An Introduction to Forensic Entomology Dead men do

An Introduction to Forensic Entomology Dead men do tell tales……

What is Forensic Entomology? l Application of insects to legal issues. l Medicocriminal forensic entomology. l Arthropods associated with crimes l Usually violent crimes such as murder, suicide, and rape, l Physical abuse and contraband trafficking. l Death investigations l Establishing timelines (time since death to time of discovery (postmortem interval or PMI) l Movement of the corpse, manner and cause of death. l Association of suspects with the death scene l Detection of toxins or drugs insect larvae

Succession l l l A cadaver is a very rich but ephemeral (shortlived) resource There is tremendous competition among organisms, especially in the early stages of decomposition. Insect colonization of a corpse occurs in a series of stages. l l Different groups are adapted to different decompositional stages of a corpse. Thus, there is a fairly predictable sequence of colonization

Stages of Decomposition l A. Fresh Stage (Days 1 -2) l l B. Bloated Stage (Day 2 -6) l l Abdominal wall breaks allowing gasses to escape. Carcass deflates. D. Post-decay Stage (Days 10 -25) l l Putrefaction begins. Gasses produced by anaerobic bacteria inflate the abdomen. C. Decay Stage (Days 5 -11) l l Commences at death, ends when bloating is first evident. Breakdown of protein and carbohydrates into simpler compounds In dry habitats, remains are skin, cartilage, and bones. In wet habitats, wet, viscous material in the soil under the remains. E. Dry Stage (Days 25+) l Mainly bones and hair remain. Odor is primarily that of normal soil and litter. Can last several months to years.

Major Groups of Insects Associated with Cadavers l Flies l l l Blowflies Flesh Flies House Flies Cheese Skippers Beetles l l l Carrion Beetles Dermestids Scarab Beetles

Blue Bottle Flies (Blow flies) Family name: Calliphoridae • Blowflies often are an attractive blue-green, metallic color, leading to the common English names, blue-bottles and greenbottles. • They also come in a nonmetallic, brown form, but all blowflies usually relatively large flies.

Green Bottle Flies (Blow flies) Family name: Calliphoridae Blowflies can pick up faint traces of the odor of decay from up to 20 km away and lay their eggs in a suitable corpse. Blow flies are one of the first insects to arrive at a cadaver – they prefer fresh, moist flesh.

Common House Flies Family name: Muscidae • Adults are most common at corpses in the early stages of decomposition when the corpse is moist. • The larvae are usually dung feeders.

Flesh Flies Family name: Sarcophagidae Most flesh flies breed in dead animals, dung, or decaying material, but a few species lay their eggs in the open wounds of mammals; hence their common name.

The Story Maggots Tell l l Blowfly maggots are of two forms: smooth maggots, and 'hairy' maggots. The smooth maggots belong to pioneer flies that are purely corpse feeders. 'Hairy' maggots will often feed on corpses, but they are also active predators that feed on smooth maggots. Because they are predators, the arrival of the secondary flies that produce hairy maggots is normally later than that of the pioneer maggots. Beetle maggots also tend to be predatory like the adult beetles.

Life cycle of the black blow fly l l l Adult female blow flies arrive within minutes to lay eggs on a cadaver. Each deposits about 250 eggs in the natural openings of the body and open wounds. The eggs hatch into first-stage maggots within 24 hours. These feed and then molt into second-stage maggots, which feed for several hours, and then molt into third-stage maggots. Masses of third-stage maggots may produce heat, which can raise the temperature around them more than 10° C. After more feeding, the third-stage maggots move away from the body and metamorphize into adult flies.

General Life cycle of Beetles l l l l A single female may lay from several dozen to several thousand eggs during her lifetime. Eggs can be laid singly or in clumps Larva feed voraciously – they can be predatory. The larval period varies between species but can be as long as several years. All beetle larvae go through several instars, which are the developmental stages between each molt. In many species the larvae simply increase in size with each successive instar as more food is consumed. In some cases, however, more dramatic changes occur. beetle larvae pupate, and from this pupa emerges a fully formed, sexually mature adult beetle, or imago. Adults have an extremely variable lifespan, from weeks to years, depending on the species.

Succession Fresh 1 Decay 4 2 Post-Decay 5 Bloated 3 Dry 6

Post-Mortem Interval (PMI) l l l Elapsed time from a death to the discovery of a cadaver. Flies (especially calliphorids and sarcophagids) can be vital in determining the PMI Premises l l l Flies will begin oviposition as soon as they discover a body Succession on a corpse is predictable Insect development is predictable

Fly development l l l Fly development is structured into stages Each stage requires a certain amount of time Time to complete a stage is temperature dependent. At warmer temperatures the rate of development is fast, at cool temperatures it slows down Each species has a certain developmental rate at any given temperature

Temperature Effects on Insect Growth • How do we measure insect growth? • Linear approach Upper Threshold Lower Threshold

Insect development l Temperature and time

Degree-Day Accumulation l Using a simple formula to calculate degree-day accumulation for a species with a 10 C threshold If max or min is less than 10, then enter zero A B C D E

Temperature-Dependent Development of Flies

Determining PMI l l Two different ways to use collected data in PMI determination l The isomegalen diagram l Controlled rearing Situation dictates which is best solution

Isomegalen Diagram for Phaenicia (= Lucilia) sericata 8 mm maggot 24 C daily max. 16 C daily min. 8

Controlled rearing l l l Collect sample from crime scene Rear until adults eclose under constant conditions in the lab. Determine the ADD (or ADH) required to complete development after collection Subtract this value from the total required for the species to determine unknown amount accumulated since oviposition Count back the days (or hours) prior to collection necessary for the maggot to reach the stage at which it was sampled

Data for Controlled Rearing Species Lower Threshold ( C) ADH ADD Phaenicia sericata 10 4140 - 5812 173 - 242 Phormia regina 10 4038 - 6100 168 - 254 Calliphora vomitoria 6 17678 737 Cynomyopsis cadaverina 6 5511 379 Complete lifecycle: egg-adult Unknown portion Known portion Total for the species

Determining the PMI l Step 1. Collect samples of the insects present. l l Air temperature for general area (airport readings, validate with micro data -loggers). Look for ‘windows’ of insect opportunity Step 3. Estimate time of egg laying l l Representative samples of other maggots present. Preserve some immediately. Rear others to adulthood to confirm species ID’s Step 2. Determine temperature history at crime scene l l Critical to collect the largest maggots on the cadaver, even if they are few. Given the species present and their age (size), how long did it take them to develop to that point at the temperatures occurring in the area. Step 4. What other insect evidence is available? l Look for other insect evidence that might corroborate or contradict your PMI estimate.

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