Insect body plan and integument

I. Integument as exoskeleton
II. Structure
A. Major Components
B. Composition
III. Insect body plan
IV. Introduction to Insect
Orders

Integument as exoskeleton – Complex structure of diverse function
• Nearly unlimited area for muscle attachment (and organ attachment)
• Protective – physical protective surface
• Protective – Biological (pathogens, virus, fungus etc)
• Water Retention
• Interface b/t insect sensory & exocrine structures and environment.

Integument as exoskeleton – Other functions
• Feeding – mouthparts, variations and strength
• Locomotion – wings, legs and prolegs
• Reproduction – external genitalia are exo modifications
• Many internal parts are also lined integument – tracheal system, fore &
hind gut and must be shed when molting

Epidermis - composed of 3 layers – From the inside out:
• Basement Membrane – Noncellular layer – 0.05 µm – micrometer
(1/1000)
• Epidermis – Cellular layer ‘alive’
• Cuticle – Noncellular layer – can be up to ½ dry weight (but varies)

Basement Membrane – Basal Lamina:
• Noncellular layer – 0.05 µm thick
• Composed of “amorphous granular material” most likely
Mucupolysaccharide
• Provides support for epidermal cells
• (-) charged and physical properties = effective sieve

Epidermis – cellular and biologically active part of integument
• Cellular layer responsible for secreting both basal lamina & cuticle
• Typically only one cell layer thick
• Most important tissue b/c it regulates molting, type of cuticle to lay
down, placement of specialized cells (sensory, scales etc)
• Interspersed w/in epidermis are dermal glands (associated w/ cuticle
production) with pore canals leading into cuticle

Cuticle – noncellular layer, complex
• Properties vary spatially, temporally contingent upon demands of
function and growth
• Chemical and physical properties of regions reflect locally specific
genetic expression of epidermis

Cuticle – can be divided into 4 basic regions (from inside out)
• Endocuticle – composed of growth layers (light and dark layers
corresponding to daily cycles
• Mesocuticle – only know it b/c it stains, function unknown
• Exocuticle – Highly stable, resistant to molting fluid – exuvia
• Epicuticle – very thin yet very complex

Cuticle – Epicuticle 0.03 um – 4 um thick, procuticle up to 200 um
• Endocuticle and Exocuticle together comprise the Procuticle
• Compared to hard areas of cuticle, softer regions typically comprised of
only endo- & epicuticle – referred to as arthrodial membrane
• Laid down lamellate at right angles (dark layers = day, light layers = night)

Epicuticle –
Cement layer
Superficial layer
Outer epicuticle
Inner epicuticle

Cement Layer
• Not present in all spp
• Produced by dermal glands
• Provides protection for layers below
• Similar to shellac

Superficial Layer
• Composed of two parts: oriented and
randomly oriented wax molecules
(monolayer)
• Critical for conserving water
• Lipids and hydrocarbons (recognition,
sex attractants, mounting stimulants
etc)
H 2 O
loss
Temp
+ Heat =

Outer Epicuticle
• 1 st layer to be secreted for new cuticle
• Covers all integument surface
including gut and tracheae

Inner Epicuticle
• Thought to be responsible for limiting
cuticle expansion b/t molts

Chemical composition of Cuticle
• Chitin – 25 – 50% dry weight – polysaccharide mostly
N-acetylglucosamine
• Proteins – Major constituent several kinds:
A – Sclerotins – involved w/ xlinking protein molecules and hardening
B – Arthropodins – soluble proteins
C – Resilin – stretchy, rubbery protein, stores energy, common around
wing hinges etc.

