What is Forensic Entomology?
It is the use of insect evidence to answer question pertaining to legal issues
Subfields of Forensic Entomology
Urban
Insects that infest human, their structure and
companion animals, and damage building such as termites, cockroach etc.
Stored Products
Insects that infest foodstuff stored in premises. E.g. flour beetles, drugstore beetles, grain beetles, Indian meal moth, fruit flies etc.
Medicolegal Entomology
Arthropods involvement in events such as murder, suicide, rape, physical abuse, contraband trafficking and movement of body
Application of Forensic Entomology can be used as
Determination of …
- Time of Colonization (TOC) or minimum-Post Mortem Interval (m-PMI)
- Cause of death (Entomotoxicology)
- Location of death
- Body relocation
- Site of injuries
- Negligence and torture
How to Determine the m-PMI?
- Duration of life cycle of the particular fly species
*Fly arrives at the corpse as soon as possible (approximately within 10 minutes)
*Fly starts to lay eggs/larvae in the orifices/wounds
*Larvae consume flesh of the dead body and go through the life cycle - Pattern of insect succession on the dead body
* insect succession is defined as a process of insect community development on disturbed or newly exposed sites.
* A cadaver is a very rich but ephemeral resource
* Insect colonization of a corpse occurs in a predictable sequence along the decompositional stages of corpse
* Volatile byproducts produced by microbial communities could act as signaling agents to attract or repel certain insects during the decomposition process
* Dimethyl trisulfide (DMTS) is the main volatile byproduct that attracts blowfly
Stages of Decomposition
- Fresh stage (Days 1-2) : Begins at death, ends when bloating is evident. Breakdown of protein and carbohydrates
- Bloated stage (Days 2-6): Gasses produced by anaerobic bacteria inflate the abdomen
- Active decay stage (Days 5-11): Insect activities very active. Abdominal wall breaks and carcass deflates
- Advance decay stage (Day 10-25): Insect activities are now slower, dispersal of maggots to drier places, some skin cartilage and bones are remaining on body
- Dry stage (Days 25+)- mainly bones and hair remains. Little or no odor. Can last several months to years
Determination of Cause of Death
- Poison can be traced in blood, urine, stomach contents, hair and nails
- Maggots collected from corpse can be utilized to detect drugs (e.g., suicide cases)
- Malathion (taken orally) may lead to delay in flies colonization at the mouth
Chemicals Traced from Maggots (HPLC)
- Triazolam - tranquilizer
- Oxazepam - treatment of anxiety and insomnia
- Alimemazine - acts as a sedative, hypnotic, and antiemetic for prevention of motion sickness
- Chloropriamine - treatment of allergic conjunctivitis, allergic rhinitis, bronchial asthma, and other atopic conditions
- Phenobarbital - treatment of certain types of epilepsy
- Malathion - pesticide
- Mercury
- Amitriptyline – treatment of major depressive disorder
- Nortriptyline - treat depression, neuropathic pain, attention deficit hyperactivity disorder, smoking cessation and anxiety
- Phencyclidines-hallucinogenicdrug
- Cocaine
- Heroine
Determination of Geographical Location of Death
- Some flies are rural species and do not exist in urban areas. Hence, presence of certain maggots on dead body shows the original location of the crime scene (primary crime scene)
Example: Some flies are specific to regions in Texas
Determination of Body Relocation
- Some fly larvae (Eristalis sp.) are only found in aquatic conditions. Presence of these maggots on corpse that was found on land indicated that the body has been moved
- Synthesiomyia nudiseta (Diptera: Muscidae) only lays eggs in indoor environment (inside the house). Presence of these maggots on dead body found outside the house indicated the body has been moved from indoor to outdoor
- Buried and then exhumed can be determined by the presence of phorid fly (Diptera: Phoridae) larvae
Determination of Site of Injury
- Fly larvae normally infest orifices of a corpse such as eyes, nostrils, ears, oral cavity and urogenital openings
- Infestation of fly larvae on uncommon places such as head and abdomen may indicate the site of injury due to opening wounds and blood smell
- Massive infestation of fly larvae on genital area indicated severe injury and this can be seen in most rape-murder cases
Determination of Negligence and Torture
- C. bezziana (A.k.a. screwworm fly or blow fly) does not infest dead tissue as it is an
obligatory myiasis agent. - Infestation indicates cutaneous myiasis, probably the deceased was tortured or neglected before death
Molecular Tools Used in Medical Entomology
- Drosophila melanogaster (fruit fly) has long served as a research model organism, providing insights into the fundamental mechanisms of development, neurobiology, genetics, species diversification, and genome evolution
Koch’s Postulates
- First, infected vectors must be associated with all cases of the same disease
- Second, the pathogen must be isolated and identified within the vector. Molecular or nonmolecular techniques are used to isolate and identify the pathogen, including its genotype, from suspected vectors. Genotypes should be identifcal to those in the infected host population
- Third, a naïve, noninfected vector must be able to acquire the pathogen from an infected host. The naïve vector must become infected with the same pathogen present in the infected host. Vector infection can be confirmed via standard or molecular techniques
- Fourth, the infected vector must transmit the pathogen to a naïve host and cause disease
Molecular Techniques
- Polymerase Chain Reaction (PCR) – Most common method for detecting the presence of pathogen. Used to detect pathogens harbored within a vector or host by specifically amplification of the targeted DNA with the used of target specific primers.
- Genetic data can be used in comparisons within and between phyla to identify the molecular basis for traits that are unique or shared across the tree of life, further defining evolutionary relationships (phylogenomics)
- At a finer scale, genome sequence availability enhances identification of single-base differences (SNPs) within and between arthropod populations (population genomics)
- The i5K insect genome sequencing initiative (http://i5k.github.io/) aims to sequence the genomes of 5,000 arthropods that are of agricultural and medical importantce
- The comparative genome analysis of 16 Anopheles mosquito species including representatives from broad geographical locations that occupy various ecological niches and have different vectorial capacities. This provides a means to understand why some species are more competent vectors of human malaria than others
Why sequence a gene or a genome?
Provide insight into the biology of an organism such as gene function, biochemical pathway, etc. Whole genome sequencing allows us to understand the genetic makeup of an organism.
The importance of house fly genome
The house fly genome has expanded immune system gene families encoding antimicrobial receptors and effectors, which is likely an adaptation to the septic niches and microbe-rich substrates in which they live and breed
Molecular Tools to Manipulate Arthropods
- After genes of interest are identified, researchers typically proceed to assess gene function in biological processes by altering these genes or their gene products. Then, observe the phenotypic result (reverse genetics)
- These genetically engineered or genetically modified organisms (GMOs) are generated by “knock out” (deletion of gene) or “knock in” (addition of gene) methods.
- Both methods either can be directed toward a certain region of the genome or random
What is the sterile insect technique (SIT)
The sterile insect technique (SIT) is a control strategy that uses radiation to produce genetic mutations or chromosomal breaks to generate sterile adult insects.These sterile insects are released into the wild to suppress and eventually eradicate wild pest populations
