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INSECT ANTENNA Its origin, structure, function and modification in different orders of insect
- 1. INSECT ANTENNA Its origin, structure, function and modification in different orders of insect
- 2. Origin of Antenna It is mobile jointed appendages found in pair and articulated with head in front or between the eyes. The base of the antenna is set into a small membranous area of the head called the antennal socket. The rim of the socket is often strengthened by an internal submarginal ridge formed by an external inflection, the antennal suture. Usually a pivot like process on the rim of the antennal socket forms a special support and articular point for the base of the scape, allowing the antenna a free motion in all directions. The pivot or antennifer, is generally ventral but is not always so, and in some cases it is obsolete or absent.
- 3. Structure of Antenna Antenna is consists of three parts: 1. Scape: It is the first (basal) segment of antenna, which articulates with the head capsule through antennifer that provides movement for the scape. 2. Pedicel: It is the 2nd or middle segment of antenna that forms a joint between scape and flagellum. It consists of the special auditory organ known as “Jhonston’s organ”. Jhonston’s organ is absent in collembola & diplura. 3. Flagellum: It is the last antennal segment which consists of many segments that varies in shape and size. The remaining part of antenna and it varies greatly in forms of different families of insects. E.g. In chalcidoidea (geniculate antenna) the flagellum is divisible into ring like structure or ring structure as well as funicle or club like segments.
- 4. Function of Antenna The main function of antennae is sensory, which is modified according to use and need of insect as given below. 1. Organs of smell: In some insects the smell organs (sensoria) are situated in the antennae by which they recognize their food etc. Ants, honey bee and jaint moths. Smaller "sensilla" occur on various parts of the antennae. Most important are sensory hairs. Sensilla are often concentrated in particular regions. Functions of sensilla are tectile and smell receptors, contact receptors, hygroreceptors and temperate receptors. 2. Organs of taste: Some insects bear taste hair on their antennae by which they know the taste of their food e.g. Cockroach. 3. Stridulatorial organs: Sound producing organs are located in the antennae of some insects belonging to the orders coleopteran and orthoptera e.g. Crickets.
- 5. 4. Organs of chordotonal: The hearing organs often knows as johnston’s organ are situated in the second segment (pedicel) of antenna e.g. Male mosquito, green bottle fly and paper wasp etc. 5. Sexual characters (taxonomic importance): In some of the insects belonging to the order diptera and hemiptera, the antennae are found of different type in male and female e.g. Pilose antennae in certain female mosquito (Diptera), plumose antennae in male mosquito (Diptera). 6. Other functions: To find the foods. To find the ways. To warrant against danger. To find mate. To communicate with other members. In larvae of hymenoptera and diptera, the antennae are reduced to minute tubercles. In newly hatched larva of hydrophilus the antennae assist the mandibles in masticating the prey. In butterflies having some transmitting and receving organs in their antennae.
- 6. Modification of Insect Antennae 1. Filiform (Thread like) :- • Segments are more or less uniform and cylindrical in shape while size reduced towards distal ends. • E.g. Orthoptera (Grass hopper, crickets), Dictyoptera(mantids), Coleoptera (ground beetle, tiger beetle), Dermeptera (earwigs) 2. Moniliform (Bead like):- • All the segments are spherical (oval) in shape and uniform in thickness. • E.g. Isoptera(Termite worker), Coleoptera (rove beetle)
- 7. 3. Setaceous (Bristle like) :- • Segments are becoming slenderer from base to apex (pointed). • E.g. Dictyoptera (Cockroach), Odonata (dragonflies, damselflies), Hemiptera (aphids, whiteflies, hoppers) 4. Serrate (Teeth of saw like):- • Each segment is projected towards one direction and triangular in shape. • E.g. Coleoptera (Mango stem borer, pulse beetle)
- 8. 5. Clavate (Clubbed shaped):- • Segment gradually enlarges towards the distal end. Last few segments are round cone like. • E.g. Lepidoptera (Cabbage butterfly). Coleoptera (Khapra beetle, Leaf weevils etc.) 6. Capitate (Knob like): • Segment gradually enlarges towards the distal end and enlarged to form a knob like structure. • E.g. Lepidoptera (Lemon butterfly), Coleoptera (red flour beetle, blister beetles).
- 9. 7. Pectinate (Comb like): • The antennal segment have long processes on one side of antenna and it appears as a comb. • E.g. Lepidoptera (Sugarcane root borer), Coleoptera (firefly beetle, soldier beetle), Hymenoptera (Sawfly) 8.Bipectinate (Double comb like): • Segments have long processes on both the sides of antenna. • E.g. Lepidoptera (silk moth, sheep moth)
- 10. 9. Lamellate (Leaf like): • Terminal segments expand to one side into lateral oval lobes. • E.g. Coleoptera (Dung roller, Rhinoceros beetle) 10. Flabellate (fan-shaped): • The terminal segments extend laterally, with long, parallel lobes that lie flat against one another like the folds of a fan. • E.g. Male strepsiptera, Stylopids etc.
- 11. 11. Plumose (Feather like): • Between each segment, there is a bunch of hairs and makes feather like structure. • e.g. Male mosquito (Diptera) 12. Pilose: • Looks like plumose but each whorl contains less numbers of hairs. • E.g. Female Mosquito (Diptera)
- 12. 13. Aristate: • First segment is smaller and broader while the second is longer than first. The flagellum is longer than both and bears a bristle called arista on its dorsal side. • E.g. Diptera (House fly, syrphid fly) 14. Stylate: (Spine like) • Terminal segment elongate into long bristle called as stylate. • E.g. Diptera (Robber fly, snipe fly)
- 13. 15. Geniculate (Elbow like): • Typical antenna of the insect. • The antenna bent abruptly at the distal end of scape and the flagellum is at right angle to the scape. • e.g. Hymenoptera (Honey bee, Ants) Ant Honey bee