Review for External Anatomy of the Insect Head 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 View Sclerotized regions Sclerite names Sutures Condyles antennal socket (2) ocellus (3) compound eye (2) gena vertex occiput frons subgena postocciput frontal suture subgenal suture postoccipital suture prothorax antennifer (antennal condyle) mandibular condyle (2) posterior tentorial pit (2) anterior tentorial pit (2) labrum clypeus mandible (2) maxilla (2) labium hypopharynx Review Topics

Generalized Head: Frontal View 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! gena vertex frons subgena labrum clypeus mandible frontal suture subgenal suture fronto-clypeal suture (epistomal suture) Review Topics

Insect Head - Oblique View partial dissection to show tentorium Not shown for clarity: Internal tissues: Muscle, nervous, digestive External: conjunctivae posterior tentorial pit anterior tentorial pit tentorial bridge anterior tentorial arm occipital foramen clypeus labrum frons mandible compound eye postocciput gena antennae dorsal tentorial arm Tentorial structures are sclerotized Internal strength to the head Additional attachment for various muscles 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 striking the corneal lens and crystalline cone is deflected to the rhabdom Light-gathering apparatus corneal lens The light signal is converted into nervous impulses by retinula cells crystalline cone corneagen cell (2) (primary pigment cell) Light-sensing apparatus Pigment can be concentrated within the pigment cells to allow more light entry under low light conditions rhabdom retinula cell (~8) secondary pigment cell (12-18) Review Topics

Many Ommatidia are Grouped to Form the Compound Eye Close-packed arrangement of the ommatidia Evidenced 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 Compound eye of Pterophylla camellifolia Review Topics

Other Photoreceptors Ocellus structure Single cuticular lens No crystalline cone Multiple rhabdoms and sense cells Ocellar nerve innervates deutocerebrum Stemma structure Single lens Crystalline lens usually present Multiple rhabdoms Stemmata arranged in image-forming clusters corneal lens ocellar nerve rhabdom retinula cell nucleus corneagen cell nucleus cuticle pigment corneagen cell nucleus corneal lens proximal rhabdom distal rhabdom crystalline lens sense cells Review Topics

Structure of the Antenna Generally 3 parts: Scape: basal most segment Pedicel: contains chordotonal organ Sense vibrations (sound in ♂ mosquitoes) Flagellum: 1-30+ segments Sensilla of several types present A given sensilla type usually concentrated in a particular region of the antenna Sensilla counts range from <8K to >250K flagellum pedicel scape Head capsule Review Topics

Movement of the Antenna 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 flagellum pedicel scape Head capsule antennifer (single condyle: ball-and-socket type movement) Review Topics

Generalized Insect Mouthparts Labrum Unpaired, articulates with clypeus by narrow membrane Allows considerable movement Forms “upper lip” Mandibles Paired, highly modified and sclerotized appendages capable of grinding food before ingestion Axis of rotation midline Mandibular adductors attach to this apodeme Mandibular abductors attach to this apodeme clypeus labrum Two mandibular condyles confine the movement of the mandible to a single axis of rotation mesad distad grinding region incising region Review Topics

Generalized Insect Mouthparts (cont.) Maxillae Paired appendages with several distinct sclerites, capable of further manipulating food Labium Unpaired, moderately modified One can envision two maxillae fused along the midline Acts as “lower lip” Two labial condyles confine the movement of the labium along a single axis of rotation midline Single condyle: movement not confined to single axis submentum mentum paraglossum glossae prementum palp cardo stipes lacinia galea palp mesad distad ligula

Generalized Mouthparts Ventral View Cibarium Anterior Mouth Labrum Mandible Maxilla Hypopharynx Labium Posterior Salivary gland opening Review Topics Salivarium

Not Generalized Pterophylla camellifolia (true katydid) Frons Gena Maxillary palp Mandible Labrum Galea of Maxilla Labial palp Review Topics

Review Topics