1. Insect Flight
A. Wing Structure
Flight Mechanism
Evolution of Flight

2. Wings tend to have less venation and be more stiff in insects with
epidermis
Wings tend to have
less venation and
be more stiff in
insects with
faster wing speed
cuticle
epidermis
cuticle
cuticle

3. Not all hexapods have wings
-- 5 primitive orders have never developed wings
(known as Apterygote insects)
ex. collembolans, springtails
-- highly specialized insects without wings
parasites such as fleas and lice
castes of social insects--worker ants, termites
--functional wings occur only in the imago

4. Wings don’t operate in the same way in all insects
Examples:
-- dragonflies and grasshoppers: 2 pair of wings beat at the same frequency but not necessarily in synchrony

5. Wings don’t operate in the same way in all insects
-- Coleoptera, front wings have become heavy shields (elytra) and only hindwings serve for flight.
--Hemiptera ,forewings only hardened near base, membranous distally
Coleoptera
Hemiptera

6. Wings don’t operate in the same way in all insects
-- butterflies and moths, bees and wasps: wings are interlocked and their strokes are in synchrony

7. Wings don’t operate in the same way in all insects
Example:
-- diptera: front wings used in flight; 2nd pair modified as halteres, which act as a gyroscope to provide balance
Robber fly

8. Figure 1 Halteres, the 'gyroscopic' sense organs of the blow fly Calliphora vicina. During walking and flight, the halteres oscillate in a vertical plane around a proximal hinge, and Chan et al.3 have now shown that they are under both neural and visual control. a, The halteres (arrowhead) are found between the thorax and abdomen of a fly. b, Left haltere from above. Most of the mass of the haltere is in the knob (left). A thin, stiff stalk leads to a base that houses about 335 cuticular strain receptors

9. Insect Flight A. Wing Structure B. Flight Mechanism
C. Evolution of Flight
Dragon fly flight
Wasp in flight
Mosquito in flight

10. Is Complex and Involves
B. Flight Mechanism
Is Complex and Involves
Flight muscles that aren’t part of the wing
Elastic property of a substance called resilin present in the hinges of wings
(and in joints in the wing to add elasticity)
Elastic properties of the thorax itself

11. 1. Thorax-Wing Structure
3 thoracic segments, 2nd and 3rd bearing wings
Each segment is comprised of:
wing
notum
a) a dorsal plate called a notum
b) ventral plate called a sternum
c) 2 side plates, each called pleurons
pleurons
apodemes
Apodemes serve as interior
attachment sites for muscles
sternum

12. Thorax-Wing Structure
The wings are attached to the
thoracic segments at 3 points:
anterior notal process (notum)
posterior notal process (not shown)
3 pleural wing processes (pleuron)
wing
notum

14. Thorax-Wing Structure
Schematic view
(dorsal plate)
(side
plate)

15. 2. Flight muscles: there are 2 types
Direct : attached to the wing itself
Indirect: not attached to the wing but to the
notum (dorsal) and sternum (ventral)
Direct
muscles
indirect muscles

16. Contraction Times of Invertebrate Muscle Source Time (seconds)
Anthozoan muscles
Scyphozoa
Earthworm Circular Muscle
Bivalve Byssus Retractor Muscle 1
Gastropod Tentacle Retractor
Horseshoe Crab Abdominal Muscle
Insect Flight Muscle (striated)
Striated muscles can contract much faster than smooth muscle. Without striated muscles insects would not be able to fly.
~ 40 contractions per second!

17. Insect Beats Flight speed /second km/hour
Dragonfly
Beetles
Butterflies
Hawk moth
Mosquito
Midges
Honey bee
Movement - body lengths per second
human - 5
Volkswagen 'beetle' - 5
jet fighter plane - 100
fly to 300

18. In all insects, the upstroke is affected by contraction of
indirect flight muscles; this results in the notum being
pulled down toward the sternum. A fulcrum point
at the pleural process forces the wing up
(indirect)

19. With the relaxation of the indirect muscles
In butterflies and moths, beetles, grasshoppers, roaches, dragon flies and others, the downstroke is powered by the direct flight muscles in conjunction
With the relaxation of the indirect muscles
End of upstroke Downstroke

20. the dorsal longitudinal muscles
In insects such as bees, wasps, and flies the downstroke is also achieved by indirect muscles called
the dorsal longitudinal muscles
Stretch-
activated
muscles

