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Forensic entomology

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Forensic entomology is the science and study of insects and other arthropods with law-related applications. It can be divided in three subfields: urban, stored-product and medico-legal/medico-criminal.

Urban forensic entomology typically concerns pest infestations in buildings or gardens that may be the basis of litigation between private parties and service providers such as landlords or exterminators. Such questions may include the appropriateness of certain pesticide treatments. Civil law actions and litigations involving athropods in dwelling or as house and garden pests are included in urban forensic entomology.[1] Sometimes used in stored products cases call in to help determine (chain of custody). Chain of custody is when you go back through all points of possible infestation to determine who is at fault.[2] Stored-product forensic entomology is often used in litigation over infestation or contamination of commercially distributed foods by insects.[1]

Medicolegal forensic entomology includes arthropod involvement in events such as murder, suicide, rape, physical abuse and contraband trafficking.[1] In murder investigations it deals with what insects lay eggs when and where, and in what order they appear in dead bodies. This can be helpful in determining the time or post mortem interval (PMI) and location of the death in question. Since many insects exhibit a degree of endemism (occurring only in certain places), or have a well-defined phenology (active only at a certain season, or time of day), their presence in association with other evidence can demonstrate potential links to times and locations where other events may have occurred (e.g., an Ohio man who claimed to have been in Ohio on the date his wife and children were murdered in California was found to have grasshoppers and other nocturnal insects from the west on his car grille, indicating that the car had been driven at night to the western US, and he was subsequently convicted[3]). Another area of medicolegal forensic entomology is the relatively new study of entomotoxicology. This particular branch involves the utilization of entomological specimens found at a scene in order to test for different drugs that may have possibly played a role in the death of the victim. The study of forensic entomology has not remained an esoteric science reserved only for entomologists and forensic scientists. The general public has become fascinated by this study and its applications since its beginning centuries ago

History

The concept of forensic entomology dates back to at least the 1300s but only in the last 30 years has it been systematically explored as a feasible source for evidence in criminal investigations. In history there have been several accounts of vague applications and experimentation of this science. There were many people who help lay the foundation of today’s forensic entomology. Sung Tz’u, Bergeret d’Arbois, Jean Pierre Mégnin and Reinhard were some of the biggest contributors to this science through their experiments and own interest about arthropods and death.

Sung Tz’u, a lawyer and death investigator in the late 13th century wrote a book commonly translated the “Washing Away of Wrongs” (洗冤集錄) in 1247 A.D. This book was to be used as a guide for other investigators so they could assess the scene of the crime efficiently. In this book he depicts several cases in which he took notes on how the person died and probable causes. He goes over in detail on how to examine a corpse both before and after burial. He also explains the process of how to determine the cause of death from murder to suffocation. His detail in explaining what he saw in all his cases laid down the fundamentals for forensic entomologists. This is the first recorded account of someone in history using this science for judicial means. [4]

In 1668, Italian physician Francesco Redi disproved the theory of "spontaneous generation", or abiogenesis. The accepted theory of Redi's day claimed that maggots developed spontaneously from rotting meat. In his experiment, he used samples of rotting meat that were either exposed to the air fully, partially, or not at all. Redi showed that the rotting meat that was fully and partially exposed to the air developed fly maggots, whereas the meat that was completely protected did not develop maggots. His discovery completely changed the way people viewed the decomposition of organisms and prompted further investigation into insect life cycles and into entomology in general.[5]


Dr Bergeret d’Arbois was a hospital physician who was the first to apply forensic entomology in a case report that included an estimation of postmortem interval (PMI). The 1855 report stated a general life cycle for insects and many assumptions about their mating habits. Yet he was the first to apply the new technique of PMI which gave the starting point to how this process is done. His main focus was not that of forensic entomology but rather using this subject more like a tool to prove his hypothesis of how the person and when the person died.[6]

The first systematic study in forensic entomology was conducted in 1881 by Reinhard, a German medical doctor who played a vital role in the history of forensic entomology. He exhumed many bodies and progressed the knowledge of what types of species can be tied to buried bodies. Reinhard conducted his first study in east Germany, and collected many Phorid flies from this initial study. He also concluded that not all the insects living with corpses underground were associated with them, since there were 15-year-old beetles who had little direct contact with them. Reinhard's works and studies were used extensively in further forensic entomology studies.

