Insect head

Entomology

1. Entomology 353 Bio T. Amani Alsharidah 1441 – 2019

2. lecture 4 The Insect Head

3. The Head The rigid cranial capsule has two openings, one posteriorly through the prothorax, the other to the mouthparts. Typically the mouthparts are: Hypognathous: The long axis of the head is vertical, and mouthparts are ventral. Such as Grasshoppers Prognathous: The long axis of the head is horizontal, mouthparts are anterior, such as Soldiers of termites Opisthognathous : The head is deflexed backwards so that mouthparts / proboscis slopes backwards between the front legs such as Homoptera and Hemiptera.

4. The Head In adult and nymphal insects, paired compound eyes between the vertex and genae , with a pair of sensory antennae placed more medially. In many insect three light-sensitive “simple” eyes , or ocelli , are situated on the anterior vertex, typically arranged in a triangle. The segmental origin of the head is most clearly demonstrated by the mouthparts. From anterior to posterior, there are six fused head segments : preantennal (or ocular); antennal; labral; mandibular; maxillary; labial. The neck is mainly derived from the first part of the thorax and is not a segment.

5. Lateral view of the head

6. The Mouth parts The mouthparts are formed from appendages of head segments . In omnivorous insects, such as cockroaches, crickets, and earwigs, the mouthparts are of a biting and chewing type (mandibulate) and resemble the probable basic design of ancestral pterygote insects more closely than the mouthparts of the majority of modern insects. Extreme modifications of basic mouth part structure, correlated with feeding specializations , occur in most Lepidoptera, Diptera , Hymenoptera, Hemiptera.

7. Type of mouth parts

8. 1- Basic mandibulate (Chewing) mouthparts There are five basic components of the mouthparts: labrum, or “upper lip”, with a ventral surface called the epipharynx Hypopharynx, a tongue-like structure. Mandibles, or jaws. Maxillae (singular: maxilla). Labium, or “lower lip”. The main function Biting off, chewing and swallowing small bits from plant and animal tissues. mandibulate mouthparts

9. 2- Chewing and lapping Mouth Part The mouthparts of bees are of a chewing and lapping-sucking type. Lapping is a mode of feeding in which liquid or semi liquid food adhering to the tongue is transferred from substrate to mouth. In the honeybee, Apis mellifera (Hymenoptera: Apidae). The elongate and fused labial glossae form a hairy tongue, which is surrounded by the maxillary galeae and the labial palps to form a tubular proboscis containing a food canal. The function of this mouth parts is collected nectar and honey. Frontal view of the head of a worker honey bee, Apis mellifera (Hymenoptera: Apidae)

10. 3-Siphoning Mouth Parts Most adult Lepidoptera and some adult flies obtain their food solely by sucking up liquids using suctorial (haustellate) mouthparts that form a proboscis or rostrum. The proboscis of moths and butterflies, formed from the greatly elongated maxillary galeae , is extended by increases in hemolymph (“blood”) pressure.

11. 4- Sponging/lapping Mouth parts A few moths and many flies combine sucking with piercing or biting. For example, moths that pierce fruit and exceptionally suck blood (species of Noctuidae ) have spines and hooks at the tip of their proboscis which are rasped against the skins of either ungulate mammals or fruit.

12. 5-Pierecing-Sucking Mouth Parts All dipterans typically have a tubular sucking organ. The proboscis, comprising elongate mouthparts (usually including the labrum). A biting-and-sucking type of proboscis appears to be a primitive dipteran feature. Although biting functions have been lost and regained with modifications more than once, blood feeding is frequent, and leads to the importance of the Diptera as vectors of disease. Blood-feeding flies have a variety of skin-penetration and feeding mechanisms.

13. Antennae Antennae are mobile, segmented, paired appendages. They appear to be eight-segmented in nymphs and adults, but often there are numerous sub- divisions, sometimes called antennomeres. The entire antenna typically has three main divisions: Scape: generally is larger than the other segments and is the basal stalk. Pedicel: nearly always contains a sensory organ known as Johnston’s organ, which responds to movement of the distal part of the antenna relative to the pedicel. The flagellum: is often filamentous and multisegmented (with many flagellomeres),but may be reduced or variously modified. The antennae are reduced or almost absent in some larval insects.

14. Typical structure of Antenna

15. Antenna Numerous sensory organs, or sensilla), in the form of hairs, pegs, pits, or cones, occur on antennae and function as chemoreceptors, mechanoreceptors, thermoreceptors, and hygroreceptors. Antenna Function: To serve as secondary sexual characters in male Lepidoptera and male mosquito. To find it’s way. To detect the danger. To find the food. To find the opposite sex. To communicate with each other e.g. Ants. It bear olfactory organs ( smell) e.g. Housefly It bears chordotonal organs (sound hearing) e.g. Male Mosquito. To detect humidity To hold the opposite sex at the time of mating. To catch the prey e.g. Mantids.

16. Type of Antenna Filiform antennae: have a thread-like shape. Examples: Ground beetles (order Coleoptera), Grasshopper (order Orthoptera). Setaceous antennae: have a bristle-like shape. Examples: Dragonflies and damselflies (order Odonata) cockroach. Filiform antennae Setaceous antennae

17. Type of Antenna Capitate antennae: are abruptly clubbed at the end. Examples: Butterflies (order Lepidoptera). Painted beauty butterfly. Clavate antennae: are gradually clubbed at the end. Examples: Carrion beetles (order Coleoptera).

18. Type of Antenna Lamellate or clubbed antennae: End in nested plates. Examples: Scarab beetles (order Coleoptera). Rose chafer, Macrodactylus subspinosus Serrate antennae: H ave a saw-toothed shape. Examples: Click beetles (order Coleoptera).

19. Type of Antenna Pectinate antennae: Have a comb-like shape. Examples: Fire flies (order Coleoptera). Geniculate antennae: Are hinged or bent like an elbow. Order Hymenoptera: Bumble bee, Bombus sp. Order Hymenoptera: Carpenter ant, Camponotus sp .,Ant

20. Type of Antenna Bipectinate antennae: Have a feather-like shape. Examples: Moths (order Lepidoptera). Plumose antennae: Have a feather-like shape. Example Order Diptera Mosquito male Culex sp. Male mosquito, Female Mosquito. Bipectinate antennae

21. Type of Antenna Aristate antennae: Are pouch-like with a lateral bristle. Examples: House flies (order Diptera ). Arista Order Diptera : House fly, Musca domestica Stylate antennae: Are three segmented. Tip of the antennae bears long bristle is known as style. Aristate antennae Stylate antennae