21. 3. Neural control of wing movement:
synchronous: single volley of nerve impulses
stimulates a single muscle contraction and
therefore one wing stroke
asynchronous: only occasional nerve impulses are necessary to maintain wing movement. Storage of potential energy in the resilient part of the thoracic cuticle causes multiple wing strokes after a single muscle contraction; interaction of antagonistic indirect flight muscles is also important

22. Wing hinge contains Resilin, an elastic protein that returns Nearly 95% of the Kinetic energy that is delivered to it.
Insects with asynchronous control generate much faster wing speeds: flies 300 beats/sec midges 1000 beats/sec
Butterflies, which have synchronous control: 4 beats/sec

23. Basic principles of fixed wing aerodynamics fail to explain how some insects achieve flight … i.e. bumblebees

24. Lift and Thrust Flying is more than upward-downward wing strokes.
For effective flight the angle of the wing on the upward
and the downward stroke cannot be the same.
Direct muscles alter the angle of the wing to
maintain a net thrust.
View
of the leading
edge angle of
the wing
during the up
and down
strokes of
a flying insect
Lift and Thrust

25. Flow visualization Flying is more than upward-downward wing strokes.
For effective flight the angle of the wing on the upward
and the downward stroke cannot be the same.
Direct muscles alter the angle of the wing to
maintain a net thrust.
Flow visualization
Bumble bee flight

26. According to the most recent studies, the
insect wing stroke provides lift in 4 ways, three of which were previously unknown :
-- as a “classical” airfoil
-- by generating vortices behind the leading edge
-- rotational lift
-- wake capture

27. Rotational
Vortex
Leading
Edge Vortex
Rotational
Vortex
till Image of hovering vortices. In general, cool colors represent clockwise motion and warm colors counterclockwise. The figure-8 motion of the wing (shown here in black, with the leading edge toward the Y axis) has produced clockwise (blue and green) as well as counterclockwise (red) vortices.
Vortex Video

28. DOWNSTROKE. In this example, as a fly moves from right to left during a downstroke of its wings (top),blue arrows indicate the direction of wing movement and red arrows the direction and magnitude of the forces generated in the stroke plane.
During this phase, the insect has at its disposal two means of generating lift. Delayed stall (1) causes the formation of a leading-edge vortex that reduces pressure over the wing. Rotational lift (2) is created when the insect rotates the angle of its wings (dotted line), creating a vortex similar to that of putting "backspin" on a tennis ball. At its completion (3), the maneuver also results in a powerful force propelling the insect forward.

29. UPSTROKE. As the insect drives its wing upward, it has the option of using another mechanism to gain lift--wake capture. This gains an insect added lift by recapturing the energy lost in the wake. As the wing moves through the air, it leaves whirlpools, or vortices, of air behind it (4). If the insect rotates its wing (dotted line), the wing can intersect its own wake and capture its energy in the form of lift (5).

30. Insect Flight A. Wing Structure B. Flight Mechanism
C. Evolution of Flight

31. Evolution of Wings: not well understood.
Earliest insects included both flying and non flying types
There are two theories:
1) paranotal theory: wings developed from paranotal
lobes that were first used for gliding. But how did
flight musculature originate?
Fossil insects with
paranotal lobes

32. Evolution of Wings: not well understood.
Earliest insects included both flying and non flying types
There are two theories:
1) paranotal theory: wings developed from paranotal
lobes that were first used for gliding. But how did
flight musculature originate?
2) branchial theory: wings developed from
gills that were subsequently used for swimming, and finally for flight.
WHAT IS THE EVIDENCE?

33. Skims the surface of streams
Mayfly ancestors were probably the first flying insects
Some species with reduced wings (brachyptery) are unable to fly and use wings as fins for swimming
Comparisons with fossils indicate that brachyptery may have been common in early insects
Madagascar
Mayfly
Skims the surface of streams

34. Evolution of Wings: not well understood.
Earliest insects included both flying and non flying types
There are two theories:
1) paranotal theory: wings developed from paranotal
lobes that were first used for gliding. But how did
flight musculature originate?
2) branchial theory: wings developed from
gills that were subsequently used for swimming, and finally for flight.
WHAT IS THE EVIDENCE?

35. Discussion of Molecular Evidence: expression of pdm/nubbin
and apterous genes
Everof and Cohen 1997 Nature

36. Pdm nubin expression in book gills and book lungs of chelicerates
Darmin Saviraki and Everof
2002
Current
Biology