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DNA Barcoding Workflow

Posted in Forensic Entomology & DNA Barcoding by paibiopai on March 28, 2011

Species identification through barcoding is usually achieved by the retrieval of a short DNA sequence – the ‘barcode’ – from a standard part of the genome (i.e. a specific gene region) from the specimen under investigation. The barcode sequence from each unknown specimen is then compared with a library of reference barcode sequences derived from individuals of known identity. A specimen is identified if its sequence closely matches one in the barcode library. Otherwise, the new record can lead to a novel barcode sequence for a given species (i.e. a new haplotype or geographical variant), or it can suggest the existence of a newly encountered species.

Various gene regions have been employed for species-level biosystematics, however, DNA barcoding advocates the adoption of a ‘global standard’, and a 650-base fragment of the 50 end of the mitochondrial gene cytochrome c oxidase I (COI, cox1) has gained designation as the barcode region for animals. This fragmentsize has been selected so that a reliable sequence read can be obtained by a single sequence pass in conventional cycle sequencing platforms. Shorter fragments of COI have also been shown to be effective for the identification of specimens with degraded DNA, however, where a 650-base sequence is not easily obtainable. In addition, the usability and robustness of COI in a standard highthroughput barcoding analysis have been extensively assessed.

Other researchers have suggested that alternate loci might also serve as a basis for species identification. For example, (more…)

Entomotoxicology: Insects as Toxicological Indicators and the Impact of Drugs and Toxins on Insect Development

Posted in Forensic Entomology & DNA Barcoding by paibiopai on January 23, 2011

Careful analyses of the community of insects encountered on a decomposing body, combined with knowledge of insect biology, ecology, and local environmental conditions can often provide valuable forensic insights. These can include the estimation of time since death, movement of the remains after death, indication of antemortem injuries, and the presence of drugs or toxins.
Over the past 2 decades, there has been an apparent increase in the incidence of drug related deaths reported within the U.S. and other countries. Decedents in such cases are, in many instances, not discovered for a substantial period of time (days or weeks). The
resulting state of advanced decomposition and environmental recycling typically encountered in these situations often dictates the employment of various entomological methodologies. The entomological techniques most frequently utilized are based on comprehensive analyses of the insects and other arthropods associated with (more…)

insects could determine human’s time of death

Posted in Forensic Entomology & DNA Barcoding by paibiopai on December 29, 2010

Insects are usually the first organisms to arrive on a body after death, and they colonize in a predictable sequence. A corpse, whether human or animal, is a large food resource for a great many creatures and supports a large and rapidly changing fauna as it decomposes. The body progresses through a recognized sequence of decompositional stages, from fresh to skeletal, over time. During this decomposition, it goes through dramatic physical, biological and chemical changes (Coe and Curran, 1980; Henssge  et al., 1995; Van den Oever, 1976). Each of these stages of decomposition is attractive to a different group of sarcosaprophagous arthropods, primarily insects. Some are attracted directly by the corpse, which is used as food or an oviposition medium, whereas other species are attracted by the large aggregation of other insects they use as a food resource.

When the sequence of insects colonizing carrion is known for a given area and set of circumstances, an analysis of  (more…)

If only death people could talk,,

Posted in Forensic Entomology & DNA Barcoding by paibiopai on December 15, 2009

“The body and the decomposers are telling you what happened, If you can only understand the language.”

-Lord and Rodriguez (1989)

Since the inception of human species, man has tried to dominate this planet by sheer intelligence. This dominance led to the concept of noosphere and he started interfering with natural processes. But nature has her own ways and one of its finest intricacies is the food web i.e. the process of eating and being eaten. This cycle is so immaculate that even dead bodies of animals, including that of humans, are decomposed by other creatures with insects playing a predominant role. And who knew that one day these so called natural scavengers would act as witness to man’s mud-paddling strategies for personal ambitions, jealousy and gains. Practical use of these organisms in solving crime led to the development of a separate branch of science now-a-days known as Forensic Entomology. (more…)

Corpse Fauna -Life Cycle of Flies- (siklus hidup lalat)

Posted in Forensic Entomology & DNA Barcoding by paibiopai on December 10, 2009

for further details, click below .. (more…)

What information can a forensic entomologist provide at the death scene?

Posted in Forensic Entomology & DNA Barcoding by paibiopai on November 23, 2009

Forensic entomologists are commonly called upon to determine the postmortem interval or “time since death” in homicide investigations.  More specifically, the forensic entomologist estimates a portion of the postmortem interval based on the age of the insect present.  This entomological based estimation is most commonly called the “Time Since Colonization”.  Based on the factors in a particular investigation, this may, or may not, closely approximate the entire postmortem interval.  In either case, it is the duty of the Forensic Pathologist, Medical Examiner, or Coroner to estimate the postmortem interval, and the Forensic Entomologist may assist them in providing information on the “time since colonization”, which can ultimately be used to substantiate a portion of the postmortem interval.