GENERAL INSECT BODY PLAN

GENERAL INSECT BODY PLAN
Tagma
Head = 3 segs pregnathal &
3 gnathal segs (mandibles, maxillae, labium)
Thorax = 3 segments each w/ 1pr of legs; each
true leg has 6 segments (extant, 11 ancestral)

Head

Thorax

Thorax

Abdomen

Epiclass: Hexapoda
United by:
•Fusion of 2 nd maxillae into labium
•Fixed # ab segs @ 11 – Ancestrally
•Tagmosis – head, thorax, ab
(body segs unite to form tagma)
What makes things baffling is their degree of
complexity, not their sheer size; a star is simpler than
an insect
- Martin Rees, 1999 (The Scientific American)

Entognatha
Primary Characters uniting this group:
•Mouthpart appendage recessed into gnathal pouch – this is a derived condition
(apomorphy) ancestrally arthropods are ectognathus.
•Mandibles monocondylic (articulated singly) – also only this group of hexapods that have
protrusible and retractable mandibles (Insects – only maxillae do that)
•External fertilization – possess gonopores for depositing and receiving spermatophore
• Molting occurs after adult stage is reached

Order: Protura - “first – tail”
Characters:
•Minute (~ 0.5 – 1.6mm)
•Head conical, scraping mouthparts
•No eyes or antennae
•1 st pair of legs – sensory
•12 abdominal segments (in adult)
•1 ab. seg. added each molt (9-11)
(anamorphic)
•Gonopore on Ab 11
•Rudimentary appendages
On 1st 3 Ab segs

Order: Protura
Biology
• ~ 500 species world wide
•Moss, rotting wood, soil, leaf litter etc.
•Thought to feed on mycorhizal fungus
•Biology poorly known
•Functionally “tetrapods”
•Virtually no fossils

Order: Collembola “glue-wedge”
Characters:
• Reduction of ab segs to 6 (appears fewer)
• Abdomen w/ sucker-like ventral tube – collophore (1)
retaining hook (3) and furcula (4), gonopore (5), anus (6)
• larval development epimorphic (no segs added)

Order: Collembola
Biology:
•9000 sp WW
•Most common ‘entognath’
• 3 – 6 mm
• Feed on decaying matter, fungus, bacteria, pollen, feces, etc
• Very numerous – up to 100k per m 3

Order: Diplura “two-tail”
Characters:
• Two caudal filiments
• eyes, ocelli absent
• antaenna long
• Styli present on ab segs (1/2 – 7)

Order: Diplura
Biology:
• 1000 sp WW
•< 7mm usually
• Dwell in soil
• Biology poorly known
• No fossils

Class: Insecta
United by:
• Typically ocelli/compound eyes
• Ectognathous w/ mouthparts well developed
• Thoracic legs w/ > 5 segs
• Ab ancestrally 11 segs w/ gonopore
female (8), male (9)
• Cerci present basally
• Gas exchange via trachea – many mods

Mandibles monocondylic
(articulated singly)
A - Insects

The Apterygote Insects
Order: Microcoryphia “small-head” – Jumping bristletails
Characters:
• Cylindrical body
• Compound eyes large and contiguous, ocelli always present
• 3 caudal filaments

Order: Microcoryphia
Biology:
• ~ 500 sp WW
•Many ecosystems
• Most nocturnal
• Active – can leap 25 cm!

Order: Thysanura “fringe-tail”
Characters:
• Compound eyes widely seperated
• ~ 500 sp WW
Habitat: feed on starchy products
• Can be a problem for books, bindings
with glue,
•Look in the bathroom

Infraclass – Pterygota
Paleoptera (informal grouping)
• Lack wing flexion mech to fold wing over ab
• Only extant orders of once diverse lineage

Order: Ephemeroptera “Short-lived”
Characters:
• 3100 sp WW
•Most basal extant lineage of winged insects.
• Mouthparts vestigial as adults and that phase lasts 1 day
• Aquatic larvae (not an ancestral condition)
• Feed chiefly on algae and detritus

Order: Odonata “tooth”
Characters:
• 5500 sp WW
•All nymphs are aquatic and predaceous
• Highly active flying hunters
• Many aquatic environments

Neoptera – new winged insects
Able to fold wings over ab

Order: Plecoptera “folded/plaited-wings”
Characters:
• 2000 sp WW
•Nymphs are aquatic
• Both adults and larvae feed on algae

Order: Blattodea and the subsuming of Isoptera?

Super Order: Dictyoptera
Orders: Mantodea, Blattaria, Isoptera (1800, 4000, 2900 sp WW)
Closely related but now it seems that Isoptera is a highly derived family of
Blattaria.

