How do Long-range Insect Migrants Control their Flight Direction?

Jason W. ChapmanRothamsted Research, UK

Introduction

Class Species Location Numbers Biomass (tons)Insects Darner Dragonfly Argentina 4 6 Billion 4000

Monarch Mexico 200 Million 80Desert Locust North Africa 109 1011 200,000

Mammals Wildebeest East Africa 1.3 million 280,000Free-tailed Bat New Mexico 20 million 300

Holland, Wikelski & Wilcove (2006) How and why do Insects Migrate? Science

1. Enormous Numbers and Biomass

3. Simple Systems and Model Organisms

2. Crop Pests and Disease Vectors Orthoptera (e.g. locusts) Hemiptera (aphids & planthoppers) Lepidoptera (armyworms, cutworms & bollworms) Diptera (mosquitoes, midges & blackflies) Coleoptera (bark beetles)

Biometeorology of Migration

Weather hugely influential on insect migration patterns Wind speed & direction

Airspeeds of large insects about 3 6 ms-1

Airspeeds of micro-insects often

Seasonal Migration Patterns

Most insect migration is one-way

Return movements, if any, carried out by subsequent generations

Much movement nomadic by nature, but there are general directional trends In tropical & sub-tropical regions, movements related to rainfall In temperate regions, there is a tendency for north-south seasonal movements

Movements over the necessary distances requires favourable winds Poleward winds in the spring are warm and thus favourable for migration Equatorward winds are cool and so will tend to suppress migration

Led to the idea of the Pied Piper effect

Largely discounted now, return movements have been documented in many species

Natural selection may be expected to act very strongly on the autumn migration

Do Simple Rules Guide Migrations?

Selection of Favourable Winds in Green Darner Dragonflies in the Autumn

Wikelski et al (2006) Simple Rules Guide Dragonfly Migration. Biology Letters

Green Darner Dragonflies Anax junius Christian Ziegler

Migrate on days following cooler nights Fly downwind (tend to be northerlies, so southward movement) Re-orientated when faced with large water crossing Simple rules (like songbirds)

Monarch Time-compensated Solar Compass

Danaus plexippus

Mouritsen & Frost (2002) Virtual Migration in Tethered Flying Monarch Butterflies Reveals their Orientation Mechanisms. PNAS

Return Migration of Vanessa cardui

Painted Lady Vanessa cardui Ian Woiwod

Annual immigrant to UK from N Africa

Varying abundance

Good years: 1996, 2000, 2003, 2006

Evidence for return migrations?

Rebecca Nesbit

Nesbit, Hill, Sivell, Woiwod & Chapman (in prep)

Flight simulators in Gibraltar May 2006 Ian WoiwodPainted Lady Ian Woiwod

Flight Simulators

Mouritsen & Frost (2002) PNAS 99: 10162-10166

Orientation of Autumn MigrantsRebecca Nesbit

N = 94 individualsR = 0.32Mean direction = 193P < 0.001

Clear Skies

N = 27 individualsR = 0.09No mean directionP = 0.813

Overcast Skies

Nesbit, Hill, Sivell, Woiwod & Chapman (in prep)

Time Compensation?Rebecca Nesbit

N = 94 individualsR = 0.32Mean direction = 193P < 0.001

Control Group

N = 26 individualsR = 0.46Mean direction = 180P < 0.001

Clock-shifted

Nesbit, Hill, Sivell, Woiwod & Chapman (in prep)

Flight Towards the Sun?Rebecca Nesbit

Nesbit, Hill, Sivell, Woiwod & Chapman (in prep)

Vertical-Looking Radar (VLR)

Continuous coverage:150 1200 m

Individual insects:15 height bands

Parameters:Speed & direction

OrientationMassShape

0 m

600 m

1200 m

5 mg

15 mg

1 mg

500 mg

Chapman et al (2003) Vertical-looking Radar: A New Tool for Monitoring High-altitude Insect Migration. Bioscience

Orientation Mechanisms in High-flying Moths

Silver Y Autographa gamma

Annual migrant to N Europe from Med

Flies at heights of 200 m 1000 m

Layers correspond to regions of wind speed maxima

Can it have any control over its displacement direction?

Chapman et al (2008a) Wind Selection and Drift Compensation Optimize Migratory Pathways in a High-flying Moth. Current Biology

Chapman et al (2008b) A Seasonal Switch in Compass Orientation in a High-flying Migrant Moth. Current Biology

Spring Migration Events

Displacement Directions

N = 83 Events (20,000+ moths)Mean Direction = 354R = 0.66P < 0.001

Wind Directions

N = 108 eventsMean Direction = 197R = 0.29P < 0.001

FlightHeadings

N = 78 Events (20,000+ moths)Mean Direction = 18R = 0.17P < 0.001

Chapman et al (2008a) Current Biology 18: 514-518Chapman et al (2008b) Current Biology 18: R908-909

Autumn Migration EventsDisplacement

Directions

N = 96 Events (38,000+ Moths)Mean Direction = 169R = 0.39P < 0.001

Wind Directions

N = 121 EventsNo Mean DirectionR = 0.12P = 0.15

Flight Headings

N = 96 Events (38,000+ Moths)Mean Direction = 195R = 0.24P < 0.001

Chapman et al (2008a) Current Biology 18: 514-518Chapman et al (2008b) Current Biology 18: R908-909

Trajectory AnalysesLaura Burgin

Met Offices NAME Dispersion Model

Displacements HeadingsCompass-mediatedOrientation in Other Species

Large Yellow Underwing Noctua pronuba

Chapman et al (in prep)

Concluding Remarks

Not passive or accidental movements

Central role for behaviour

Complicated & sophisticated strategies

Behaviour often inferred from observations of migration patterns

Need for experimental approaches

Acknowledgements

Ian Woiwod, Alan Smith, Joe Riley, Duncan Sivell, Rebecca Nesbit (Rothamsted)

Don Reynolds (University of Greenwich)

Henrik Mouritsen (University of Oldenburg)

Jane Hill (University of York)

Curtis Wood, Janet Barlow (University of Reading)

Laura Burgin, Peter Clark (Met Office)

Funding (BBSRC)

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