The forensic entomologist can use a number of different techniques including species succession, larval weight, larval length, and a more technical method known as the accumulated degree hour technique which can be very precise if the necessary data is available.  A qualified forensic entomologist can also make inferences as to possible postmortem movement of a corpse.  Some flies prefer specific habitats such as a distinct preference for laying their eggs in an outdoor or indoor environment.   Flies can also exhibit preferences for carcasses in shade or sunlit conditions of the (more…)

Common Insects found as Entomological Evidence -forensic entomology-

Posted in Forensic Entomology & DNA Barcoding by paibiopai on November 23, 2009

Acari

The Acari, or mites as they also are called, are small organisms, usually less than a mm in length. Mites occur under the dead body in the soil, during the later stages of decay. Many mites are transported to the body via other insects, such as flies or beetles. Other mites are soil dwelling forms which can be predators, fungus feeders or detritus feeders. Most species will be found in soil samples from seepage area under the body.

Aranea

The Aranea or spiders are predators on insects occurring on bodies. No species is specific to the carrion fauna, and will have limited or no value in estimation of the PMI.

Diptera

The order diptera contains insects with one pair of wings, the second ones modified to halteres. About 100,000 species are known to science, many more awaits discovery. Among the flies we find many members of the carrion fauna. The larvae of flies lives in very different habitats, also aquatic.

 

 

 

 

 

NEMATOCERA

Trichoceridae

Trichocera sp.

or winter-gnats as they also are called because the common species Trichocera regelationis, T. saltator, T. maculipennis, etc, fly abundantly in the winter months, although they occur at lower frequencies throughout the year. The adults resemble small crane-flies. The larvae are saprophagous and feed on decaying material. Trichocerid larvae constitutes an important part of the carrion fauna during the winter months, when the blowfly fauna are missing.

BRACHYCERA

Stratiomyidae

Larvae of Hermetia illucens is recorded eating on human excrement and human remains. Usually this species occur late in the decomposing process

(more…)

Using forensic entomology to determine whether the body has been moved after death

Posted in Forensic Entomology & DNA Barcoding by paibiopai on November 23, 2009

After death, a succession of fungi, bacteria and animals will colonize the dead body. The substrate on which the body is lying will also change over time. Leakage of fluids from the dead body will lead to the disappearance of certain insects, and other insects will increase as the time goes. A forensic entomologist can then look for how long the body has been there by looking at the fauna at the body, and also estimate the time the body has been lying there by sampling soil insects underneath the dead body. If there is a difference in the estimates, and the analysis of the soil suggests a short PMI, and the analysis of the body fauna suggests (more…)

Finding the Cause of Death using Forensic Entomology

Posted in Forensic Entomology & DNA Barcoding by paibiopai on November 20, 2009

In a crime investigation, there is not only of great interest to find out when a victim died, but also of interest to find out how the victim died, as this can be used to find the killer.

In some instances the insects themselves are the killers, in other instances the insects occuring on the carrion can shed a light on what happened when the victim died.

Wasps and bees, for example, can inject venom through a sting. Some people are sensitive and allergic to these venoms, and can die if not treated in time. One other important aspect of wasps and bees are their effect on drivers. Many car accidents are probably caused by some wasp, bee or bumble-bee coming through the window, causing hysteria, or a distraction from the road leading to a collision or other accidents. In some cases wasps and bees has been used as murder weapons,  (more…)

Estimating Time of Death with Forensic Entomology

Posted in Forensic Entomology & DNA Barcoding by paibiopai on November 20, 2009

After the initial decay, and the body begins to smell, different types of insects are attracted to the dead body. The insects that usually arrives first is the Diptera, in particular the blow flies or Calliphoridae and the flesh flies or Sarcophagidae.

The females will lay their eggs on the body, especially around the natural orifices such as the nose, eyes(2), and ears(2). If the body has wounds the eggs are also laid in such. Flesh flies do not lay eggs, but deposits larvae instead.

After some short time, depending on species, the egg hatches into a small larvae. This larvae lives on the dead tissue and grows fast. After a little time the larva molts, and reaches the second larval instar. Then it eats very much, and it molts to its third instar. When the larvae is fully grown it becomes restless and begins to wander. It is now in its prepupal stage. The prepupae then molts into a pupae, but keeps the third larval instars skin, which becomes the so-called puparium. Typically it takes between one week and two weeks from the egg to the pupae stage. The exact time depends on the species and the temperature in the surroundings.

The theory behind estimating time of death, or rather the post mortem interval (PMI for short) (more…)

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