A. B. N. Seal College
Mysterious and unnatural criminal cases are accelerated significantly in past decades around the
globe. Nowadays, suicides and intentional crimes have become front page information in a number
of online news portals. To unmask the timing, reason and sites of mysterious deaths, legal agencies
are using several branches of biomedical sciences. Among them forensic entomology, though less
known but is the more relevant one. Forensic entomology deals with the study of morphology, life
cycle, behavior and molecular architecture of insects that colonize on dead bodies of human and
other animals. Such a study can be of great value for crime scene scientists and other legal agencies
in saving time and ruling out the cause and time since death. When the time of death has exceeded
more than 72 hours, entomological time line becomes an integral part of death investigations.
Insects belong to a vastly abundant taxa and are both land and aquatic inhabitants. Different insect
species have a unique timeline for development of stages such as egg, larva, pupa and adult. Eggs
after certain period hatch out into larvae. The intermediate developmental stages of larvae are
described as instars. The post feeding larvae isolate themselves into the soil to convert themselves
into pupae. The last metamorphosed stage is the adult that emerge out from the pupal sheath by a
process of eclosion. In forensic entomology, various developmental stages and respective
durations are usually represented through isomegalen and isomorphen plots.
Adult insects have an amazing sense of smell that enables them to detect food sources. Hidden dead bodies escape the sight of human beings but flesh-eating insects can precisely localize the site owing to the smell of gases and organic fluids. Insects lay eggs on decomposing bodies and thereafter they run the cycle of development. Since the developmental durations are of fixed periods, their identification provides the clue for time, reason and site of the crime.
Flesh eating Insects and Entomological post mortem interval:
Fresh dead matter attracts Blow flies (family: Calliphoridae) mainly in the first 3 months. They lay eggs that resemble rice particles. Dead body when it starts to putrefy, releases a pungent smell in the first couple of months that attracts flesh flies (family: Sarcophagidae). If the fat goes rancid in the dead organic matter in next 3-6 months, it keeps on attracting Dermestid beetles (family: Dermestidae). Mites can also be recovered in 1-12 months. If the dead remains go completely dry in 1-3 years, there is still the possibility to discover Dermestid beetles, which are found even after 3 years of death. Therefore, identifying these species and their developmental stages can provide clues regarding the post mortem interval in case of mysterious deaths.
Biotechnology aids accuracy in forensic entomology
Until the 20th century, studies were limited to the traditional morphological identification of insects with relevance to their predictable life cycles according to their class, order and species that made entomology lengthy and time-consuming in forensics. But fortunately, with advancement in biotechnology, forensic entomological data have become more realistic and reliable. DNA typing and barcoding techniques led to accurate identification of insect species and therefore encouraged legal investigators to rely on entomological data more than in previous times.
Species identification is carried out using certain genetic markers such as STRs and minisatellite DNA. The non-repetitive sites on mtDNA are the promising targets for species identification. Moreover, study on differential gene expression can help to predict the ages of insects on dead bodies. Expression of genes like bicoid, slalom and chitin synthase help to unravel the correct developmental stages.
Age of larvae can be estimated through naked eyes but that for pupal stage is not possible. Interestingly, with the help of real time PCR, differential expression of two genes viz. actin and arylphorin receptors can be evaluated. Expressions of these genes are age dependent and therefore useful in predicting pupal age on corpses. Moreover, cuticle contains hydrocarbons whose chemical composition alters with age. These alterations can be monitored through gas chromatography to determine age of larvae, pupae and adults. In addition, cytochrome oxidase subunits 1 and 2 are actively used to identify species of flesh-eating insects.
Entomological time line is very useful in determining post mortem interval, site, circumstances and causes of unnatural/mysterious deaths. Study at the molecular level can help to congregate more accurate and reliable data for forensic investigations.