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The ecology of Ribautodelphax imitans (Ribaut.): a seldom recorded planthopper in the UK

By Alex D. K. Dittrich


This study is primarily concerned with the ecology of Ribautodelphax imitans (Ribaut.), a\ud seldom recorded, data deficient and rare species of planthopper (Delphacidae:\ud Auchenorrhyncha: Hemiptera) in the UK. Although it dealt with the ecology of this one\ud species, it explored its community, related species and how they respond to habitat, host\ud plants, and each other.\ud Firstly this project looked at the community position of R. imitans over a single\ud season, clarifying its numerical abundance related to other species in its community. The\ud lifecycles of many species could be modelled over the year; delphacids and cicadellids\ud were mostly synchronous within each family. Monitoring the site over the course of\ud several years also highlighted co-abundance patterns with a related planthopper\ud Javesella pellucida (Fab.), which opened up avenues for experiments and comparisons\ud between this species and R. imitans.\ud Host plant associations of R. imitans were investigated, as were the associated\ud host plant networks of the Auchenorrhyncha community. It was determined that R.\ud imitans was monophagous on tall fescue Schedonorus arundinaceus, but the community\ud was dominated by generalist species. It was determined that in this typical grass feeding\ud Auchenorrhyncha community, plant diversity was not the main driver for species richness\ud however it was probably a factor in its stability. As tall fescue was the dominant grass on\ud the study site, Coe Fen, it was determined that structures associated with this grass,\ud tussocks, were important in the Auchenorrhyncha community.\ud Tussocks were investigated using survey and experimental manipulation\ud approaches. Firstly the role of tussocks in grassland appeared to ameliorate the negative\ud effects of declining sward height outside of tussocks - as a result of cutting and grazing -\ud as more insects were found in tussocks surrounded by shorter swards than long.\ud Secondly, there were contrasting responses of different groups to different aspects of\ud tussock structure, it was thought that delphacids prefer denser and more nutrient-rich\ud areas, whereas cicadellids prefer more open and less nutrient-rich areas of sward. These\ud may relate to both their nutritional physiology and their biomechanics. The strong fidelity\ud towards tussocks of its host plant could increase conspecific heterosexual encounters of\ud R. imitans, thus maintaining high local population size and natality.\ud Lastly, interactions between and within species were investigated in a series of\ud lab-based experiments. No effect of conspecific or allospecific density could be attributed\ud to a change in developmental rate. However, there was evidence of host plant shifting in\ud the generalist J. pellucida caused by the presence R. imitans.\ud The combination of host plant specificity, habitat specificity and competitive\ud dominance feed into a model that would explain how rare species, or low-density\ud populations can persist. However without fully understanding the distributions of species,\ud one cannot be fully certain of its real distribution and status. This thesis provides a clear\ud understanding of aspects of the species’ general ecology, thus helping advise on how to\ud collect further national records of this species, unlocking the key to its true status

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