NCSU ENT 305 Exam 1 study guide

Forensic Entomology

A small discipline: The study of insects and other arthropods that interact with legal matters

•Urban: legal proceedings concerning insects that affect man-made structures (termites, cockroaches)

•Stored Products: legal proceedings involving insects infesting stored commodities

•Medicolegal (Forensic medical entomology): involves the utility of arthropod evidence in solving crimes or unexplained death

Scope and Applications of Medico-Legal Forensic Entomology

▪Unexplained death:

▪Determination of death location

▪Placement of body after death

▪Detection of drugs and toxins in remains through insect analysis

▪Estimate postmortem interval

▪Neglect of children and elderly

Criminal misuse of insects

Early Homicide Investigation

•For most of western history this involved little more than finding some degenerate looking individual and pinning the crime on them

This usually included torture for a confession

Chinese Forensic Science

•In the West, murder was never associated with flies until mid-nineteenth century

•The earliest recorded applications of forensic entomology were by the Chinese

•Crime set in ~930 AD: An officer of the court suddenly heard a woman wail. The officer asked her what happened. The woman said her husband was killed by fire, but the officer discovered many flies clustered on the head of the corpse. At autopsy, there was a snag in the head of the corpse. The woman confessed that she and another man had attacked the head of her husband.

Sung Tzu book

Sung Tz'u's famous book "Washing Away of Wrongs" describes various levels of decomposition along with seasonal variations

This book was translated and disseminated throughout Asia and became the standard text for forensic investigations until the 19th century

•The book describes a slashed and bloodied victim on a sweltering hot summer day

•The investigator demanded all the bladed tools be brought to him

•Flies then collected on the murder weapon

•One of 1st to mention the use of flies in determining a criminal case

eighteenth century case china

A third documented case occurred in the eighteenth century:

A merchant was killed in the road and his silk was robbed. A retired policeman was in charge of the investigation. After two days, the investigator saw a boat on which there were many flies clustered on the washed silk. The police then arrested the men on the boat. The silk still had traces of blood.

Early Cases from Europe

•During mass exhumations in France and Germany in the 18th and 19th centuries medico-legal doctors (mostly Reinhard) observed that buried bodies are inhabited by many kinds of arthropods

-Phorid flies AKA coffin flies

•Orfila: Father of Modern Toxicology

•Among first to systematically record bodily decay in great detail

•Listed 30 insects/arthropods that visited a corpse

Early Cases from Europe p2

•1855: first modern forensic entomology case report to include an estimation of the postmortem interval (PMI)

•Bergeret d'Arbois - French doctor with an interest in cadaver study

•Case of mummified body of infant discovered in the bricked-up space behind the fireplace (1850)

Forensic Entomology in N. America

•1948: David Hall "The Blowflies of North America"- groundbreaking work in identification of blow flies

•Became curator of Diptera at National Museum

•Approached by FBI agents for casework

Forensic Entomology in N. America P2

•Curtis Sabrosky: successor of Hall; heightened awareness of importance of insects at crime scenes

•1961: Maggots in corpses: a measure of time of death

•Memorandum to FBI chief J. Edgar Hoover on usefulness of insect evidence

•Never acknowledged publicly

-I love him though

Forensic Entomology in N. America p3

1966: Sabrosky became first N. American Entomologist to take stand as a material witness

Case: Rural southwest Virginia: Charred remains of a young woman were discovered in a burned car at the bottom of a cliff. On autopsy, woman was found to have died of a gunshot wound to the head

•Evidence for the Entomologist:

-Exhibit A: a single puparium, found inside barrel of gun

-Exhibit B: Many more puparia found on floor mat of burned car

•Police already had a confession from the boyfriend but doubted the veracity of his claims that the crime was in a fit of passion (2nd degree vs. 1st degree murder)

•Gun and car found 50 ft apart

•Boyfriend claimed that in his distraught state he stumbled away from car, oblivious to where it had gone over the cliff

•Police suspected he returned later to conceal the crime deliberately burning body beyond recognition

Forensic Entomology in N. America p4

•By the 1960's, N. America had taken lead in making great strides in forensic sciences

-Largely due to Canada and US receiving copies of Mégnin's work

•However, "forensic" and "entomology" remained disconnected as ever

•Between the mid-1960's and early '80's, three Americans credited with creating a bona fide field of study

Forensic Entomology in N. America p5

•Jerry Payne: Ecological studies using carrion as model

•Painstakingly detailed research on the stages of decomposition and the insects that inhabit it

