PDC Test - Prosperous Pests
You can earn 0.25 PDC by passing the exam following this article, which has been approved for publication by NCRA's Council of the Academy of Professional Reporters.
The questions are based on the material in the article but some may require additional research. Send your answer sheet to NCRA's Continuing Education Office, 8224 Old Courthouse Road, Vienna, VA 22182, and enclose a check for $40 (member) or $50 (non-member) to cover the processing fee.
by Renée Cohen
Bugs may seem like a nuisance, but they actually contribute to the earth's ecosystems as they pollinate, eat, and recycle organic matter. Over two-thirds of all the known organisms on earth belong to the phylum Arthropoda or what are more commonly referred to as insects. Today's entomologists use technology in a variety of ways to study the phylum Arthropoda, which, literally translated, means jointed feet. In fact, it is the segmented nature of their bodies and feet that contribute to the success of these creatures found in all habitats on our planet.
The diversity and specialized nature of the arthropod appendages are responsible for a great variety of functions, including locomotion, feeding, sensing, reproduction, and defense. Insects tune into their environments with highly sensitive organs of sense as well as complex behaviors. The oldest insect fossils date back over 400 million years. Later when flight evolved, insects were able to escape from predators, find food and mates, and disperse to new habitats much faster than animals on legs, enabling them to continue to thrive.
Since the earth is predominantly an arthropod world, it is logical to expect that humans would be in contact with these creatures. Insects pollinate, eat other arthropods, eat living and dead plants and trees, living and dead vertebrates, and vertebrate dung and urine. The feature of arthropods, which is most important in forensic entomology, is that they are important carrion feeders; that is, they eat dead vertebrate bodies, including man. Thus they perform valuable recycling of organic matter in our ecosystem as well as producing toxicological evidence.
Forensic entomology is an area of expertise that has grown in prominence recently. It is the application of the study of insects and other arthropods to legal issues. Historically one of the earliest written references to using forensic entomology techniques dates back to China in the 1200s. At that time a murder was investigated by having all the villagers present their sickles to see which one attracted the insects, presumably due to remnants of flesh on the blade. An important murder was solved by knowledge and keen observation of insect activity. Modern day forensic entomology is used in events such as murders, suicides, and rapes, as well as contraband trafficking.
This age of an insect can be considered as an estimate of the time of death in a crime scene investigation. By knowing the stages of an insect's life, one can calculate when an egg was laid. In most cases, the death of the victim probably occurred before the eggs were laid. However, this period may be quite variable as it depends on temperature, time of day and season of year the death occurred, and whether the corpse was exposed or immersed in soil or water, among other considerations.
We know that after death a succession of fungi, bacteria, and animals will colonize a dead body. The substrate on which the body is lying will also change over time. Leakage of fluids from the dead body will lead to the disappearance of certain insects, and other insects will increase as time goes on. Examining the fauna at and around the body can aid a forensic entomologist in determining how long the body has been there. Insects can also be of assistance in establishing whether a corpse has been moved after death, by comparing the local fauna around the body and the fauna on the body. If there is a difference in the estimates and the analysis of the soil suggests a short postmortem interval (PMI) and the analysis of the body fauna suggests a longer PMI, one can suspect that the body has been moved.
As a general rule, insects will lay eggs on a corpse within two days of the corpse becoming available. In some instances, movement of suspects, goods, victims, or suspect vehicles can be traced with the assistance of insects. Insect parts may be captured in different car parts such as in radiators or tire treads. By identifying the insects found and plotting the distribution of each insect as well as the biology of each species, a forensic entomologist can describe the areas where the suspect has been. One example is a case history where the country of origin of cannabis was determined by the insects found in the cannabis container.
To make the most use of entomological evidence at a crime scene, an experienced and well trained forensic entomologist should do the collecting. The exact procedure at the crime scene varies with the type of habitat, but in general, the work of the forensic entomologist includes the following: Visual observation and notations at the scene; climatological data collection at the scene; collection of specimens from the body before body removal; collection of specimens from the surrounding area before removal of the remains; and collection of specimens from directly under and in close proximity to the remains after the body has been removed.
