Experimental Characterization of the Structural Dynamics and Aero-Structural Sensitivity of a Hawkmoth Wing Toward the Development of Design Rules for Flapping Wing Micro Air Vehicles

A case is made for why the structures discipline must take on a more central role in the research and design of flapping-wing micro-air-vehicles, especially if research trends continue toward bio-inspired, insect-sized flexible wing designs. In making the case, the eigenstructure of the wing emerges as a key structural metric for consideration. But with virtually no structural dynamic data available for actual insect wings, both engineered and computational wing models that have been inspired by biological analogs have no structural truth models to which they can be anchored. An experimental framework is therefore developed herein for performing system identification testing on the wings of insects. This framework is then utilized to characterize the structural dynamics of the forewing of a large sample of hawkmoth (Manduca Sexta) for future design and research consideration. The research also weighs-in on a decade-long debate as to the relative contributions that the inertial and fluid dynamic forces acting on a flapping insect wing have on its deformation (expression) during flight. Ultimately the findings proves that both affect wing expression significantly, casting serious doubt on the longstanding and most frequently cited research that indicates fluid dynamic forces have minimal or negligible effect

Design of low density bio-inspired structures

This study involves the development of novel methods to enhance structural efficiency in the development of high performance lightweight stiff metal mechanical components. Optimised designs are created from biologically-inspired templates, taking advantage of new additive manufacturing techniques which enable the realisation of more complex shapes. The study focuses on the numerical side of design development and evaluation. Two case studies of aerospace components are considered: first, of an aircraft engine nacelle and second, of turbine blisks. In the first study, rib stiffeners, based on fibre arrangement in plant stem cells, are introduced and their geometric features are optimised for mass minimisation with mechanical response constraints done via genetic algorithms coupled with finite element analysis. The displacements of the optimised nacelle are lower compared to the original. Mass has lower optimisation emphasis, thus final values approach the mass limit. Optimised designs from different loading cases and magnitudes thereof have similar physical features. In the second study, turbine blisks are redesigned with an internal foam structure based on cancellous bones. Optimised 3D foam blisks are developed evaluated against the original solid design and with a different foam type. A study undertaken on 2D foam discs under inertial load demonstrates that foam configuration and densification methods influence the mechanical responses. The thesis shows that viable biologically-inspired designs can be developed using optimisation techniques. In both cases remarkable mass reduction is achieved while remaining within mechanical constraints. The Pareto front is traced on the design space from optimisation results, representing the set of optimal designs rather than a single unique solution. In the nacelle the displacement contour heavily influences the rib layout, which prefers intersections at boundary condition sites. The weight-to-displacement ratios of bio-inspired designs are lower than in equivalent topologically-optimised ones. In the turbine blisk, foam stiffness under inertial load is found to increase with node connectivity. Increasing relative density increases stresses but decreases displacement, and the specific behaviour is influenced by the method in varying density. In 3D the resulting foam blisks have higher stresses and displacement than the solid one, but their weight-to-displacement ratio can be improved using high-connectivity foams

Functional traits and resource-use strategies of native and invasive plants in Eastern North American forests

Despite the presumption that native species are well adapted to their local environment, non-native invaders seem to outperform native plants. Intuitively, it appears paradoxical that non-native species, with no opportunity for local adaptation, can exhibit greater fitness than native plants with this advantage. Here, I compared traits of native and invasive shrub and liana species in Eastern North American (ENA) forests to test the overarching hypothesis that non-native understory species invasive to this region have superior resource-use strategies, or alternatively, they share the same metabolic tradeoffs as the native flora. First, at a global scale, I addressed the largely untested hypothesis that biogeography places significant constraints on trait evolution. Reanalyzing a large functional trait database, along with species\u27 native distribution data, I found that regional floras with different evolutionary histories exhibit different tradeoffs in resource capture strategies. Second, using a common garden to control for environment, I measured leaf physiological traits relating to resource investments, carbon returns, and resource-use efficiencies in 14 native and 18 non-native invasive species of common genera found in ENA understories, where growth is presumably constrained by light and nutrient limitation. I tested whether native and invasive plants have similar metabolic constraints or if these invasive species (predominantly from East Asia) are more productive per unit resource cost. Despite greater resource costs (leaf construction, leaf N), invaders exhibited greater energy- and nitrogen-use efficiencies, particularly when integrated over leaf lifespan. Efficiency differences were primarily driven by greater mean photosynthetic abilities (20% higher daily C gain) and leaf lifespans (24 days longer) in invasive species. Third, motivated by common garden results, I conducted a resource addition experiment in a central NY deciduous forest to investigate the role of resource limitation on invasion success in the field. I manipulated understory light environments (overstory tree removal) and N availabilities (ammonium-nitrate fertilization) to create a resource gradient across plots each containing 3 invasive and 6 native woody species. Invasive species generally exhibited greater aboveground productivity and photosynthetic gains. After two treatment years, invasive species displayed more pronounced trait responses to the resource gradients, primarily light, relative to the weaker responses of native species. Lastly, I asked whether species exhibit similar resource-use strategies in their native and invasive ranges. I measured leaf functional traits of Rhamnus cathartica (native to Europe, invasive in ENA) and Prunus serotina (native to ENA, invasive in Europe) in populations across central NY and northern France. Notably, I found invasive US populations of R. cathartica had markedly greater photosynthetic rates (50% higher) and reduced leaf N resorption rates in autumn (30% lower) than native French populations. Contrastingly, I found minimal leaf trait differences in P. serotina between native (US) and invasive (French) populations. Collectively, my results highlight the utility of functional trait perspectives and support a mechanistic explanation for invasion success based on differential abilities of species to convert limiting resources to biomass