•Published in 1965 in Ecology

•C. Lamar Meek: LSU mosquito researcher with a focus on forensic entomology

•Published over 20 papers and book chapter about necrophilous arthropods in relation to investigations of homicides and deaths of high-profile wildlife

•Testified in more than 10 criminal trials, including the case upon which the film "Dead Man Walking" was based

•William Bass: renowned for his research on human osteology and human decomposition and research related to estimating the time since death (PMI)

•Founded the Forensic Anthropology Research Facility at the University of Tennessee ("the Body Farm")

Applications of "Forensic Science" Beyond Death Investigation

•The rationalist approach: science and law

•Broadly applicable to various fields

•Ability to observe evidence and make logical conclusions

•Appreciation for natural science

Taxonomic organization (KPCOFGS - what does each letter stand for).

•Kingdom

•Phylum

•Class

•Order

•Family (-idae or -ceae)

•Genus (always capitalized, in italics)

•Species (never capitalized, always in italics)

Insect Morphology: Body Plans

•Three body segments (tagma):

○Head

○Thorax

○Abdomen

Insect Head

•Ingest food

•Sense the exterior world

•House nerve center (brain); coordinate activities

Thorax

•Site of most locomotion

•Attachment for legs and wings.

•Three segments: PRO, MESO and META-thorax

•One pair of legs/ segment

•Wings on meso or meta

•Internal structure: muscle attachment, some organs (heart, glands, digestive tract)

Abdomen

•Usually quite non-descript

•Usually 7-10 segments

•Site of digestions, reproduction, waste management, respiration (along with thorax)

Insect Cuticle

•Protects against environment

•Seals in moisture with wax layer

•Made of a polysaccharide (a carbohydrate, chitin)

•Must be shed for growth

•Covers outside and parts of the digestive tract and trachea (breathing tubes)

Epicuticle: The thin outer layer of cuticle

Exocuticle: Outer, melanized (darkened) and sclerotized (hardened) portion of cuticle

Endocuticle: Soft, transparent, flexible portion of cuticle

Epidermis: The ectodermal cell layer of the integument which is one cell thick and secretes the cuticle

Trichogen cell: Epidermal cell that generates a seta (sclerotized hair-like projection)

Dermal gland: Unicellular epidermal glands which secrete wax, setae, pheromones, silk, etc.

Before Ingestion:

Maceration

Mandibles and other mouth parts

may tear up, or macerate, food.

• Often saliva is being added to the

food, starting digestions

Most insects have saliva

• It can do wonderful things!

• Digest other insect when injected!

• Numb your skin and keep your blood flowing!

• Breakdown starches in plants!

• May not be enough, so some insects (esp. flies) have

to vomit/regurgitate to break down food. Gross.

Foregut

Foregut

• Derived from ectodermal tissue and

lined by cuticle

• Shed in molting along with

exoskeleton

• Differentiated into:

• Pharynx: Ingestion and

passage of food

• Esophagus: Tube that

connects pharynx to crop

• Crop: Food storage

• Proventriculus: Maceration

and digestion

• Stomodeal valve: regulates

flow of food into midgut

Diverticulum

Crop is present in the foregut of all

insects, but it is sometimes modified

• Flies - general food storage

• Bees - nectar storage

• Ants & Termites - trophallaxis

• Communication using digestive fluids

• Diverticulum is present in all flies

• Separated midgut and crop, rather than

being linear

• Functions as food storage

Midgut

Elongate tube; primary

site of

digestion/absorption

• NOT lined by cuticle

• NOT shed during

molting

• In some insects, food in

midgut is partitioned

into peritrophic

membrane

Peritrophic membrane:

Membrane secreted by

cells lining midgut

• NOT shed during

growth

• Protects gut from

abrasion,

microorganisms,

toxins, etc.

• Packages waste for

excretion

• Frass

• Beetle frass can be used

in forensic entomology

Hindgut

Derived from ectodermal tissue and

lined by cuticle

• Shed in molting along with

exoskeleton

• Differentiated into:

• Intestine (anterior)

• Rectum (posterior)

• Malpighian tubules used to

regulate water and ion balance,

and remove waste from the

hemolymph

Neurological/Hormonal systems

Insect react to stimuli through a

nerve system

∙Modulated by hormones,

secreted by glands in head

• Molting hormone, juvenile

hormone

∙Various sensory inputs: eyes,

sensilla on antennae, feet,

mouthparts, genitalia, hairs

(setae) on body

Nervous System

Brain is the central part—three major lobes for

eyes, antennae, mouth/gut

∙ Large ganglia (nerve bundles): subesophageal

ganglion and dorsal (segmental) ganglia going

the length of the insect

• Help coordinate movement

∙ Fun note: many insects can live weeks without a

head...Yikes!

