2. When locust become gregarious they are extremely destructive

3. Locust flight as a model system Can maintain flight for many hours 2 sets of wings: Fore wings (second thoracic segment) Hind wings (third thoracic segment) Fore/hind wings beat slightly out of phase (7ms) Beat stroke is complex Wing beat @ 20 Hz To fly the locust must solve: Lift (the ability to maintain a flight force) Control (the ability to change velocity/direction) Correction (the ability to respond to external forces)

4. Comparison of insect wing beat frequencies

5. Locust (insect) flight Basic behavioral experimental setup (old school)

6. Locust (insect) flight Modern and high tech behavior and neurophysiology

7. Locust (insect) flight High tech behavior and neurophysiology

8. The wing beat cycle: Hindwing precedes the forewing in each wing beat cycle. Hindwing stroke greater in amplitude Depressor and elevator muscles initiate each phase of the cycle Forewing depressor muscle activation lags behind hindwing depressors.

9. Wing movement and flight forces are complex but rythmic Angle of wing: Horizontal on down stroke Vertical on upstroke Moves forward on down stroke, back on upstroke Up/down stroke movements develop vortices Wing pushes against vortices producing thrust on both strokes

10. The flight muscles and nervous system involved with flight Wings are mounted on hinges Hinges contain proprioreceptors that indicate wing position/angle Each wing equipped with several depressor and elevator muscles Control up/down strokes and angle of attack Flight muscle rhythm controlled via TG1-TG3 Brain: Initiates flight Mediates flight rhythm rate and flight surface angle based on sensory feedback

11. Innervation of the major flight muscles across 3 TGs. Muscle control: One to multiple neurons per muscle Ipsilateral and contralateral innervation controlled by TG1-3 Motor units are distributed over a broad area

12. Neural control of flight muscles Neural activity from motor neurons are periodic or oscillatory Forewing lag evident in depressor motor neuron activity Nevertheless both fore and hindwing motor neurons are coordinated

13. The concept of the chain reflex A chain reflex takes sensory input (S) arising from one reflexive behavior (R) and to initiate another behavior: R 1 triggers an S 2 S 2 triggers R 2 R 2 triggers S 1 and so on… Assumes sensory input drives patterned responses This is not how locust produce wing beat patterns Removal of sensory input will reduce wing beat frequency (from 20 to ~10Hz) but does not influence its pattern. Is it a CPG or something simpler? Proprioreceptors

14. “Phase-locked” interneuron motor neuron and muscle activity Figure shows a single muscles activity (M112, a depressor muscle) Depressor motor neuron (MN128) positively correlates to M112 contraction Motor neuron (MN83; elevator neuron) is negatively correlated to M112 contraction Interneurons (IN301 IN511) are also phasic and correlated to muscle activity IN301 and IN511 have different phase relationships to M112 Point: Sensory input mediates wing beat frequency but the generation of the pattern is central.

15. Simple CPG

16. IN301 active during wing elevation Excites IN501 IN501 active during wing depression Inhibits IN301 Circuit forms the basis of an oscillatory CPG Locust flight CPG core

17. Locust flight CPG core with input and output

18. Locust flight CPG core with input and output and a delay

19. The CPG circuit (expanded). Does not show descending input IN301 indirectly excites IN501 by inhibiting inhibitors of IN501 IN501 directly and indirectly (by inhibiting exciters of IN301) inhibits IN301