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

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

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

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

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

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

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

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 B. Flight Mechanism Is Complex and Involves

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

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

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

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

Contraction Times of Invertebrate Muscle Source Time (seconds) Anthozoan muscles5-180 Scyphozoa Earthworm Circular Muscle Bivalve Byssus Retractor Muscle 1 Gastropod Tentacle Retractor 2.5 Horseshoe Crab Abdominal Muscle Insect Flight Muscle (striated)0.025 ~ 40 contractions per second!

Insect BeatsFlight 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 fly to 300

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)

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

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

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

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

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

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

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

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

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. Rotational Vortex Leading Edge Vortex Rotational Vortex Vortex Video

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.

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).

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

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

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?

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

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?

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

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