Another important figure is Jean Pierre Mégnin, an army veterinarian who published many articles and books on various subjects including the books Faune des Tombeaux and La Faune des Cadavres, which are considered to be among the most important forensic entomology books in history. [7] In his second book he did revolutionary work on the the theory of predictable waves, or succession of insects on corpses. By counting how many live and dead mites were developed each 15 days, and comparing this with his initial count on the infant, he was able to estimate how long that infant was dead.[8] In this book he asserted that exposed corpses were subject to eight successional waves whereas buried corpses were only subject to two waves. He had many great discoveries that helped shed light on the general characteristics of decaying flora and fauna. Mégnin's work and study of the larval and adult forms of insect families found in cadavers sparked the interest of future entomologists and encouraged more research in the link between arthropods and the deceased, and thereby helping create the discipline of forensic entomology.

Modern techniques

Many new techniques have been discovered and used in order to more accurately gather evidence, or possibly introduce an entire new way to look at old information. Over the years it has become more popular as case studies open doors to new ideas and techniques once though defunct, but now have proved to be invaluable in some courtroom battles. Forensic entomology not only uses arthropod biology, but it pulls from other sciences introducing fields like chemistry and genetics, exploiting their inherent synergy through the use of DNA in forensic entomology.

There are many techniques currently being developed to differentiate between the various species of forensically important insects. A study in 2007 demonstrates a technique that can use scanning electron microscopy to identify key morphological features of eggs and maggots. Some of the morphological differences that can help identify the different species are the presence/absence of anastomosis, the presence/absence of holes, and the shape and length of the median area. The ability to use these morphological differences gives forensic entomologists a powerful tool that can help with estimating a post mortem interval and with other relevant information. [9]

In 2001, a method was devised by Jeffery Wells and Felix Sperling to use mitochondrial DNA to differentiate between different species of the subfamily Chrysomyinae. This is particularly useful when working on determining the identity of specimens that do not have distinctive morphological characteristics at certain life stages. [10]

A valuable tool that is becoming very common in the training of forensic entomologists is the use of mock crime scenes with pig carcasses. The pig carcass represents a human body and can be used to illustrate various environmental effects on both arthropod succession and the estimate of the post mortem interval. [11]

Usually fly larvae are used to aid in the determination of a PMI. However, sometimes the body may not contain maggots and only the eggs are present. In order for the data to be useful the eggs must be identified down to a species level to get an accurate estimate for the PMI. There is more than one way to identify a fly egg by visual means. One method is called the scanning electron microscopic method (SEM). The SEM method provides an array of morphological features for use in identifying fly eggs; but, this method does have some disadvantages. The main one is that it requires expensive equipment and can take time to identify so it may not be useful in a field study or to quickly identify a particular egg.[12] This method is good if you have ample time and resources to determine the species of the particular fly egg. Sometimes that option is not viable, and a quicker and lower cost technique can be found in potassium permanganate staining. This process involves a few basic steps. Once the eggs intended to be stained are collected, they are rinsed with a normal saline solution and then moved to a glass petri dish. The eggs are then soaked in a 1% potassium permanganate solution for one minute. Then the eggs were dehydrated and mounted onto a slide for observation.[12] These slides can be used with any light microscope with a calibrated eyepiece to compare various morphological features. The most important and useful features observed for identifying eggs are things like the size, length, and width of the plastron, as well as the morphology of the plastron in the area around the micropyle.[12] The various measurements and observations are then compared to standards for forensically important species and used to determine the species of the egg.

