studied life cycles of L. sericata reared in the field with continuous registration of
temperature, humidity and luminosity. When compared to parallel life cycles after rearing
the flies in a growth cabinet, the results showed no statistical difference between the field
and laboratory conditions. Goodbrod and Goff (1990) studied effect of population density
on rate of development of two species of blow flies. Rearing of C. megacephala and C.
rufifacies in pure cultures at seven different population densities (larvae per gram of
liver) demonstrated an inverse relationship between density and the duration of the larval
stage. According to Block et al. (1990) of all the stages in the life history of blow flies,
pupae have the smallest percentage of water compared to body weight. Hagstrum and
Milikan (1991) studied differences in insect developmental times between constant and
fluctuating temperatures. Catts (1992) discussed the influence of maggot generated heat
on corpse community development and on subsequent analysis of entomological data.
The level of heat generated in a maggot mass could also selectively affect larvae of
different species as recorded by Turner and Howard (1992). Tantawi and Greenberg
(1993) and Adams and Hall (2003) checked the effect of killing and preservative
solutions and estimates of maggot age in forensic cases. They found that there was
shrinkage in various solutions used as preservatives and concluded that larvae killed in
boiling water and then placed in preservative solution did not shrink and recommended
such treatment of larvae if their length was to be interpreted forensically in a valid and
consistent way. Singh and Greenberg (1994) studied survival after submergence in the
pupae of five species of blow flies and found that the maximum period of submergence
for the pupae after which they could develop into normal adults was four days. These
data are potentially useful in estimating duration of submergence of corpse during
forensic investigations where the corpse got submerged after pupariation. Wells and
Kurahashi (1994) studied the development of C. megacephala at 27˚C and observed that
there were differences in the length of postfeeding larvae and attributed these differences
to their sensitiveness to environmental conditions. Wells and LaMotte (1995) estimated
maggot’s age from its weight using inverse prediction and also constructed a confidence
interval on age of larva, given its weight.
Johl and Anderson (1996) studied the effect of refrigeration of immature stages on
the development of Calliphora vicina at a temperature of 3˚C for 24h and concluded that
such a treatment of any stage (egg, larva, and pupa) induced a 24h delay in adult
emergence. Milward-de-Azevedo et al. (1996) checked the influence of temperature on
the postembryonic development of Chrysomya megacephala in incubators regulated at
18˚C, 24˚C, 30˚C and 35˚C. Similarly Byrd and Butler (1997) observed effects of
temperature on C. rufifacies development. Growth curves were studied for the egg, larva
and pupa under mean cyclic temperatures of 15.6˚C, 21.1˚C, 26.7˚C, and 35.0˚C and a
constant temperature of 25.0˚C. Allen and Byrd (1999) developed computer modeling of
insect growth for the purpose of improving accuracy in estimating time of death in the
field of forensic entomology. Nelson (1999) estimated minimum postmortem interval
(PMI) through observation and measurement of body conditions such as core body
temperature.
Anderson (2000) laid stress on the concept of accumulated degree days (ADD)
and accumulated degree hours (ADH). To calculate the ADD or ADH, the length of time
taken for each developmental stage is multiplied by the temperature at which the insect
was reared. According to Dadour et al. (2001) it is important to know how long it takes
for the insect to arrive on a corpse, the stage of decay to which it is attracted, its life cycle
and its rate of development. Byrd and Allen (2001) studied the development of black
blow fly Phormia regina which is an important fly from forensic point of view. Centano
et al. (2002) demonstrated that sheltering is another vital factor that must be considered
in PMI calculations due to the variations in decomposition shown over the various
seasons. Grassberger and Reiter (2001, 2002) studied effect of temperature on the
development of two forensically important blow flies while Vanlaerhoven and Anderson
(2001) used the development rates of blow flies eggs to determine postmortem interval.
Wang et al. (2001)
studied
chronology of development
within
puparium of C.
megecephala at different constant temperatures which could help in estimation of
postmortem interval. Wang et al. (2002) further observed the effect of temperature on the
body length change of C. megacephala that has implications to forensic entomology.
