Download - How do Long-range Insect Migrants Control their Flight ... · How do Long-range Insect Migrants . Control their Flight Direction? ... Desert Locust. North Africa: 10. 9 –10. 11.

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 <1 ms-1

• Wind speeds usually exceed this a few m above the ground

• Recognition of FBL – Taylor (1974)

• Downwind movement most efficient at high-altitudes

• 10 – 20 ms-1 achieved at just a few 100 m

• Most migrants fly above their FBL

• A few well-studied large insects migrate predominantly within it

Taylor (1974) Insect Migration, Flight Periodicity and the Boundary Layer. J. Anim. Ecol.

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 = 193°P < 0.001

Clear Skies

N = 27 individualsR = 0.09No mean directionP = 0.813

Overcast Skies


Time Compensation?Rebecca Nesbit


Control Group


Clock-shifted


Flight Towards the Sun?Rebecca Nesbit


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 = 354°R = 0.66P < 0.001

Wind Directions

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

FlightHeadings

N = 78 Events (20,000+ moths)Mean Direction = 18°R = 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 = 169°R = 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 = 195°R = 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 Office’s 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)