published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

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The scale insect predator Chilocorus nigritus is considered as one of the most successful and important biological control agents in classical biocontrol. The ladybird is currently a commercial product, used for scale insect control in glasshouse environments, but despite widespread success in wild field releases, use of the predator in glasshouses has achieved only moderate success. This study aimed to find out which factors may affect the success of C. nigritus in glasshouse pest control. Two key factors with potential to have a dramatic impact on the predator were identified; genetic variability within and between insect populations, and male killing endosymbiotic bacteria, known to have a diverse range of effects on up to 70% of all insect species. Beetle strains were sourced from several insectaries and geographical locations. DNA sequencing determined significant genetic differences between biotypes of C. nigritus from different localities, indicating that C. nigritus exists as a series of functional biotypes across its range. All biotypes were tested for Wolbachia, Rickettsia and Spiroplasma infections, identifying Rickettsia and Wolbachia presence in most populations. Uninfected sub-lines of these strains were therefore created via tetracycline treatment. A number of bionomic characteristics of the beetle were compared across these strains and infection types in order to assess the influence of genetics and bacterial endosymbionts. Significant effects of endosymbionts were noted in fecundity and prey consumption, and genetically distinct biotypes varied in their prey consumption. A combination of biotypes and infection types also provided successful suppression of scale insects in glasshouse trials at Royal Botanical Gardens, Kew, and beetles were shown to produce a defence pheromone similar to hippodamine, which could potentially be another strong influence on the species’ ecology. This thesis suggests that variability within a predator population may be an asset, rather than a hindrance.

As early as 1901, ecological and epidemiological studies were conducted to understand malaria transmission in the UK. Unfortunately, following the eradication of malaria after WWII, ecological studies on local mosquito species has been intermittent, leading to a significant gap in knowledge of the current habitat preference, distribution and vector capabilities of the 33 recorded species. This lack of current information makes the assessment of possible transmission of enzoonotic diseases such as Chikungunya and West Nile virus in UK difficult. Thus the overall purpose of this thesis was to facilitate the identification of potential vector species through the documentation and characterisation of the ecology of adult and larval stages, and the host selection of British mosquitoes, in southern England and northern Wales. A total of 13 out the 33 documented species are assessed in this study. Of which members of the Maculipennis and Pipiens Group comprised the bulk of the adult and immature collections respectively. The development of the ITS2 PCR-RFLP assay in this study allowed the identification of the three members of the Maculipennis Group, which revealed the widespread occurrence of the recently documented An. daciae in almost all localities sampled. While previously published assays discriminating the Pipiens Complex, did not yield congruent results questioning the prior identification methods and the validity of the taxonomic status of its members. In addition, host-specific primers designed herein to determine host selection in local mosquitoes revealed an indiscriminate host selection by An. atroparvus, An. daciae, An. messeae and Cx. pipiens thus indicating their potential role as vectors in the UK.

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