• Admin
    UC Research Repository
    View Item 
       
    • UC Home
    • Library
    • UC Research Repository
    • College of Science
    • Science: Theses and Dissertations
    • View Item
       
    • UC Home
    • Library
    • UC Research Repository
    • College of Science
    • Science: Theses and Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of the RepositoryCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsThis CollectionBy Issue DateAuthorsTitlesSubjects

    Statistics

    View Usage Statistics

    Frequency-dependent host choice by phytophagous insects and the evolution of plant defence strategies

    Thumbnail
    View/Open
    monks_thesis.pdf (7.548Mb)
    Author
    Monks, Adrian
    Date
    2000
    Permanent Link
    http://hdl.handle.net/10092/4766
    Thesis Discipline
    Botany
    Degree Grantor
    University of Canterbury
    Degree Level
    Doctoral
    Degree Name
    Doctor of Philosophy

    Herbivore adaptation to plant resistance presents an evolutionary trade-off for plants. In the absence of plant resistance the plant is susceptible to non-adapted herbivores. However herbivores that are adapted to a particular plant resistance trait may increase the cost to the plant of expressing the trait if the herbivores use it as an attractant. The adapted herbivore escape hypothesis suggests that plants may get around this problem by only deploying the resistance when necessary in response to herbivore feeding. This hypothesis requires that adapted herbivore are able to discriminate in favour of resistant plants when making host choice decisions and that host selection is frequency-dependent such that the undamaged phenotype can escape when rare. This thesis set out to determine how host phenotype frequency affects choice by insect herbivores in both a mechanistic and a functional sense. In addition, a study was made of the conditions under which induced strategies may be evolutionary stable when under selection by adapted and non-adapted herbivores in the absence of physiological costs of defence. The role of learning and host-deprivation in the oviposition acceptance behaviour of the diamondback moth (Plutella xylostella L. (Lepidoptera: Yponomeutridae)) was investigated. Previous experience with a host plant increased acceptance in a host-specific way. Discrimination between host plants was independent of deprivation. Existing models of insect oviposition acceptance do not adequately explain these findings. A new model- The Incremental Acceptance Model- is proposed. In laboratory trials containing mixtures of damaged and undamaged Brassica oleraceae L. and B. napus L. plants at different frequencies, a key assumption of the adapted herbivore escape hypothesis was supported. The probability of oviposition by the diamondback moth was dependent on the frequency-of the damaged state and undamaged Brassica plants were more likely to escape herbivory than were damaged plants. The larval rearing plant affected the oviposition preference of the moths for damaged plants. The evolution of plant defence strategies was modelled under frequency-dependent selection by nonadapted and adapted, or partially adapted herbivores. A stable state always arose that contained both the defended and undefended plant phenotypes, except under certain restrictive conditions. Inducibility formed a pure ESS provided the defended phenotype was not fitter than the undefended phenotype and the plant defence reduced the feeding damage by non-adapted herbivores. In contrast with previous models, induction is not necessarily favoured when herbivory is predictable or the costs of expressing defence intermediate. It is argued that frequency-dependent herbivory is a major omission from previous studies of the evolution of plant defence strategies.

    Collections
    • Science: Theses and Dissertations [3603]
    Rights
    https://canterbury.libguides.com/rights/theses

    UC Research Repository
    University Library
    University of Canterbury
    Private Bag 4800
    Christchurch 8140

    Phone
    364 2987 ext 8718

    Email
    ucresearchrepository@canterbury.ac.nz

    Follow us
    FacebookTwitterYoutube

    © University of Canterbury Library
    Send Feedback | Contact Us