chapter 1 - the insect body

8/8/2019 Chapter 1 - The Insect Body

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Forensic Entomology IE

Courtney SeelkeChapter One:

The Insect Body


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Homology

In order to applyanatomical terms to thedifferent types of insects,one must determinehomology.

Homology is the

identification of anatomicalparts that have structuralsimilarity because of acommon evolutionaryorigin.

Serial Homology isapplied to the samestructures on different

segments of anindividual.

Example: Legs on eachsegment of an arthropod


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Anatomical Positions

Anterior: front or head

Posterior: hind end or tail

Dorsal: upper surface or back

Ventral: lower surface or belly Lateral: side or outer part

Median: middle or inner part

Proximal: nearest to body; base

Distal: farthest from body; tip

Longitudinal: parallel to length

Transverse: perpendicular to axis


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Exoskeleton

The external support system Made up ofsclerites and tough flexible

membranous joints.

Can have modified hairs orsetae thatfunction as sensory organs

Common types:

Simple

Plumose

Scales

Poison

Can have spines orapodemes.

Apophyses connect to the exoskeleton toprovide muscle attachments and functionas the endoskeleton.

Any line seen on the surface of the insect'sexoskeleton is a suture.


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The Evolution of Insect Bodies

Insects evolved fromthe segmentedworms, orAnnelida.

In 1935, Snodgrassproposed asequence of stepsleading to the insectsthat are instructivenow.


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Evolution Stages Stage one: the wormlike ancestor has a cylindrical

body, with a tubular intestine running nearly the fulllength.

Stage Two: Aquires a pair of eyes and antennae. Eachbody segments develops a pair of movableappendages.

Stage Three: Becomes an arthropod with jointed legsand enlarged sensory apparatus. Has becometerrestrial.

Stage Four: Body regions become specialized.

Final Stage: Only 3 body regions remain, each

specialized for a specific duty. Head sense organs, sensing enviroment,

ingesting food.

Thorax locomotion and houses large muscles

Abdomen reproductive organs and intestines,as well as airflow


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Primary Segments

Head

Thorax

Abdomen

There is a distinction made between primary segments,which correspond to true embryonic segments, andsecondary segments, which are functional subdivisions.


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Secondary Segmentation

When insectsevolvedexoskeletons, a

problem arose. Howwould the musclesmove the segments ifthe soft body wall

became sclerotized?

The evolutionary solution was:

1) Keep the musclesattached to trueintersegmental lines

2) Develop the rigidsclerites to include thetrue intersegmentallines so that thesclerites can bemoved by the muscles

3) Place lines of flexibilityjust in advance of thetrue intersegmentallines.


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Head

Contains the feedingappendages, importantsense organs and brain

Leads the way when theinsect moves forward

Detects changingphysical and chemical

properties Color, moisture,

touch, sounds,odors and flavors

Articulates with the bodyat the cervix

Contains a large hole in

which passes the Ventral nerve cord,

salivary ducts,foregut, aorta,

trachea,hemolymph andvarious muscles


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Head

Parts of the Head

Cranium

Antennae

Mouthparts

Three positions of the head

Hypognathous: mouthpartsdirected downward,immediately ventral to thehead capsule(grasshoppers)

Prognathous: mouthpartsare directed forward andproject anterior to the eyes(beetles)

Opisthognathous: thesucking beak is directedtoward the rear, beneaththe thorax (Homoptera)


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Head - Cranium

The sclerotized head capsule, minus theappendages.

Contains compound eyes

Internal structure called tentorium

Anteriorand Posterior tentorial pitsmark invaginations of the arms that meetmedially to form the tentorial bridge.

Three facial areas:

Vertex: summit of the head,between & behind eyes

Frons: between the antennae& eyes

Clypeus: area of craniumwhere the labrum isattached

Other parts of the cranium:

Labroclypeal suture

Frontoclypeal suture

Gena

Clypeogneal suture

Subgenal suture

Subgena

Occipital suture

Postoccipital suture

Occiput

Post occiput

Occipital condyles

Occipital suture

Postgena


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Modifications of the Cranium

The sutures andareas of the craniumcan vary quite a bit

due to placement ofmouth parts andmusculature.