Sensory inputs

Visual (motion, shape, color)

∙ Chemical or chemoreception

∙ Mechanical

∙ Temperature/humidity

∙ Sound/hearing

Visual Inputs: Eyes

Compound eyes

• Most adult insects have these

• Made up of units called ommatidia

• Each ommatidia takes in light that changes a

pigment—together the insect can form an

image—many can see color, UV

• Very sensitive to movement (about 5x human

flicker-fusion frequency)

∙ Ocelli (simple eyes)

• A single lens eye for light/dark determination

• Short term - predators

Long term - seasonal change

Chemical or

chemoreception

Chemical or

chemoreception

∙Taste (aka gustation, mouthparts)

∙Tactile (tasting with feet using

chemonsensilla)

∙Olfaction (aka smell, mostly

antennae)

Mechanoreceptors

AKA Proprioreceptors

∙ Can be setae (hairs) to sense wind, "stretch"

receptors for limb flexing/touching, specialized

organs (feathery antennae/tympani as ears)

• Ormiini flies and prothoracic "ears"

∙ Physical bending sends neuronal signal

∙ Similar reception in trachea may signal molting

(more later)

Mechanoreceptors in skin Hearing

Not all insects can hear

• Most flies don't hear very much

∙ Many can and use sound to avoid predators ,

attract/detect mates , find prey

∙ Various adaptations to detect frequencies in

the air:

• Tympani

• Antennae

Mechanoreceptors temperature and humidity

Specialized receptors called

thermohygrometers seem to detect

temperature and humidity

∙These are critical for insects as they are

poikilotherms ("cold blooded")

Mechanoreceptors other senses

Monarch butterfly antennae contain cells

that can tell time and direction by the angle

of the sun.

∙ Many insects use polarized light detection

to tell direction.

∙ Ants can determine distance by counting

their steps.

Hemolymph

Open circulatory system

• Insect "blood", includes cells, signal

molecules, water, nutrients, etc.

• Functions in transport of nutrients,

hormones, wastes, etc.

• Osmoregulation is the balance of

salts and water in body

Insect Circulation

"Open" with main "blood" vessel located dorsal to

the digestive tract and extends from the abdomen to

the head

• Aside from dorsal blood vessel, hemolymph flows

unrestricted through body cavity

• Minor role in transport of O 2 and CO

Dorsal Vessel

Aorta: Anterior, nonchambered part of

dorsal vessel which transports

hemolymph to the head

• Heart: Pumping part of dorsal vessel in

abdomen possessing ostia

• Ostia (ostium): Perforations in dorsal

vessel which take in hemolymph from

the posterior of the insect

Tracheal System

An "open" system where oxygen

diffuses through larger trachae to finer

tracheoles

•Oxygen is taken from the outside

(atmosphere or water) through spiracles

Spiracles

May be on thorax or abdomen

• Found in adults and immatures

• The color of the hairs in spiracles can be important

in identifying adult forensic flies

• Important also in determining "age" of maggot and

sometimes family, genus, species

• The "back" spiracles, called anterior spiracles, have

straight slits and are not in a cavity in all blow fly

larvae

• Top right IS a blow fly larva!

Insect Growth and

Development

All insect life cycles begin with an egg stage

and end with an adult insect

· The path to get from egg to adult is what

varies, depending on the degree of

metamorphosis

Metamorphosis

a biological process by which an animal

physically develops after birth or hatching, involving a

conspicuous and relatively abrupt change in the animal's

form or structure through cell growth and differentiation

· Advantages:

Allows growth

Allows specialization between stages

Types of Metamorphosis

Ametabolous = no

change

Hemimetabolous

= incomplete

metamorphosis =

without a pupa

Holometabolous =

complete

metamorphosis =

with a pupa

Ametabolous

Ametabolous · No metamorphosis

· Only obvious difference

between nymphs and adults is

size

· Wingless adults

· With one exception: they get

genitalia

· VERY variable numbers of

instars; can sometimes even

molt as adults

· E.g. Silverfish; primitive

hexapods

· (also many arachnids)

Hemimetabolous

Wings develop externally from "pads"

· Nymphs (if present in adult) have compound eyes

· Nymphs and adults live in same habitat and feed on

same food

· Major structural difference: wings and genitalia

· Includes some important pests (potato leafhoppers,

locusts, aphids, scales, whiteflies)

