Insect wing venation and structure

3. The success of insect as terrestrial animals is at least partly due to
their ability of fly
The wings arise as outgrowth of the integument between the tergal
and the pleural sclerite, thus comprising tow layers of integument.
A series of tracheae grows between these two layers of integument
and becomes the longitudinal and transverse supportive framework
called the wing veins and the arrangement of veins is called the wing
venation
 The cuticle is often thicken in the region of these veins lending
further rigidity
 Since the wings are integumentary outgrowth the space between the
two (upper and lower) epidermal layers is continuous with the body
cavity or haemocoel

4. The space is seen only around the veins because in the other region
i.e., the cells, the two layers of the integument are closely appressed
to one another
 Blood cells or haemocytes circulate in the wing immediately on
either side of the vein
Numerous cross veins facilitate the complete circulation of
haemolymph in the wings
The wings articulate dorsally with the anterior and the posterior notal
wing processes and ventrally with pleural wing processes
As per the hypothetical generalized pattern of wing venation, major
longitudinal veins have been identified by their location relative to
one another their form, their association with basal sclerites and the
presence of trachea

5. This understanding is further strengthened by information from the
study of fossil insects
The margins of the wings are named as followes:
1. The anterior margin or costal margins
2. The posterior margin or anal margin
3. The outer margin or apical margin
Insects exhibit considerable diversity in the pattern of wing venation
among different group of insects
Though their functional significance is little known, the pattern of
wing venation is very useful to identify the insects

7.  Several venation terminologies are in use
and the most widely used has been the
Comstock or comstrock – Needham
system
 According to this system there are a
series of six major longitudinal wing
veins
 They are :
1. Costa (Cu2) 2. Subcosta (Sc)
3. Radius (R) 4. Media (M)
5. Cubitus (Cu) 6. Anal (A)
Except costa other veins may branch
The subcosta may branch once
The branches of the
longitudinal veins are numbered from
anterior to posterior around the wing by
means of subscript numerals for example
the two braches of subcosta are designated
as Sc1 and Sc2

8. Anterior branch of the radius is R1
The radial sector may fork twice, with four branches reaching the
wing margin
The media may fork twice with four branches reaching the wing
margin
Cubitus forks twice into Cu1 and Cu2 or Cu1 forks again distally
into Cu1a and Cu1b
The anal veins are typically unbranched and are usually
designated from anterior to posterior as the first (1A), second
(2A), third (3A) and so on

9. The cross veins contact the major longitudinal veins and are usually
naked accordingly for example, the medio – cubital cross vein is
named as m – Cu
Some cross veins have special names e.g. humeral cross vein (h),
sectorial cross veins (s) etc
The space in the wing between the veins are called the cells
The cells may be open cells i.e., extending to the wing margin or
closed cells i.e., completely surrounded by veins
The cells are named according to the longitudinal vein on the
anterior side of the cell for example , i.e., open cell between R2 and
R3 is called R2 cells

10. 1. Number
2. Size
3. Venation
4. Function and texture
5. Wing coupling mechanism
6. Resting Position
7. Colouration
8. Hairs and Scales in wings

11. Aphid
(Homoptera)
Bug (Heteroptera) Termites
(Isoptera)
Thrips
(Thysanoptera)
Butterfly (Lepidoptera) Beetle
(Coleoptera)
Wasp
House fly
(Diptera)

12. If two cells are separated by a cross vein, i.e., cells have common
name but they are individually designated by number for example,
i.e., medial cross vein connects M2 and M3 and divides the M2 cell
into two cells namely first M2 cell(Basal cell) and the second M2cell
(distal cell)
If a cell is anteriorly bordered by fused vein, it is named after the
posterior component of that fused vein for example, the cell bordered
by R2+R3 is called the R3cell
In the more primitive, generalized insect order such orthoptera, the
wings fold in a pleated fashion so that the longitudinal veins lie on
top of the crests (convex veins) or within troughs (concave vein)
Concave veins are always concave and Convex veins are always
convex for example the main stem of the radius is always convex

