Insect head & antenna

Structure and modification of Insect head and antenna

1. Structure and Modifications of Insect head and antenna Prepared by Dr. S. Sumaiya

2. Structure of insect head Head capsule is sclerotized and the head capsule excluding the appendages formed by the fusion of several sclerites is known as Cranium Sclerites of Head Vertex Frons Clypeus Gena occiput The surface of the head is divided into regions ( sclerites ) by a pattern of shallow grooves (sutures). 

3. Sutures of head Epicranial Epistomal / fronto clypeal Clypeo labral Post occipital

4. Posterior opening of the cranium through which aorta, foregut, ventral nerve cord and neck muscles passes is known as Occipital foramen. Endoskeleton of insect cuticle provides space for muscle attachment of muscles of antenna and mouthparts – Tentorium . Cephalic appendages : antenna, eyes, mouthparts Structure of insect head

5. Insect Heads 3 basic types Hypognathous Prognathous Opisthorhynchous

6. Hypognathous head ( Hypo = below; gnathous = jaw) This type is called orthopteroid type . The long axis of the head is vertical. It is at right angles to the long axis of the body. Mouth parts hang ventrally downwards from head capsule. eg . Grasshopper, cricket, molecricket , cockroach, preying mantis, caterpillars, and most phytophagous insects living in open habitats.

7. Prognathous head ( Pro = infront ; gnathous = jaw)   This type is also called coleopteroid type . The long axis of the head is horizontal. It is in line with the long axis of the body. Mouth parts are directed forward. eg . Ground beetle, soldier termite, and predators that actively hunt their prey (grub and adults of beetles and the grub of green lacewings).

8. Opisthognathous head ( Opistho = behind; gnathous = jaw)  This is also called hemipteroid type or opisthorhynchous type . Head is deflexed. Mouthparts are directed obliquely backwards ( ventro-posteriorly ) and held in between the forelegs. eg . Stink bug.

9. Types of Insect Antennae

10. Antenna One Pair on head Jointed Sensory (smell) Called “ feelers ” Filiform most common shape (segments = size) May be modified FILIFORM

11. Antennal suture Antennifer Pedicel Scape Flagellum Antennal socket Antennal sclerite Insect Antenna

12. Segments in antenna Scape : The basal segment is called scape . It is conspicuously larger than succeeding segments. It is provided with intrinsic muscles. Pedicel: The second antennal segment is called pedicel. A mass of sense cells called Johnston's organ is present in the pedicel, which is used as a ‘ chordotonal organ’ ( chord + tonal ) in some of the insects like mosquitoes. Pedicel is also provided with intrinsic muscles. Flagellum: The remaining annuli or flagellomeres are known as flagellum (plural - flagella) or clavola . Flagellomeres are not true segments because they lack intrinsic muscle. Surface of the flagellum is supplied with many sensory receptors that are innervated by the deutocerebrum of brain.

13. Setaceous antenna These are simplest type of antenna having bristle shape They are found in dragon fly

14. Capitate antenna Abruptly clubbed at the end. Example-butterfly

15. Clavate antenna Eg : Blister beetle

16. Filliform antenna They have thread like shape Example-ground beetles

17. Geniculate antenna

18. Moniliform antenna

19. Pectinate antenna ( Unipectinate – comb like)

20. Bipectinate (Double comb like)

21. Serrate antenna They are saw toothed shape Example-click beetles or longicorn beetles

22. Aristate Antenna

23. Plumose antenna Segements with long whorl of hairs Ex: Male mosquito

24. Pilose (Hairy) Antenna is less feathery with fewer hairs at the junction of flagellomere e.g. female Culex mosquito.

25. Lamellate (Plate-like) Antennal tip is expanded laterally on one side to form that plates

26. Flabellate (Fan like) very small, third and subsequent segments with side processes giving fan like arrangements. Ex: Cedar beetle, Strepsipterans

27. Stylate antenna Terminal segment bear a style like process (Flagellum forms a long un segmented terminal hair Ex: Horse fly