Although physical characteristics and sizes at various instars have been used to estimate fly age, more recently a study has been conducted to determine the age of an egg based on the expression of particular genes. This is particularly useful in developmental stages that do not change in size, such as the egg or pupa, where only a general time interval can be estimated based on the duration of the particular developmental stage. This is done by breaking the stages down into smaller units separated by predictable changed in gene expression.[13] Three genes were measured in an experiment with Drosophila melanogaster: bicoid (bcd), slalom (sll), and chitin synthase (cs). These three genes were used because they are likely to be in varied levels during different times of the egg development process. These genes all share a linear relationship in regards to age of the egg; that is, the older the egg is the more of the particular gene is expressed. [13] However, all the genes are expressed in varying amounts. Different genes on different loci would need to be selected for another fly species. The genes expressions are mapped in a control sample to formulate a developmental chart of the gene expression at certain time intervals. This chart can then be compared to the measured values of gene expression to accurately predict the age of an egg to within two hours with a high confidence level.[13] Even though this technique can be used to estimate the age of an egg, the feasibility and legal acceptance of this must be considered for it to be a widely utilized forensic technique.[13] One benefit of this would be that it is like other DNA-based techniques so most labs would be equipped to conduct similar experiments without requiring new capital investment. This style of age determination is in the process of being used to more accurately find the age of the instars and pupa, however, it is much more complicated as there are more genes being expressed during these stages.[13] The hope is that through this, and other techniques similar to it, a more accurate PMI can be obtained.

Insects in forensic entomology

Further information: Decomposition, Forensic Entomology: Stages of Decomposition, and Insect development during morgue storage and autopsy procedures

There are many types of insects that can be involved in forensic entomology, but the ones listed here are mostly necrophagous (corpse-eating) and related to medicolegal entomology. This is not a full list; there are many variations due to climate, and many other insects that are necrophagous. This is outlined by Mostovski and Mansell.[14] The order in which the insects feed on the corpse is called the faunal succession.[15]

Flies (order diptera)

Flies are often first on the scene. They prefer a moist corpse for the maggots to feed on, as such a corpse is easier for them to chew. The most important families are:

Beetles (order coleoptera)

Beetles are generally found on the corpse when it is more decomposed. In drier conditions, the beetles can be replaced by moth flies (Psychodidae).

  • Rove Beetles - Family Staphylinidae - are elongate beetles with small elytra (wing covers) and large jaws. Like other beetles inhabiting carrion, they have fast larval development with only three larval stages. Creophilus species are common predators of carrion, and since they are large, are a very visible component of the fauna of corpses. Some adult Staphylinidae are early visitors to a corpse, feeding on larvae of all species of fly, including the later predatory fly larvae. They lay their eggs in the corpse, and the emerging larvae are also predators. Some species have a long development time in the egg, and are common only during the later stages of decomposition. Staphylinids can also tear open the pupal cases of flies, to sustain themselves at a corpse for long periods.
  • Hister Beetles - Family Histeridae. Adult histerids are usually shiny beetles (black or metallic-green) which have an introverted head. The carrion-feeding species only become active at night when they enter the maggot-infested part of the corpse to capture and devour their maggot prey. During daylight they hide under the corpse unless it is sufficiently decayed to enable them to hide inside it. They have fast larval development with only two larval stages. Among the first beetles to arrive at a corpse are Histeridae of the genus Saprinus. Saprinus adults feed on both the larvae and pupae of blowflies, although some have a preference for fresh pupae. The adults lay their eggs in the corpse, inhabiting it in the later stages of decay.
  • Carrion Beetles - Family Silphidae- The Behaviors: Adults tend to bury small carcasses underground to prepare for their young. Both parents tend to their young and exhibit communial breeding. Males job in care is to provide protection for the breed and carcass from competitors.

The biology: They feed on bodies decaying animals. Average size is about 12mm. They are also called burying beetles because they dig and bury small carcass underground..[16]

  • Skin/Hide Beetles - Family Dermestidae. Hide beetles are important in the final stages of decomposition of a carcass. The adults and larvae, which are hairy, feed on the dried skin, tendons and bone left by fly larvae. Hide beetles are the only beetle with the enzymes necessary for breaking down keratin, a protein component of hair.
  • Scarab Beetles - Family Scarabaeidae- Any of about 30,000 beetles that are compact, heavy-bodied and oval are found worldwide. In flattened plates, which each antenna terminates, are fitted together to form a club. Toothed or scalloped maybe on the outer edges of the front legs. They range from 0.2 to 4.8 in (5 to 120mm) long. These species are known as one of the heaviest insects. Since they have beautifully coloured, large, and hard, highly polished forewings, many are popular because of their insect collectors.[17]
Mites (class acari)

Many mites feed on corpses with Macrocheles mites common in the early stages of decomposition, while Tyroglyphidae and Oribatidae mites such as Rostrozetes feed on dry skin in the later stages of decomposition.

