Wing venation, modifications and wing coupling apparatus
Wing venation and Modifications
Wing venation
Among the invertebrate animals, only insects possess wings. Wings are present only in adult stage. Number of wings varies from two pairs to none. Certain primitive insects like silver fish and spring tail have no wings (apterous). Ecto parasites like head louse, poultry louse and flea are secondarily wingless. Wings are deciduous in ants and termites. There is only one pair of wings in the true flies. Normally two pairs of wings are present in insects and they are borne on pterothoracic segments viz., mesothorax and metathorax. Wings are moved by thoracic flight muscles attached to their bases.
Wing is flattened double layered expansion of body wall with a dorsal and ventral lamina having the same structure as the integument. Both dorsal and ventral laminae grow, meet and fuse except along certain lines. Thus a series of tracheae, nerves and blood. Wing is nourished by blood circulating through veins. Later the walls of these channels become thickened to form veins or nervures. The arrangement of veins on the iwngs is called venation which is extensively used in insect classification. The principal longitudinal veins arranged in order form the anterior margin are costa (C) , sub costa ( Sc), radius ®, median (M), cubitus (Cu) and anal veins (A). Small veins often found inter connecting the longitudinal veins are called cross veins. Due to the presence of longitudinal veins and cross veins, the wing surface gets divided into a number of enclosed spaces rermed cells. In insects like dragon fly and damselfly, there is an opaque spot near the coastal margin of the wing called pterostigma.
Examples: Bugs (order Hemiptera).
1. Hamulate: A row of small hooks is present on the costal margin of the hindwing which is known as hamuli. These engage the folded posterior edge of fore wing. Eg: Bees.
Wing is flattened double layered expansion of body wall with a dorsal and ventral lamina having the same structure as the integument. Both dorsal and ventral laminae grow, meet and fuse except along certain lines. Thus a series of tracheae, nerves and blood. Wing is nourished by blood circulating through veins. Later the walls of these channels become thickened to form veins or nervures. The arrangement of veins on the iwngs is called venation which is extensively used in insect classification. The principal longitudinal veins arranged in order form the anterior margin are costa (C) , sub costa ( Sc), radius ®, median (M), cubitus (Cu) and anal veins (A). Small veins often found inter connecting the longitudinal veins are called cross veins. Due to the presence of longitudinal veins and cross veins, the wing surface gets divided into a number of enclosed spaces rermed cells. In insects like dragon fly and damselfly, there is an opaque spot near the coastal margin of the wing called pterostigma.
Margins and Angles
The wing is triangular in shape and has therefore three sides and three angles. The anterior margin strengthened by the costa is called costal margin and the lateral margin is called apical margin and the posterior margin is called anal margin. The angle by which the wing is attached to the thorax is called humeral angle. The angle between the costal and apical margins is called apical angle. The angle between apical and anal margins is called anal angle.
Wing Regions
The anterior area of the wing supported by veins is usually called remigium. The flexible posterior area is termed vannus. The two regions are separated by vannal fold. The proximal part of vannus is called jugum, when well developed is separated by a jugal fold. The area containing wing articulation sclerities, pteralia is called axilla.
Insects have evolved many variations of the wings, and an individual insect may posess more than one type of wing. Wing venation is a commonly used taxonomic character, especially at the family and species level.
In most living insects (the Neoptera), there are three axillary sclerites that articulate with various parts of the wing. In the Neoptera, a muscle on the third axillary causes it to pivot about the posterior notal wing process and thereby to fold the wing over the back of the insect. (In some groups of Neoptera, such as butterflies, the ability to fold the wings over the back has been lost.) Two orders of winged insects, the Ephemeroptera and Odonata, have not evolved this wing-flexing mechanism, and their axillary sclerites are arranged in a pattern different from that of the Neoptera; these two orders (together with a number of extinct orders) form the Paleoptera
Insects have evolved many variations of the wings, and an individual insect may posess more than one type of wing. Wing venation is a commonly used taxonomic character, especially at the family and species level.
In most living insects (the Neoptera), there are three axillary sclerites that articulate with various parts of the wing. In the Neoptera, a muscle on the third axillary causes it to pivot about the posterior notal wing process and thereby to fold the wing over the back of the insect. (In some groups of Neoptera, such as butterflies, the ability to fold the wings over the back has been lost.) Two orders of winged insects, the Ephemeroptera and Odonata, have not evolved this wing-flexing mechanism, and their axillary sclerites are arranged in a pattern different from that of the Neoptera; these two orders (together with a number of extinct orders) form the Paleoptera
Modifications of Wing venation
1. Tegmina
Tegmina (singular tegmen) are the leathery forewings of insects in the orders Orthoptera, Blattaria, and Mantodea. Like the elytra on beetles and the hemelytra on bugs, the tegmina help protect the delicate hind wings. Examples: Grasshoppers, crickets and katydids (order Orthoptera), Cockroaches (order Blattaria), Mantids (order Mantodea).2. Elytra
Elytra (singular elytron) are the hardened, heavily sclerotized forewings of beetles and are modified to protect the hind wings when at rest. Examples: All beetles (order Coleoptera).
3. Hemelytra
A variation of the elytra is the hemelytra. The forewings of Hemipterans are said to be hemelytrous because they are hardened throughout the proximal two-thirds, while the distal portion is membranous. Unlike elytra, hemelytra function primarily as flight wings.Examples: Bugs (order Hemiptera).
4. Halters
Halters are an extreme modification among the order Diptera (true flies), in which the hind wings are reduced to mere nubs used for balance and direction during flight. Examples: All flies (order Diptera).5. HAMULI
6. FRENULUM
7. MEMBRANOUS WINGS
Membranous wings are thin and more or less transparent, but some are darkened. Examples: Dragonfiles and damselflies (order Odonata), lacewings (order Neuroptera), flies (order Diptera), bees and wasps (order Hymenoptera), termites (order Isoptera). Note the paleopterous wing conditions of the damselflies and dragonfly to the right and below and the neopterous wing conditions of the other insects.8. SCALES
Some insect wings are covered with scales. The scales make the wings colorful. Examples: Butterflies, moths and skippers (order Lepidoptera), caddisflies (order Trichoptera).WING COUPLING
Higher pterygotus have attained virtual dipterist by coordinate wing movements. Such insects have devices for hooking fore and hind wings together so both the pairs move synchronously. By coupling the wings the insects become functionally two winged.TYPES OF WING COUPLING
1. Hamulate: A row of small hooks is present on the costal margin of the hindwing which is known as hamuli. These engage the folded posterior edge of fore wing. Eg: Bees.
2.Amplexiform: It is the simplest form of wing coupling. A linking structure is absent. Coupling is achieved by broad overlapping of adjacent margins. Eg: Butterflies.
3. Frenate: There are two sub types. Eg: Fruit sucking moth.
i. Male frenate: Hindwing bears near the base of the costal margin a stout bristle called frenulum which is normally held by a curved process, retinaculum arising from the subcostal vein found on the under surface of the forewing.
ii. Female frenate: Hindwing bears near the base of the costal margin a group of stout bristle (frenulum) which lies beneath extended forewing and engages there in a retinaculum formed by a patch of hairs near cubitus.
i. Male frenate: Hindwing bears near the base of the costal margin a stout bristle called frenulum which is normally held by a curved process, retinaculum arising from the subcostal vein found on the under surface of the forewing.
ii. Female frenate: Hindwing bears near the base of the costal margin a group of stout bristle (frenulum) which lies beneath extended forewing and engages there in a retinaculum formed by a patch of hairs near cubitus.
Frenate coupling - female -L Frenate coupling - male -R
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Entomology