13.  The number of pairs of wings varies in different insects
Insects may possess a single pair of wings (Diptera, Pterygota), two
pairs (Pterygota other than Diptera) or none at all (Apterygota)
There are many secondary wingless pterygotes (e.g.fleas) i.e., their
ancestors had wings but the ancestors of apterygotes never had
wings (apterous)
There are pterygotes with minute wings (micopterous), reduced
wings (brachypterous) and fully developed wings (macropterous or
alate)

14.  The size of the wings ranges form being extremely minute (e.g.
wasps, Hymenoptera and flies) to quite large (e.g. atlas moth of
Australia has wing span of 35 cm)
In many insects there is a tendency for the hind wings to be smaller
than the forewings e.g. may fly (Ephemeroptera)

15. As observed for the size, the wing venation also varies from the
extensively reduced and simplified (e.g. wasps) to the highly
complex net work (e.g. dragonflies and damselflies, Odonata)
Veins also vary in thickness from quite thick (Periodical cicada,
Homoptera, Hemiptera) to vary thin and delicate ( Scorpionflry,
Neuroptera)

16. Although the Primary function of the wing is flight, they have been
modified to perform different functions
In beetles the membranous hind wings are folded beneath the hard
protective forewings called elytra (Sing. elytron)
Among Heteroptera (Hymenoptera) the forewings are hardened
apically and membranous distally containing veins called the
hemelytra (hemelytron) or half elytron

17. The forewings of orthopterans are parchment – like and
probably afford protection to the hind wings and are referred
to as tegmina (sign. tegmen)
 In several insects, the wings are employed to produce sound
e.g. field cricket

18. In pterygotes with two pair of wingsthe forewings andhind wings
may work independaently (Odonata, Ephemeroptera and
Neuroptera) or they may remain coupled to one another in various
ways and both of them on one side act as an unit
For example, in hymenoptera, the two wings on one side are coupled
by spine – like frenulum or lobe – like jugum
In insect with wing coupling mechanism, the hind wings are usually
somewhat smaller than the forewings
The tendency toward reduction of the hind wing have reached its
zenith in Diptera and the remnants have developed into the
balancing organs , halteres

20.  The position of holding the wings at rest also varies.
Members of the primitive orders such as Ephemeroptera and
Odonata do not have wing coupling mechanism and they are unable
to flex the wings over their abdomen and hence when at rest hold
them vertically over their dorsum (e.g. mayflies and dragon flies) or
horizontally (e.g. dragonflies)
Many insects can flex the wings over their abdomen at rest
Many homopterans and neuropteran hold the wings in the form of a
roof over their abdomen

21. Many insects have hyaline (Clear) or opague, un-pigmented wings
However, others have wing colouration due to pigmentation within
the integument (e.g. dragonflies) itself or to a covering of minute
pigmented scales or the covering scales may physically resemble
thin layers of diffraction grating in their effects upon impinging light
(Butterflies and moth)
The colouring pattern often enables the insects to camouflage and to
gain protection from predators
Industrial melanism is a special feature of colouration of adaptive
significance

22. The scales in Lepidoptera are modified setae
In many other insects, the wings have macrotrichia and microtrichia
Generally, the macrotrichia are randomly scattered over the surface
whereas the microtrichia (true setae) tend to be concentrated along
the major veins and their branches
Thus, the distinct rows of microtrichia, in the absence of veins, are
considered as the location of vein that has been lost.

23. Hence, microtrichia are useful to understand the evolutionary
changes in wing venation
The macrotrichia along the veins are probably mechanoreceptros
responding to touch and possibly to the flow fo air over the wing in
flight
 Wing bases possess several campaniform sensilla, generally three
group on the underside of the subcosta and three on the dorsal sdie
of the radius
Campaniform sensilla are also scattered on the distal veins and they
have no direction sensitivity
Chordotonal organs are also present at the wing base
In orthopetran each wing base has stretch receptor and a chordotonal
organ