After the decay starts and the body begins to smell, different types of insects are attracted to the dead body. The insects that usually arrive first are the Diptera -- in particular, the blowflies or Calliphoridae, and the flesh flies or Sarcophagidae. The females will lay their eggs on the body, especially around the natural orifices such as the nose, eyes, ears, anus, penis, and vagina. If the body has wounds, the eggs are also laid there. Flesh flies do not lay eggs, but deposit larvae instead. After a short time, depending on species, the egg hatches into a small larvae. This larvae lives on the dead tissue and grows fast. After some time, the larva molts and reaches the second larval stage. Then it eats voraciously, and it molts again. When the larvae is fully grown, it becomes restless and begins to wander. It is now in its prepupal stage. The prepupae then molts into a pupae, but keeps the third larval skin, which becomes the so-called puparium. Typically it takes between one week and two weeks from the egg to the pupae stage. The exact time depends on the species and the temperature in the surroundings. Once the insect reaches adulthood, its primary function is to reproduce.
Sometimes dead bodies are found in concealed environments where blowflies have no access. If there are blowflies found, it means that the body has been moved. Some insects are heliophilic; that is, they prefer to lay their eggs on warm surfaces, which means that the body, most likely, was lying in a sunny spot. Other blowflies prefer shade. For example, the Lucilia species prefer sunlight; whereas, the Calliphora prefer more shady conditions. Synanthropic species, like the fly Calliphora vicina, thrive in urban areas; whereas, the nonsynanthropic variety, for example, Calliphora vomitoria, prefer rural areas.
Insects may live in what we perceive as a silent world, but as we look more closely at some of the physical characteristics and behavioral attributes of these creatures we call bugs, the unspoken world of insects resounds with interesting science. With more than a million creatures in this phylum, it is worth exploring their habitats and highly successful means of proliferating. Although some may think that bugs will inherit the earth, it could be said that they already own it.
Renée Cohen is a JCR Contributing Editor.
Campbell, N., Ed. Biology. Redwood City, The Benjamin/Cummings Publishing Co.: 1993.
1. What is PMI?
a) postmortem interval
b) postmortem incident
c) physical-mental index
d) procedure-material index
2. Carrion feeders
a) are plants
b) are mammals
c) are birds
d) eat dead vertebrate bodies
3. The insects that usually arrive first at the site of a dead body are:
4. The most abundant creatures on earth are:
5. The most common use of forensic entomology at crime scene investigations is:
a) cause of death
b) site of death
c) estimated time of death
d) life cycle studies
6. The earliest referenced use of forensic entomology occurred in China in approximately
7. Insects are one of humanity's chief competitors for food and fiber.
8. Arthropoda means
a) crooked feet
b) jointed feet
c) stiff feet
d) thorasic sac
9. Arthropods have appendages that are specialized in function, including
d) all of the above
10. The oldest insect fossil dates back to the Devonian period, which began 400 million years ago.
11. Flight is one key to the great success of insects.
12. As soon as they hatch, the main job of larva is to
b) eat and grow
d) all of the above
13.The primary function of adult insects is
d) none of the above
14. Bright colors of butterflies, as well as the odors of moths and the sound of crickets, contribute to which essential life function:
15. Insects are beneficial to humans as they
a) carry diseases
b) compete with humans for food
c) are treated with pesticides
d) carry out pollination
16. How long does it take for the blowfly pupae to develop from egg stage?
a) one to two weeks
b) two to three months
c) four to six weeks
d) a day or two
17. The blood recovered from the digestive tract of an insect can
a) damage the environment
b) yield valuable toxicological information
c) affect ambient temperature
d) be used for pollination
18. The Swedish naturalist who, in the 1750s, developed the system used for classifying plants and animals was
a) Albert Einstein
b) Thomas Edison
c) Vincent VanGogh
d) Carolus Linnaeus
19. All of the following are arthropods except
d) Calliphora vicina
20. Insects are not capable of complex behaviors.
|Answer Sheet for Prosperous Pests
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2. a b c d
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20. a b c d