Sometimes there arenew, distinctive areasto develop in certaingroups of insects.

Special terminology

Postclypeus: theprominent bulgebetween the eyes thathouses the musclesfor a sucking pump

Anteclypeus: smallerarea below thepostclypeus

Hypostomal or

postgenal:secondarily sclerotizedforms of Postclyperusand Anteclypeus


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Head - Antennae

Paired, segmentedappendages that attach tothe cranium around thearea of the compound

eyes. Three parts:

Scape

Pedicel Flagellum

Moved by muscles from thehead that insert on thescape.

Antenna may pivot on an

articular process orantennifer.

The Johnston's organdetects movements of the

flagellum


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Modifications of Antennae


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Head - Mouthparts

The mandibulate is the basictype from which specializedmouthparts are derived.

Contains:

Labrum: upper lip

Paired mandibles

Paired maxillae

Labium: lower lip

A median tonguelikehypopharynx

These enclose the true mouth, orpreoral cavity, and salivaryglands

The mandibles are heavilysclerotized jaws.

The inner edge is for biting andmay be hardened by deposits ofzinc, manganese, or iron.

The tip contains cutting teeth andthe base is a grinding surface.

The maxillae are the second pairof jaws, less massive andretaining the segmentation of anappendage.

These are muscled as to beindividually movable.


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Modifications of Mouthparts

Insect mouthparts vary in structure and functiondepending on what the insect eats.


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Thorax This second body

division is specializedfor locomotion.

Three segments: Prothorax:

forelegs

Mesothorax:

middle legs Metathorax: hind

legs

The Thoracic Notacontains the wing-bearing sclerite.

The Thoracic Sterna isventral and containsmany sutures.

The Thoracic Pleuraprovides support andpoints of attachment for

the legs and wings.


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Modifications of the Thorax

The pterothoracic segments are nearlyequal in size and structure in insectsthat have equal muscular power in both

parts of wings. Insects that fly with the wings coupled

tend to have an enlarged mesothorax toaccommodate the dominate fore wings.

In insects that fly with the hind wings,the metathorax is enlarged.


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Thorax - Legs

Six segmentsbeginning at base:

Coxa

Trochanter

Femur

Tibia

Tarsus Divided into 5

tarsomeres

Pretarsus

The pretarsus ismoveable bymuscles that

originate in the tibiaand femur.

In some insects thepretarsus is a par ofungues, ortarsalclaws, and aarolium.


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Modifications of Legs

Raptorial forelegs

Natatorial legs

Fossioral legs

Saltatorial hind legs

Cursorial Legs

Prehensile orCheliform legs


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Thorax - Wings

During development, thewings are saclike on thelateral body walls. Theupper and lower sacs

partially fuse and leave asystem of narrow, blood-filled channels. Trachea andnerves grow up thesechannels. At maturity mostof the channels aretransformed into wing veinsthat support themembranous portions.

The wing base house smallarticulatory sclerites. Theseinclude 3 axillary sclerites,the humeral plate, and the

median plate. The longitudinal wing veins

are: costa, subcosta,radius, media, cubitus,anal andjugal


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Modifications of Wings


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Abdomen

Last body divisioncontains the viscera,most of alimentary canaland dorsal circulatory

vessel and reproductiveorgans

On the 8th and 9thsegments on the female

and the 9th on the malesare the externalgenitalia

Contains the ovipostior(used for depositingeggs) in the female andthe aedeagus (a

median intromittentpenis) in the males.

Also contains a dorsalepiproct and lateral

paraprocts on theeleventh segment.


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Abdomen and External Genitalia


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Modifications of the Abdomen

Modifications of Cerci Modifications of ovipositors


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References

Introduction to Insect Biology and Diversity by

Daly, Doyen, and Purcell

Google Images


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chapter 1 - the insect body

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