The analysis of drugs and toxins in a body before death with the help of carrion-feeding insects is known as entomotoxicology. There has been a significant increase in deaths due to drug abuse and the scenario where a body found is highly decomposed is not uncommon. In such cases where there is no adequate amount of tissue available for toxicological analysis, the use of corpse-feeding insects, their larvae, puparial skin, etc. comes into effect. Necrophageous species such as Diptera, Coleoptera, and other arthropods can be used as reliable alternative specimens in death investigations. The major interest of the application of entomotoxicology is the determination of drug abuse just before death. This domain also focuses on the effect of drugs/toxins on insect development. This can assist in the estimation of post-mortem interval.

According to a comparative study, fly larvae provide better sensitivity in toxicological analysis than putrefied tissues. Several studies have established a possible connection between drug concentration of the substrate and various developmental stages of insects feeding on the substrate. Insects are homogenized and analyzed with the help of toxicological procedures such as GC, GC-MS, TLC, HPLC-MS, and Radio Immuno Assay. Drugs and toxins are taken by the person before death are introduced into the metabolism of carrion-feeding insects (Diptera) and larvae. This transfer is further carried out when beetles predate on the Diptera larvae hence, Coleoptera can also be sent for toxicological analysis.

Drug pharmacokinetics and life traits of insects

Drug pharmacokinetics depends upon the species’ developmental as well as feeding stage. Necrophageous species Diptera and Coleoptera being the first to colonize are important for entomotoxicological investigations. Flies have 3 larval stages in their development. As each larval stage differs in its feeding activity, the difference in drug concentrations is also observed. During the 3rd stage, the larva stops feeding after attaining maximum size and walks away to become a pupa, so larvae show higher drug concentration than pupa, but puparia are observed to be more reproducible.

1st generation puparia are a better drug concentration estimator than 2nd generation larvae in highly decomposed bodies.

Drug effect on insect development

When a toxin/drug’s rate of absorption surpasses its rate of elimination, it can be detected in the larvae. Studies have demonstrated the effects of cocaine (a stimulant) on the insect’s rate of development. After 36 hours of hatching, maggots start to develop more rapidly if they feed on the liver/spleen of rabbits administered with the lethal dose of cocaine. This acceleration in the development of larvae continues for 76 hours after hatching.

In the case of a 20-year-old woman whose body was found in the bloated stage, colonization of maggots of Lucilia sericata and Cynomyopsis cadaverine (Calliphoridae) was seen in the face and upper torso. Most of the maggots were 6-9 mm in length and showed a post-mortem interval of 7 days. Just a single maggot of length 17.7 mm was found from the nasopharyngeal area indicating a period of 3 weeks. Further investigations proved that the victim was a cocaine abuser and had snorted cocaine a short while before death.

Insect sampling

Normally, toxicologists would just collect some maggots from the corpse but this leads to high variability in drug detection. The insects are collected from, around, or under the body and from the crime scene. It should be kept in mind that in highly decomposed bodies, insects collected may be from a source other than the corpse. Additionally, the body site of the collection also holds importance. Insects collected from the different body-sites result in high variation in drug concentration because of the fact that a drug is distributed in the body according to its physicochemical properties, this leads to varying concentrations of drugs in different organs.

The best sites for sampling are internal organs (e.g. liver) and muscles.

Larvae/insects collected from different parts of the body are packed separately. Unfortunately, there are no guidelines about the minimum number of specimens that should be collected.

Analytical procedures

• However, there is no standard procedure for killing insects, their storage, and decontamination.
• These steps influence the result of the analysis. Larvae/ adult insects collected from the crime scenes are killed either by boiling or freezing and are stored at -20C or in 70% alcohol. In contrast, pupae are stored under dry conditions at -20 C. Samples are prepared for analysis after killing and decontamination. The sample preparation method will depend on the nature of the sample and on the drug of interest.
• In the case of solid specimens, they are first macerated and then homogenized or are dissolved by acid digestion. Past this, drug extraction is done by protein precipitation, solid-liquid extraction (SPE), liquid-liquid extraction (LLE). When the sample preparation process is complete, various drug detection/quantification techniques such as TLC, HPLC-MS, GC, and GC-MS are employed.
• The field of entomotoxicology is in its nascent stage and further researches are being carried out emphasizing bioaccumulation, insect metabolism of drugs, etc.

REFERENCES

• Introna, F.& Compobasso, C. P.& Goff, M. L. (2001). Entomotoxicology. Forensic Science International. 120 (1-2): 42-47. https://doi.org/10.1016/s0379-0738(01)00418-2
• Chophi, R. & Singh, R. (2019). Forensic Entomotoxicology: Current concepts, trends and challenges. Journal of Forensic and Legal Medicine.Vol.67: 28-36. https://doi.org/10.1016/j.jflm.2019.07.010
• Dayananda, R.& Kiran, J. (2013). Entomotoxicology. International Journal of Medical Toxicology and Forensic Medicine. Vol. 3(2): 71-74. https://doi.org/10.22037/ijmtfm.v3i2(spring).4068
• Gosselin, M.& Wille, S. M. & Fernandez, M. & Di Fazio, V.& Samyn, N. & De Boeck, G.& Bourel, B. (2011). Entomotoxicology, experimental set-up and interpretation for forensic toxicologists. Forensic Science International. Vol. 208(1-3), 1-9. https://doi.org/10.1016/j.forsciint.2010.12.015