Order: Gryllobattodea
• 41 sp WW
•Discovered in 1914
• 15-30 mm
• 25 sp WW
• Live in extreme environments

Order: Mantophasmatodea
• 1 st described in 2001 from 30 my amber
• 20 - 30mm
• One family and 3 genera
• Predaceous
• S. Africa, now known for its endemism (~41 sp)

Order: Phasmatodea
• 3000 sp WW
•Slow moving herbivorous
• 2000 species WW
• Widely dist, but richest in the tropics

Order: Embiidina “lively”
• 500 sp WW
•Superficially resemble Plecoptera
•Produce silk from cellular glands on anterior basal tarsus
• Spend life in spun silken galleries in litter, soil, rocks, etc
• One introduced sp in NA is Parthenogenic
• Adult males do not eat

Order: Orthoptera “straight -wings”
• ~ 20,000 species
• Known for their enlarged hind legs – jumping
• Many produce sound via stridulation
• Early branch in polyneoptera
• Herbivore –Omn–Predatory

Order: Dermaptera “skin – wing”
• ~ 2,000 WW
• modified forewings, under which the
hind wings fold
• largely nocturnal, feed on detritus but
can be a pest

Order: Zoraptera “pure-wingless”
• 32 sp WW
• < 3mm
• principal food is fungal spores – we
think
• Can be found in ‘colonies’ under bark

Sub Division Paraneoptera – Hemipteroid assemblage

Order: Psocoptera “rub small”
• 4400 sp WW
• < 6mm
• Feed on spores, algae, molds, cereals
• Either gregarious or not
• Certain sp can vector fringed tapeworm
of sheep

Order: Phthiraptera “lice – w/o wings”
• 4900 sp WW
• Small wingless ectoparasites on birds and mammals
• Both chewing and sucking types, which are distinct

Order: Hemiptera
• 90,000 sp WW
• All life histories practiced
• Most diverse Hemimetabolous insects
• Sucking mouthparts
• Lumpers/splitters

Order: Thysanoptera “fringe”
• 5000 sp WW
• 0.5 – 5mm
• Many feed on living plant material, some predators
• Metamorphosis is somewhat intermediate b/t Hemi and Holo – metabolous
insect – 1 st 2 instars – no visible wing pads and other features
• Very Numerous

Sub Division Endopterygota – Holometabolous insects

Order: Neuroptera “nerve - wings”
• 6500 sp WW
• Most larvae predaceous, many are aquatic (not lacewings)
• Adults weak flyers
• Some (Rhaphidioptera) are parasitic in spider egg sacks

Order: Coleoptera “sheath - wings”
• 350,000 sp WW
• ALL habitats exploited

Order: Strepsiptera “twisted - wings”
• 550 sp WW
• Parasitic on other insects
• Males winged, Females highly modified
• The Enigmatic Order
• Life cycles very complex

Order: Diptera “two - wings”
• 120,000 sp WW
• Pervasive
• Most agile flyers
• Hind wings reduced to halteres (gyroscopes)
• Exploit any and all niches

Order: Mecoptera “long - wings”
• 600 sp WW
• 9 – 25 mm
• Pronounced ‘beak’
• Most generalized Holometabolous insect
• Complex mating rituals involving nuptial gifts

Order: Siphonoptera “tube - wingless”
• 2500 sp WW
• Small
• Compressed laterally
•Highly modified ectoparasites
• Adults depend on blood of warm blooded verts (w/ rare exception)
• Larval are free living feeding on organic matter
• Covered in stiff backward facing setae and spines

Order: Trichoptera “hair – wings”
• 11,000 sp WW
• Aquatic larvae live in various freshwater conditions
• Larvae construct cases out of material that is species specific

Order: Lepidoptera “scale - wingless”
• 150,000 sp WW
• Most recognizable and liked insect (at least butterflies)
• Larvae have large impacts on ecosystems (herbivory)

Order: Hymenoptera “god of marriage”
• 125,000 sp WW
• Ants, Bees, Wasps
• Also have large impacts of ecosystems.
Hmmm….. Let me count the ways