Behavioural and Physiological Plasticity during Phase Change in the Desert Locust

by

ACKNOWLEDGEMENT

I would take this opportunity to thank my research supervisor, family and friends for their support and guidance without which this research would not have been possible.

ABSTRACT

The aim of studying it is to get insight in to Desert Locust. The main theme is to investigate the spatial distribution patterns of newly hatched locust nymphs in a setup that simulated seminatural conditions, without any previous manipulation other than parental density, and thus to reveal their innate or default behavioral phase. Such innate behavior is crucial for our understanding of locust natural history and locust outbreak dynamics.

DECLARATION

I, [type your full first names and surname here], declare that the contents of this dissertation/thesis represent my own unaided work, and that the dissertation/thesis has not previously been submitted for academic examination towards any qualification. Furthermore, it represents my own opinions and not necessarily those of the University (Bardhan, 2001, 467).

Signed __________________ Date _________________

TABLE OF CONTENTS

CHAPTER 1: INTRODUCTION1

1.1 Aim of the study2

CHAPTER 2: LITERATURE REVIEW3

2.1 Phases of Locusts4

2.2 Why phase change in locust?7

2.2.1 Behavior8

2.2.2 Biology8

2.2.3 Morphology9

2.2.4 Physiology9

2.2.5 Habits9

2.3 Differences between gregarious and solitarious locusts10

2.4 Why Do Locust Swarm13

CHAPTER 3: MATERIALS AND METHODS15

3.1 Locust colony15

3.2 Locust phases15

3.3 Obtaining the experimental animals16

3.4 The test arena16

3.5 Data acquisition and analysis17

CHAPTER 4: RESULTS19

4.1 Nymph behavior upon hatching19

4.2 Hatchling spatial distribution20

4.3 Analysis23

CHAPTER 5: CONCLUSION26

References28

CHAPTER 1: INTRODUCTION

Since Uvarov's (Uvarov, 1921) revision of the genus Locusta that led him to suggest his theory of locust phases and to renounce the taxonomic distinction between the swarming and the solitarious forms of several locust species, locust phase polymorphism has been one of the most striking examples of environmentally induced phenotypic plasticity. It involves density-dependent differences in coloration, morphometry, food selection, metabolism, egg mass, reproductive physiology, neurophysiology, endocrine physiology, molecular biology, immune responses, longevity, pheromone production, and behavior (recent reviews by Simpson et al., 2005; Verlinden et al., 2009; Pener & Simpson, 2009). A remarkable example of such plasticity in behavior has been found in Schistocerca gregaria (Forskål), the desert locust, which was extensively studied in this context, partially due to its potential as a devastating pest (Sword et al., 2010). Gregarious S. gregaria are characterized by a strong attraction to conspecifics, which translates to active aggregation behavior (Ellis, 1963; Uvarov, 1966). They are also generally more active than solitarious locusts, including their strong propensity to wander in huge bands of marching hoppers or in flying swarms of adults. Solitarious locusts, in contrast, are more sedentary and cryptic in both morphology and behavior, and both nymphs and adults actively avoid contact with other locusts (Roessingh, 1993; Simpson et al., 1999).

They do not march and fly less (Fuchs et al., 2003). Solitary-reared locusts have been reported to acquire most of the behavioral characteristics of the gregarious phase within 4-8 h of crowding, including the propensity to aggregate, and thus reinforce the gregarizing stimuli provided by other locusts (Simpson et al., 1999). Recently, it has been shown that even a 30 min exposure of a solitary-reared nymph ...