Entomology 2002
Review for
External Anatomy of the Insect Head
Review Topics• Lateral view of the generalized head
• Frontal view of the generalized head
• Sclerotized structures inside the head
• Visual organs
• Antenna structure
• Mouthparts
• Ventral view of the mouthparts
Head Anatomy – Lateral ViewSclerotized regions Sclerite names Sutures Condyles
prot
hora
x
frontal
suture
subgenal suture
post
occi
pita
l sut
ure
labrum
clypeus
mandible (2) maxilla
(2)
labium
gena
vertex
occi
put
frons
subgena
post
occi
put
antennal socket (2)
ocellus (3)
compound eye (2)
posterior tentorial pit (2)
anterior tentorial pit (2)
hypopharynx
antennifer(antennal condyle)
mandibular condyle (2)
Review Topics
Generalized Head: Frontal View
Review Topics
gena
vertex
frons
subgena
labrum
clypeusmandible
frontal suture
subgenal suturefronto-clypeal suture (epistomal suture)
antennal socket (2)
compound eye (2)
ocellus (3)Don’t click yet!!! The
thing is alive!!Click after the ‘feelers’ are
gone and it doesn’t have any more feelings!
Insect Head - Oblique Viewpartial dissection to show tentorium
Not shown for clarity:Internal tissues: Muscle,
nervous, digestive
External: conjunctivae
Tentorial structures are sclerotized– Internal strength
to the head– Additional
attachment for various muscles
dorsal tentorial arm
clypeuslabrum
fronsm
andi
ble
compound eye
po
sto
ccip
ut
genaantennaeposterior tentorial pit
anterior tentorial pit
tentorial bridge
anterior tentorial arm
occipital foramen
Review Topics
Insect Photoreceptor Organs• Compound eyes
• Paired, symmetric• Composed of grouped
ommatidia • Between 1-30,000/eye
• Image-forming• Where visual fields
overlap the insect has depth-perception
• Variable capability to perceive different wavelengths• Apis cannot see red, but
can see UV
• Ocelli• Usually 3 (otherwise none
or two present)• On the frons or vertex of
many adults and nymphs• Single lens; not image-
forming• Stemmata
• In two groups on side of head capsule
• Found only in immature holometabolous insects
• Structurally intermediate between compound eyes and ocelli
• Image-forming when grouped
Review Topics
Structure of the Ommatidium• Light Light striking the corneal
lens and crystalline cone is deflected to the rhabdom
• The light signal is converted into nervous impulses by retinula cells
rhabdom
secondary pigment cell (12-18)
corneagen cell (2) (primary pigment cell)
crystalline cone
corneal lensLight-gathering apparatus
Light-sensing apparatusretinula cell (~8)
•Pigment can be concentrated within the pigment cells to allow more light entry under low light conditions
Review Topics
Many Ommatidia are Grouped to Form the Compound Eye
Close-packed arrangement of the ommatidiaEvidenced by the
hexagonal appearance of external surface of eye
Each ommatidium is angled slightly from neighbors to permit wide-angle views
Nervous inputs from all the ommatidia are integrated within the optic lobe and the protocerebrum
Review TopicsCompound eye of Pterophylla camellifolia
Ocellus structure• Single cuticular lens• No crystalline cone• Multiple rhabdoms and
sense cells• Ocellar nerve innervates
deutocerebrum
Other PhotoreceptorsStemma structure• Single lens• Crystalline lens usually
present• Multiple rhabdoms• Stemmata arranged in
image-forming clusterscorneal lens
ocellar nerve
rhabdom
retinula cell nucleus
corneagen cell nucleuscuticle
pigment
Review Topics
corneagen cell nucleus
corneal lens
proximal rhabdom
distal rhabdom
crystalline lens
sense cells
Structure of the AntennaGenerally 3 parts:
Scape: basal most segment
Pedicel: contains chordotonal organSense vibrations (sound in ♂ mosquitoes)
Flagellum: 1-30+ segments
Sensilla of several types presentA given sensilla type usually concentrated in a
particular region of the antenna
Sensilla counts range from <8K to >250Kflagellum
pedicel
scape
Review Topics
Head capsule
Movement of the Antenna
flagellum
pedicel
scape
Review Topics
antennifer(single condyle: ball-and-socket type movement)
Head capsule
Only the scape has any internal musculature Exception in Diplura, which has musculature
throughout
Contraction of muscles originating on head capsule inner wall and inserting on scape cause scape & more distal segments to move
Muscles originating in scape and inserting on pedicel move pedicel and flagellum
Monocondylic attachment means antenna rotates freely about point of articulation
Generalized Insect MouthpartsMandibles
• Paired, highly modified and sclerotized appendages capable of grinding food before ingestion
LabrumUnpaired, articulates with
clypeus by narrow membraneAllows considerable
movementForms “upper lip”
grinding region
incising region
Axis of
rotation
Mandibular adductors attach to this apodeme
Mandibular abductors attach to this apodeme
Two mandibular condyles confine the
movement of the mandible to a single
axis of rotation
mesad
distad
Review Topics
clypeus
labrum
midline
Generalized Insect Mouthparts (cont.)Labium
Unpaired, moderately modifiedOne can envision two maxillae
fused along the midlineActs as “lower lip”
submentum
mentum
paraglossum
glossae
prementum palp
ligula
midline
Maxillae• Paired appendages with
several distinct sclerites, capable of further manipulating food
mesad
distad
cardo
stipes
laciniagalea
palp
Single condyle: movement not
confined to single axis
Two labial condyles confine the movement of the labium along a single axis of rotation
Generalized MouthpartsVentral View
Labrum
Anterior
Posterior
Mandible
Maxilla
Labium
Hypopharynx
Mouth
Salivary gland
opening
Cibarium
SalivariumReview Topics
Not GeneralizedPterophylla camellifolia
(true katydid)
Review Topics
Frons
Gena
Maxillary palp
Mandible
Labrum
Galea of Maxilla
Labial palp