Silva et al. (2004) analyzed the theoretical population dynamics of C. megacephala kept
at
constant
temperatures using
a density-dependent
mathematical model, with
parametric estimates of survival and fecundity in the laboratory. Kaneshrajah and Turner
(2004) studied larval growth rate of Calliphora vicina at different body tissues and
compared it with the rate of development on pig’s liver and found that the larval growth
was significantly faster by as much as 2 days on lung, kidney, heart or brain tissue. Gabre
et al. (2005) also provided a life table of C.
megacephala reared at 26˚C in the
laboratory.
Day (2006) studied the influence of substrate tissue type on larval growth in two
species of blow flies and proposed width as an alternative measurement to length for
postmortem interval estimations. It was found that conclusions drawn on the basis of
body width, as measured at the junction of the fifth and sixth abdominal segments, are
comparable with those of body length for age prediction of larvae. Donovan et al. (2006)
studied the larval growth rate of C. vicina at temperatures of between 4°C and 30°C,
under controlled laboratory conditions. Ireland and Turner (2006) studied the effects of
larval crowding and food type on the size and development of C. vomitoria larvae. The
competitive feeding environment within the more crowded larval cultures resulted in
increased development rates and the production of undersized larvae and adults.
Zhu et al. (2006) suggested that cuticular hydrocarbon composition is a useful
indicator for determining the age of larvae of C. rufifacies, especially for postfeeding
larvae, which are difficult to differentiate by morphology. Huntington et al. (2007)
studied maggot development during morgue storage and its effect on estimating the
postmortem interval. Nabity (2007) studied light induced variability in the development
of P. regina and found that photoperiod altered development and behavior among
calliphorids. Bharti et al. (2007) observed the effect of temperature on the development
of C. megacephala reared in the laboratory at four constant temperatures (22˚C, 25˚C,
28˚C, 30˚C). Charabidze et al. (2008) investigate variation in the crawling speed Kocarex
of Protophormia terraenovae larvae as a function of body length and ambient
temperature. As temperature increased, the larvae crawled at a faster speed. Furthermore,
speed increased as a function of body length.
Aaron and David (2008) presented a method for modeling growth of L. sericata,
using generalized additive models (GAMs). Eighteen GAMs were created to predict the
extent of juvenile fly development, encompassing developmental stage, length, weight,
strain, and temperature data, collected from 2559 individuals. Richards et al. (2008)
constructed developmental curves for C. albiceps at 13 different constant temperatures
using developmental landmarks and length as measures of age. The thermal summation
constants (K) and developmental zeros (D0) were calculated for five developmental
landmarks. Richards and Villet (2008) investigate the effects that different summary
statistics (minimum, median, mean, or maximum) temporal sampling resolutions
(duration between sampling events) and sample sizes (number of individuals sampled per
sampling event) had on the accuracy and precision of the regression coefficients of a
typical thermal summation model used to calculate minimum postmortem interval (PMI).
No significant differences were found in the values of the developmental constants
calculated from different summary statistics of the duration of development of blow flies.
Shiao and Yeh (2008) studied larval competition between two forensically important
blow flies C. megacephala and C. rufifacies. Richards et al. (2009) constructed
developmental curves for the sister species C. chloropyga and C. putoria reared at eight
and 10 different constant temperatures, respectively, using developmental landmarks and
body length as measures of age.
Vanlaerhoven (2008) evaluated the use of different degree day (DD) models,
developmental thresholds and developmental data sources for estimating postmortem
interval (PMI) based on developmental rates of blow flies (Diptera: Calliphoridae). Blow
fly evidence was collected from three mock crime scenes and sent for blind analysis of
PMI. PMI estimates were calculated using averaging, single sine, double sine, single
triangle, and double triangle models of DD calculation with minimum developmental
thresholds of 0, 6 and 10 ◦C. Gomes et al. (2009) studied the influence of temperature on
the behavior of burrowing in the larvae of Chrysomya albiceps and L. cuprina under
controlled conditions Depth of burrowing was affected differently by temperature for
both of the species studied; L. cuprina larvae burrowed deeper at lower and higher
temperatures while C. albiceps larvae burrowed less at extreme temperatures. Gallagher
et al. (2010) investigated the developmental rate variation between populations of L.
sericata. In a series of common garden experiments at 16°C, 26°C, and 36°C. The
distribution of developmental times differed significantly between the three populations
within each temperature treatment. Study demonstrates the importance of assembling
local population-specific developmental tables when estimating larval age to determine
PMI. Niederegger et al. (2010) compared the development of larvae of different
forensically important flies under constant low, medium and high temperatures as well as
under daily fluctuating temperatures in a climatic chamber. Results suggest faster
development under fluctuating temperatures for Sarcophaga argyrostoma and Lucilia
illustris but slower development for Calliphora vicina and Calliphora vomitoria.