· Most insect

orders are hemimetabolous

· Eg. True bugs, grasshoppers

Holometabolous

Complete metamorphosis

· Pupal stage: where the most dramatic

metamorphosis takes place

· Wings develop internally

· Larvae often wormlike

· Larvae never have compound eyes

· Larvae are typically long lived and do the most

feeding

· Adults are generally short-lived mate and

disperse

· Eg. Flies, beetles

Adults and larvae often feed

on different foods (exceptions:

predators)

· MOST insect

species are

holometabolous including

most insects of forensic

importance

Life Stages of Insects:

Immatures

Nymphs/naiads (incomplete)

· Larva/larvae (complete)

· Almost never* have wings or

genitalia

· Instar: A developmental stage of

arthropods between each molt,

until sexual maturity is reached

The number of instars varies

depending on the insect (~3-15)

May change in response to

environment

Blow flies have 3 larval instars

Instars

Most insect life cycles look like this :

Egg » » (Nymph 1 » » Nymph 2 » » Nymph 3 » » Nymph 4) » » Adult

or

Egg » » (Larva 1 » » Larva 2 » » Larva 3) » » Pupa » » Adult

(molts)

Life Stagesof Insects-

Pupa

Final immature stage directly preceding adult stage

· Usually immobile and non-feeding (and vulnerable!)

· Insect undergoes dramatic morphological change, gaining

compound eyes, wings, and usually entirely new body shape

Life Stages of Insects-

Adults

Recognized by wings in most cases, and

genitalia in all cases

· Compound eyes

· Paedogensis: when an adult looks like an

immature, also "larviform" adults.

Found in some fireflies and related beetles

Molting Hormones

Ecdysone

Released by prothoracic gland; triggers

molting and maturation

• Juvenile Hormone

(JH): Released by corpora allata gland;

keeps larvae from pupating during larval molts

Molting Process

Molting Process · Apolysis: physical

separation of old

exoskeleton from

epidermis

· Secretion of inactive

molting fluid by epidermis

· Production of new

cuticulin layer for new

exoskeleton (protects

epidermal layer from

digestion)

· Activation of molting

fluid

molting process p2

Molting Process

· Chemical digestion and

absorption of old

endocuticle by molting

fluid

· Epidermis (living layer)

secretes new procuticle

· Ecdysis- shedding of old

exo- and epicuticle;

includes external & linings

of tracheae, foregut, &

hindgut; not midgut

Expansion of new

integument

· Tanning & sclerotization

of new exocuticle-

darkening and hardening

Molting

Molting is the process whereby an

insect replaces its old exoskeleton,

allowing for growth

· Production of a new cuticle

(=exoskeleton) and the subsequent

shedding of the old cuticle

· It is triggered by hormones that are

released when the insect reaches its

size limit for the current exoskeleton

· The new exoskeleton is produced

inside the old one and then hardens

after shedding

Insect behavior

Response to stimuli

· Goes from canalized to plastic

· What kind of organisms

behave?

Canalized

In born, "instinctual"

· Little variation between individuals

· Evolutionarily fixed behavior

Plastic

Learned/changeable through experience

· Can see variation between individuals

both genetic and environmental

· Evolutionarily flexbile

Fresh Stage

Body temperature equilibrates to that of the

surrounding environment

• Autolysis begins

• Microbes in the digestive tract start to

break down the body

• These anaerobic bacteria give off many

gases

• Gases seep out of natural body

openings, attracting MANY flies

• Flies lay eggs around any openings/junctions

Bloat

Bloat

• Coagulation of blood seals the body

• Decomposers (mostly bacteria from the body)

consume nutrients and produce large amounts

of gas (CO2, others)

• Deoxygenation of coagulated blood causes

marbling—bluish outline. Internal pressure

can force blood out of bodily orifices, called

purging

• Insect activity increases; eggs hatch

Active Decay

Strong odor of decay

• Body deflates

• Fats begin to decompose

(saponify/saponification)

• Skin begins to turn black

• Fly larvae penetrate skin around

natural openings or wounds

• Beetles present, consuming fly larvae

• Carrion beetles

• Rove beetles

Advanced

Decay

Odor lessening—and changing

• Three types of fermentation take place

during this phase:

• Butyric - results in the smell of rancid

butter

• Caseic - results in the smell of rancid

cheese

• Ammoniacal - results in the production

of ammonia

• Very large #s of maggots and their predators

—maggots start migrating away to pupate—

other species of flies and beetles show up to

get at the hard-bits

Skeletonization

and beyond

Carcass reduced to dry skin, hair, cartilage

and other connective tissues, and bone

• Few fly species present

• Adult and larval beetles consuming remains

• Carpet beetles

• Checkered beetles

• Bones are hard to consume—few

organisms are capable of this (but some in

the ocean!)