Insect development during storage

Insect Development During Morgue Storage and Autopsy Procedures

Decomposition is a natural process of the body slowly dissipating over time. This process is aided by insects, making the bodies decompose at a faster rate. For forensic entomologists, it is important to carefully collect, preserve and analyze insects found near or on a victim. By doing that, they can provide an estimated time of death as well as the manner of death and the movement of the corpse from one site to another. The role of a forensic entomologist adjunction to the pathologist is to “collect and identify the arthropods associated with such cases and to analyze entomological data for interpreting insect evidence.” [Benecke]

History of Forensic Entomology

In The Washing Away of Wrongs, the first documented forensic entomology case was reported by Chinese lawyer and death investigator Sung Tz’u. In 1235 A.D., a stabbing occurred in a Chinese village. After further questioning, the investigator had all villagers bring their sickles and lay them out before the crowd. Blow flies were attracted to a single sickle because of invisible remnants of blood and tissue still adhered to it. The owner of the alleged sickle later broke down and confessed the crime. In other areas of the text, Sung Tz'u demonstrated knowledge of blow fly activity on bodies relative to those orifices infested, the time of infestation, and the effect of trauma on attractiveness of tissue to such insects. Later in France, 1855, forensic entomology was first used as a legal instrument in a court of law by Bergeret. By using the aggregation of insects on the corpse, he calculated the approximate time period that a mummified baby that was found behind a mantle. In the last three to four decades, medico-criminal entomology in post mortem research and investigation has been utilized and accepted as viable documentary proof in a number of case studies, especially in Canada, the United States, and Europe.

Autopsy Procedures

A crucial part of forensic investigations is autopsy procedures, which can be influenced by insect development during morgue storage. Bodies may have been stored in coolers or refrigeration units, for various time intervals, ranging from hours to days. Corpses are kept in two types of mortuary rooms: positive and negative temperature morgues. Temperature in a positive morgue ranges from +2°C to +4°C, which is the most common to keep the bodies for a few days or weeks. However, it does not prevent decomposition of the corpse. Negative temperature morgues have temperatures ranging from -15°C to -25°C. At this range, bodies are completely frozen and decomposition is altogether halted. For bodies that have not been identified, storing them in negative temperature morgues is customary.

Two main physiological responses to low temperature are diapause and quiescence. Diapause is a feature that insects use to synchronize their development within their life cycle with seasonal cycles of the environment. It has evolved to help insects respond to adverse environmental conditions by delaying their development. However, quiescence acts like an anesthetic, and stops insect development for a short time by slowing down insect metabolic activity. It is induced by a sudden drop in temperature that ranges from 0°C to 10°C. For example, a simulation of insects chilling in a morgue was conducted by using Calliphora vicina to illustrate that adult emergence is delayed by 24 hours, no matter in which stage the refrigeration occurred. There was no mortality when they were kept at 3°C for 24 hours. In this simulation, quiescence was induced by the low temperature and the insect physiology was not affected when they were returned to 24°C.

Body parts with high temperatures have the greatest tissue loss from immense maggot masses. There can be extensive tissue loss in a morgue by how many maggots are present on the body and how long the body is kept in the morgue. When calculating the post mortem interval (PMI) at the autopsy, it is important to note the temperatures of the maggot masses when gathering the maggots from the body. The temperature of maggot masses in a cooler slowly decreases, which gives the minimal temperature the maggots can encounter. There may be little or no effect of the lower temperatures on insect development if the maggot mass was well established before placing the body in the cooler. In calculating the degree-days and the life cycle from one stage to another, it is important to note how many maggots are on the body, what type of species it is due to different developmental thresholds, and the temperature and time in the cooler. For instance, the development of bluebottle blowflies is suspended at 3°C, the common temperature of a morgue’s cold storage chamber.

Despite the result from the Calliphora vicina experimental study, refrigeration could affect PMI calculation because it may cause physiological disturbances in certain insect species. However, this refrigeration process must be done if the insects collected at the crime scene cannot be sent to a forensic entomologist immediately. Because insect development could advance after the refrigeration period, it could lead to an underestimation of the time of death.

Maggots develop at a rate that is depended entirely upon environmental factors, which makes temperature one of the most important things throughout the morgue evaluation process. Insects that are cold tolerant or warm tolerant, will have different temperatures in the body bag. Both cold and warm tolerant maggots survive by maggot mass feeding. However, cold tolerant maggots can develop in smaller masses while warm tolerant maggots require larger masses. The maggots produce metabolic heat from bacterial digestion of the flesh, which enables them to develop while stored in a cold location. Maggot masses tend to move to thicker parts of the body that decrease in temperature less slowly. This is sufficient to continue maggot development.

Occasionally, when a corpse is significantly infested with insects, the exterior of the bag will consist of larvae and other adult insects. Every surface of the bag, especially the inside corners, must be carefully examined for insects that may have moved away from the body due to change in temperature when the body was removed from the death scene. It is critical that the entomologist work quickly and efficiently during the autopsy to prevent further insect development throughout the body. This will assist in calculating a correct PMI. If clothing is found on the corpse, it is gathered and evaluated for insect evidence that is then photographed with macro lenses. As the insects are gathered, a record is to be kept that explains which location of the body insects were found. This is essential when insect sampling is delayed until the time of autopsy. Therefore it is useful to compare crime scene photos to the autopsy photos, to see changes that occurred within that time frame.

Although autopsy is typically thought of as a horrific disfigurement of the human body, it is actually an adequate procedure capable of determining a legitimate PMI, assuring medical conditions, and assisting in justifying a case that may have involved violent crime. During an autopsy various tasks and procedures must take place, as well as proper collection of entomological evidence. Entomological evidence is usually gathered at the crime scene while the body is in situ. This allows for a much more accurate estimation of the time of death. If the entomological evidence is not gathered before the body is removed, then the evidence may be collected at the time of the autopsy by an entomologist or a medical examiner. Certain insects and their life stages, within the corpse, are examined to estimate the time of death of the individual. It is critical to specify the immature stages prior to rearing them or refrigerating the body because low temperature has different effects on various stages of immaturity. A study on the effects of refrigeration on the biometry and development of Protophormia terraenovae shows that “10 days of refrigeration induced a decrease of the total developmental time of 56 and 18 hours for L1 [first stage larvae] and pre-pupae and an increase of 15 hours for L2 [second stage larvae]” [source#].

Forensic entomology has gained a strong legitimacy in recent years for introducing vital evidence into investigations worldwide. Without the collection and preservation of insects, associated with a death scene, we could not properly estimate the time of death as well as other valuable information concerning the circumstances of the body. Human corpses, no matter the manner of death, are aided by insect decomposers. This makes the storage of the body prior to the autopsy, a vital step in the field of forensics.

Benecke, Mark. (2001). A Brief History of Forensic Entomology. Forensic Science International, Vol. 120, p. 2-14. http://wiki.benecke.com/index.php?title=2001_Mark_Benecke:_A_Brief_History_of_Forensic_Entomology

Huntington, Timothy E. (2007). Maggot Development During Morgue Storage and Its Effect on Estimating the Post-Mortem Interval. Journal of Forensic Sciences, Vol. 52 Issue 2: 453-458.