Forensic entomology

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. 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. [2] 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])

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 (directly related to the crime and found on the corpse). 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 [4]. The order in which the insects feed on the corpse is called the faunal succession [5].

Insects of forensic importance

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:

• Blowflies - Family Calliphoridae
• Fleshflies - Family Sarcophagidae
• House Flies - Family Muscidae
• Cheese Flies - Family Piophilidae
• Coffin Flies - Family Phoridae
• Lesser Corpse Flies - Family Sphaeroceridae
• Lesser House Flies - Family Fanniidae
• Black scavenger flies - Sepsidae
• Sun Flies- Heleomyzidae
• Black soldier fly- Stratiomyidae

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
• Ham Beetles - Family Cleridae
• Carcass Beetles - Family Trogidae

• 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
• Sap beetles - Family Nitidulidae

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
• Ants – Family Formicidae
• Bees - Superfamily Apoidea

Books on forensic entomology

• Byrd, J. H. and J. L. Castner. "Forensic Entomology: Insects 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)

Other Literature

• 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.

History

Historically Important People in Forensic Entomology

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 exhumated 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 underground were associated with the corpses, since there where 15 year old beetles who had little direct contact with them. Reinhards' works and studies were used extensively in further Forensic Entomology studies.

Another important figure is Pierre Mégnin, who was an army veterinarian who published many articles and books on various subjects and two important forensic entomology books Faune des Tombeaux and La Faune des Cadavres which include many of his own personal cases. 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 baby, he was able to estimate how long that baby was dead. In this book he asserted that exposed corspes were subject to 8 successional waves whereas buried corpses were only subject to 2 waves. He had many great discoveries that helped shed light on the general characteristics of decaying flora and fuana. His works were also important because he increased the popularity and interest in Forensic Entomology.

Advancements in Forensic Entomology

Usually fly larvae are used to aid in the determination of a postmortem interval (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; however, this method does have some disadvantages. The main one being that it requires expensive equipment and can take time to identity so it may not be useful in a field study or to quickly identify a particular egg. This method is good if you have ample time and resources to determine the species of the particular fly egg. However, sometimes that option is not viable and the potassium permanganate staining method can be used. Once the eggs 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. 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. The various measurements and observations are then compared to standards for forensically important species and used to determine the species of the egg. The benefits of this are the speed and low cost at which it can be performed.

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. Three genes were measured in an experiment with Drosophila melanogaster: bicoid (bcd), slalom (sll), and chitin synthase (cs). They were chosen because they are likely to be in varied levels during different times of the egg development at different times. 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. 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. 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. The hope is that through this, and other techniques similar to it, a more accurate PMI can be obtained.

See also

• Decomposition
• Myiasis, important in legal proceedings where neglect is alleged
• Entomology and the Law Legal procedures

External links

Please note - these sites may contain strong graphic images and descriptions.

• Template:Dmoz
• www.forensic-entomology.com
• European Association for Forensic Entomology homepage
• Easily understood outline of Forensic Entomology
• Collection of original articles about Forensic Entomology. Many downloadable illustrated pdf's of cases
• Institute of Forensic Entomology Vienna Click on the pictures for enlargements and graphs
• What happens to the body after death
• Pastoral putrefaction down on the Body Farm: Autopsy, HBO Documentaries
• Dating Death Great Moments of Science
• DNA techniques for forensic entomology
• pdf about forensic entomology Deon Canyon
• Forensic Entomology page from Australia (Ian Dadour)
• Visible Proofs Beautifully designed site.The life cycle of the bowfly. Follow the not so clear Next arrow at the bottom right of each page
• Medical Zoology Pages
• Survey on carrion-visiting beetles – Research into the fauna of carrion-visiting beetles in Erlangen, Bavaria (2006): Carrion is an ecosystem of its own. Diverse species of beetles – belonging to different guilds – arrive and depart from carrion at different times – succession occurs. The arrival time and growth rates of beetles inhabiting corpses depending on weather, location and type of carrion have been studied.
• Forensic Entomology the next step (ForensicWiki)