History of forensic entomology

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.