Nicrophorus beetles often carry on their bodies the mite Poecilochirus which feed on fly eggs. If they arrive at the corpse before any fly-eggs hatch into maggots, the first eggs are eaten and maggot development is delayed. This may lead to incorrect PMI estimates. Nicrophorus beetles find the ammonia excretions of blowfly maggots toxic, and the Poecilochirus mites, by keeping the maggot population low, allow Nicrophorus to occupy the corpse.

Moths (order lepidoptera)

Clothes-moths - Family Tineidae - feed on mammalian hair during their larval stages and may forage on any hair that remains. They are amongst the final animals contributing to the decomposition of a corpse.

Wasps, ants, and bees (order hymenoptera)

The insects in this group, order Hymenoptera, are not necessarily necrophagous. While some feed on the body, some are also predatory, and eat the insects feeding on the body. Bees and wasps have been seen feeding on the body during the early stages. This may cause problems for murder cases in which larval flies are used to estimate the post mortem interval since eggs and larvae on the body may have been consumed prior to the arrival on scene of investigators.

  • Wasps – (particularly) Family Vespidae- exhibit a range of social difficulty, from private living to eusocial colonies (a supportive group in which usually one female and several males are reproductively active and the nonbreeding creatures care for the young or defend and supply for the group) and thus are commendable for studies of the evolutionary origin and the social behavior in animals...[18]
  • Ants – Family Formicidae- Among the most widespread and damaging of introduced species are ants. Many ants share some characteristics that ease their preamble, institution, and subsequent range expansion. One feature of their importance is the ability to establish numerically large, ecologically dominant colonies.[19]

The South's warm and wet weather are ideal for imported fire ants. Fire ants colonies have blossomed in the prime grazing and crop land, along roadsides, and in parks and lawns. During 1940s and 1950s is when the most entensive and rapid spread of fire ants occurred.[20]

