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Accueil du site → Doctorat → Royaume-Uni → 1999 → Small-scale environmental factors and Desert locust behaviour and phase state

University of Oxford (1999)

Small-scale environmental factors and Desert locust behaviour and phase state

Despland, Emma

Titre : Small-scale environmental factors and Desert locust behaviour and phase state.

Auteur : Despland, Emma.

Université de soutenance : University of Oxford

Grade : Doctor of Philosophy (Ph.D.) : 1999

New methods were developed to assign quantitative, measurable indices to vegetation distribution and to locust behaviour phase state. Resource distribution was represented via fractal dimension (see chapter 2) ; a simplified version of Roessingh et al.’s (1993) phase assay was designed for use in the field (see chapter 6).Chapter 3 describes laboratory experiments in which locust nymphs were exposed to different patterns of natural food resource in an arena, after which their behavioural phase state was assayed. When the distribution of the resource was patchy, locusts were more active, experienced higher levels of crowding, and became more gregarious. Chapter 4 describes similar laboratory trials as chapter 3, but uses chemically defined synthetic foods to study the effects of food distribution and nutritional quality. The diets were : rich and balance, dilute and balanced, or a choice of unbalanced foods. Gregarisation was most pronounced in the dilute diet treatment, due to an interaction between crowding and locomotion.Chapter 5 shows that both visual and olfactory stimuli from conspecifics are involved in the attraction/repulsion response of gregarious and solitarious locusts. Quantifiable behavioural differences also existed between solitarious and gregarious locusts in an empty arena. This result paved the way for the development of a field phase assay without stimulus insects (see chapter 6).Field studies were conducted in Mauritania to study under natural conditions the action of the mechanisms investigated in the laboratory. The behaviour of nymphs in an outdoor arena placed on natural vegetation depended on weather conditions and on the species and distribution of the vegetation. Phase differences were not detected (see chapter 7).

Mots Clés : Locusts ; Population density ; Swarm formation Zoology Ecology

Annonce : EThOS (UK)

Accès au document : Proquest Dissertations & Theses

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