Fluctuating temperatures had a higher impact on larvae in feeding stages than in
postfeeding stages.
Several other workers have made observations on the effects of temperature on
the development of various fly species, geographic differences in fly communities and
carrion insect succession on different media (Baumgartner and Greenberg, 1985; Goff et
al., 1989; Introna et al., 1990; Goff et al., 1991a; Goff, 1992; Turner and Howard, 1992;
Gaur, 1993; Byrd and Butler, 1996; Byrd and Butler, 1998; Anderson, 2000; Feng,
2002a; Feng, 2002b). Fertilization in Diptera is often quite complex and it would be
appropriate to base the estimate of minimum PMI on the age of the larval stage that is
present in largest numbers, i.e. the stage representing the progeny resulting from eggs
fertilized during oviposition (Erzinclioglu, 1990). Besides, nocturnal oviposition
/larviposition in several Dipterans can alter the estimate of PMI by as much as 12 h
(Greenberg, 1990b) which has been confirmed by Singh and Bharti (2001b, 2008). It is
also important to consider factors that might alter the time of oviposition, such as
covering corpses with branches or tight wrapping with blankets, carpets or plastic bags,
and indoor placement, because these factors may delay initial oviposition (Higley and
Haskell, 2001). Similarly, seasonal influences, such as cold and rainy weather, may
inhibit or even prevent fly activity and delay oviposition (Erzinclioglu, 1996). Diapause,
the period during which growth and development of insects is suspended, is one more
challenge for the forensic entomologists (Ames and Turner, 2003). Declining day length
and/or decreasing temperatures indicate approaching winter and induce diapause,
preventing development under unfavourable environmental conditions. Competition may
also affect development and growth of the larvae (Smith and Wall, 1997a, 1997b).
Workers like Reiter (1984), Smith (1986) and Erzinclioglu (1990) pointed to another
factor which could complicate the estimation of the postmortem interval—precocious egg
development in flies. In some female flies, eggs may be retained in the oviduct, having
been fertilized as they pass the spermathecal ducts in advance of the act of oviposition
(Wells and King, 2001).There are few reports on the use of parasitoids in forensic
entomology (Smith, 1986; Haskell et al., 1997; Amendt et al., 2000; Anderson and
Cervenka, 2002; Grassberger and Frank, 2003b). The parasitoid larvae feed exclusively
on other arthropods, mainly insects, resulting in the death of their host (Godfray, 1994).
Fabritius and Klunker (1991) listed eighty three parasitoid species, mainly wasps, which
attacked the larval and pupal stages of synanthropic Diptera in Europe. However, when
thinking about the potential influence, especially of larval parasitoids, it is important to
remember that this specialized group might also create significant problems for forensic
entomology. Holdaway and Evans (1930) described, for example, the change in
developmental times for L. sericata after the attack by its parasitoid Alysia manducator,
which resulted in premature pupariation. Forensic experts also come across situations
when the body has been moved from the original scene of the crime. In a landmark case
in Belgium, forensic entomologists observed five species of Staphylinids on the bones
of a corpse but the absence of other insect species in spite of favorable conditions
suggested that the murder was committed elsewhere (Leclerq and Vaillant,1992). In
addition, the biochemical differences among geographical populations may help in
determining corpse relocation and in the study of population ecology of species and
populations. Buchan and Anderson (2001) reviewed the various methods used in later
minimum PMI estimations. A new method has been described by Bourel et al. (2003) for
calculating short term PMI by studying flies eggs. A few researchers have published
diagnostic descriptions of eggs, larval instars and puparia and alternate techniques for
estimating maggot age for forensically important flies (Erzinclioglu, 1989b; Liu and
Greenberg, 1989; Greenberg and Singh, 1995; Wells and Lamotte, 1995; Clarkson et al.,
2005).