See also

Notes

  1. ^ a b c Catts, E. P. (1992). Annual Review of Entomology. 37: 253-272. doi:10.1146/annurev.en.37.010192.001345. {{cite journal}}: |access-date= requires |url= (help); Missing or empty |title= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help) Cite error: The named reference "Catts" was defined multiple times with different content (see the help page).
  2. ^ Bledsoe 2008, personal interview
  3. ^ "Insects help convict killer". Retrieved 2008-04-01.
  4. ^ S. Tz’u., B.E. Mc Knight 1981, The Washing Away Of Wrongs, Center for Chinese Studies The University of Michigan, Pages 1-34
  5. ^ "A History of Microbiology." Historique. 30 Apr. 2003. 12 Mar. 2008 <http://microbes.historique.net/history2.html>.
  6. ^ Benecke, M 2001, A brief history of forensic entomology. Forensic Science International, Volume 120, Issue 1-2, Pages 2-14
  7. ^ Volume 144, Issues 2-3, 10 September 2004, Pages 259-263 100th Anniversary of the German Society of Legal Medicine [1]
  8. ^ Forensic Science International Volume 120, Issues 1-2, 15 August 2001, Pages 2-14 [2]
  9. ^ Mendonça , Paloma Martins. "Identification of fly eggs using scanning electron microscopy for forensic investigations ." 2008. Micron. 13 Mar 2008
  10. ^ Wells, D. and Sperling Felix A. H. "DNA-based identification of forensically important Chrysomyinae (Diptera: Calliphoridae)"Forensic Science International Volume 120, Issues 1-215 Aug 2001 110-115 . 03 Mar 2008
  11. ^ Schoenly, Kenneth G. "Recreating Death's Acre in the School Yard: Using Pig Carcasses as Model" American Biology Teacher v68 n7 Sep 2006 402-410 . 03 Mar 2008
  12. ^ a b c Sukontason; et al. (2004). "Identification of Forensically Important Fly Eggs Using A Potassium Permanganate Staining Technique". Micron. 35 (5): 391–395. doi:10.1016/j.micron.2003.12.004. {{cite journal}}: |access-date= requires |url= (help); Cite has empty unknown parameter: |coauthors= (help); Explicit use of et al. in: |last= (help); Unknown parameter |month= ignored (help)
  13. ^ a b c d e Tarone, Aaron M. (2007). "Aging Blow Fly Eggs Using Gene Expression: A Feasibility Study". Journal of Forensic Sciences. 52 (6): 1350–1354. doi:10.1111/j.1556-4029.2007.00587.x. Retrieved 2008-04-01. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  14. ^ [3] (link not working as of 2008-03-23)
  15. ^ [4] (link not working as of 2008-03-23)
  16. ^ Scott, Michelle Pellissier (1998). Annual Review of Entomology. 43: 595-618. {{cite journal}}: |access-date= requires |url= (help); Cite has empty unknown parameter: |coauthors= (help); Missing or empty |title= (help); Unknown parameter |month= ignored (help)
  17. ^ unknown, www.encyclopedia.com/doc/1B1-377894.html
  18. ^ O'Donnell, Sean (1998). Annual Review of Entomology. 43: 323-346. doi:10.1146/annurev.ento.43.1.323. {{cite journal}}: |access-date= requires |url= (help); Cite has empty unknown parameter: |coauthors= (help); Missing or empty |title= (help); Unknown parameter |month= ignored (help)
  19. ^ Tsutsui, Neil D. (2003). "The Colony Structure and Population Biology of Invasive Ants". Conservation Biology. 17 (1): 48-58. doi:10.1046/j.1523-1739.2003.02018.x. {{cite journal}}: |access-date= requires |url= (help); Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  20. ^ Lofgren, C. S. (1975). Annual Review of Entomology. 20: 1-30. doi:10.1146 annurev.en.20.01075.000245. {{cite journal}}: |access-date= requires |url= (help); Check |doi= value (help); Missing or empty |title= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)

Further reading

  • Byrd, J. H. and J. L. Castner. "Forensic Entomology: The Utility of Arthropods in Legal Investigations". 2001. CRC Press. Boca Raton, FL. (ISBN 0-8493-8120-7)
  • Smith, K. G. V. 1986. A Manual of Forensic Entomology. Comstock Publishing Associates, Cornell Univ. Press, Ithaca, NY, 205 pp. (ISBN 0-8014-1927-1). A technical hardback designed for professional entomologists.
  • Catts, E. P. and N. H. Haskell, eds. 1990. Entomology & Death: A Procedural Guide. Joyce's Print Shop, Inc., Clemson, SC, xii + 182 pp. (ISBN 0-9628696-0-0) Spiralbound also aimed at professional entomologists, but shorter and with a popular style.
  • Greenberg, B. and Kunich, J.C., , 2002 Entomology and the Law: Flies as Forensic Indicators Cambridge University Press, Cambridge, United Kingdom 356 pp (ISBN 0-521-80915-0).
  • Leclerque , M. 1978 Entomologie médicale et Médecine légale Datation de la Mort, Masson ed. Paris, 112p
  • Nuorteva P 1977. Sarcosaprophagous insects as forensic indicators. In CG Tedeschi, WG Eckert & LG Tedeschi (eds), Forensic Medicine: a Study in Trauma and Environmental Hazards, Vol. II, WB Saunders, New York, p.1072-1095.
  • Goff, M.L. 2000. A fly for he prosecution: How insect evidence helps solve crimes. Harvard University Press, Cambridge, MA, 225p (ISBN 0-674-00220-2)
  • Liu, D.; Greenberg, B. 1989 Immature stages of some flies of forensic importance Annals of the Entomological Society of America 82(1):80-93.
  • Catts, E.P.; Goff, M. L. 1992 Forensic entomology in criminal investigations Annual Review of Entomlogy 37:253-272.
  • Wells, J.D. & Stevens, J.R. 2008 Application of DNA-Based Methods in Forensic Entomology. Annual Review of Entomology 53: 103-120.
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