Bio-ecology of the African citrus triozid <em>Trioza erytreae</em> Del Guercio (Hemiptera: Triozidae) on citrus in Kenya : implication for its management

Citrus production is a major industry in Kenya. Apart from providing income and jobs, it contributes to food and nutritional security. For the last decade, citrus production has experienced a continuous decline, particularly in the Kenyan highlands. Consequently, production is unable to meet local demands, which has led to increased imports of citrus. Low production has been attributed to pest and diseases, of which the African citrus triozid (ACT) Trioza erytreae Del Guercio (Hem.: Triozidae) is the economically most important pest species due to its ability to vector “Candidatus Liberibacter africanus” (CLaf), the causal agent of the African citrus greening disease. Currently, the disease has no cure, hence the need to manage the pest in order to prevent the further spread of it. Through field surveys and laboratory studies, this thesis sought to determine the bio-ecology of ACT on citrus in Kenya and implications for its management. The results showed that ACT was widely distributed, causing more damage in shaded than unshaded citrus trees, particularly in the southeastern canopy quadrants. A newly developed predictive model revealed hotspots out of the distributional range under current and future climate scenarios. Trioza erytreae reproduction was confined to plants belonging to the family Rutaceae. Adult T. erytreae survived and reproduced on Zanthoxylum usamberensis (Engl.), Murraya koenigii (L.), Calodendrum capense(L.f.) Thunb., Teclea nobilis (Del.), Clausena anisata (Willd.) Hook. f. ex Benth. and Vepris bilocularis (Wright & Arn.) Engl. Also, plants which appeared to have superior host plant quality, as reflected by several of ACTs’ tested biological parameters, also produced adults with larger wing size and greater shape. Two host plants, i.e. V. bilocularis and T. nobilis, were reported here for the first time as alternative host plants for ACT. A spatial survey was conducted to assess seasonal variations of ACT occurrence across different altitudinal gradients with ACT populations significantly varying across different altitudinal gradients, resulting in higher pest densities in mid elevations (1,500-2,000 meters above sea level [m.a.s.l.]). The closely related Asian citrus psyllid Diaphorina citri Kuwayama (Hem.: Liviidae) was found and sampled in elevations up to 1,409 m.a.s.l. Yellow sticky card traps proved to be most efficient in trapping adult ACT. The result of a study to compare the effects of host plant quality on wing shape and size of ACT clearly showed that both geometric and traditional morphometry were useful in separation different populations of T. erytreae. The findings of this thesis thus provide relevant information to improve monitoring of ACT and to design ecologically sound integrated pest management strategies for control of this pest.Die Zitrusproduktion ist ein wichtiger Wirtschaftszweig in Kenia. Neben der Bereitstellung von Einkommen und Arbeitsplätzen trägt sie zur Lebensmittel- und Ernährungssicherung bei. Im letzten Jahrzehnt hat die Zitrusproduktion insbesondere im kenianischen Hochland kontinuierlich abgenommen. Folglich kann die Produktion der lokalen Nachfrage nicht gerecht werden, was zu einem zunehmenden Import von Zitrusfrüchten geführt hat. Der geringe Ertrag wird Schädlingen und Krankheiten zugeschrieben. Der wichtigste Schädling ist der Afrikanische Zitrustriozid (ACT) Trioza erytreae Del Guercio (Hem.: Triozidae) aufgrund seiner Fähigkeit "Candidatus Liberibacter africanus" (CLaf), den Erreger der Aftikanischen Zitrusgrünung, zu übertragen. Derzeit hat die Krankheit keine Heilung, daher muss der Schädling bekämpft werden, um eine weitere Ausbreitung der Krankheit zu verhindern. Durch Feld- und Laborstudien wurde versucht, die Bioökologie von ACT auf Zitrusfrüchten in Kenia und die Implikationen für die Bekämpfung des Schädlings zu bestimmen. Die Ergebnisse zeigten, dass ACT in beschatteten Zitrusbäumen stärker verbreitet war als in nicht beschatteten, insbesondere in den südöstlichen Baumkronenquadranten. Ein neu entwickeltes Vorhersagemodell beschrieb ‚Hotspots‘ außerhalb des derzeitigen Verbreitungsgebietes unter aktuellen und zukünftigen Klimaszenarien. Die Reproduktion von T. erytreae war auf Pflanzen der Familie Rutaceae beschränkt. Adulte ACT überlebten und reproduzierten auf Zanthoxylum usamberensis (Engl.), Murraya koenigii (L.), Calodendrum capense (L.f.) Thunb., Teclea nobilis (Del.), Clausena anisata (Willd.) Hook. f. ex Benth. und Vepris bilocularis (Wright & Arn.) Engl. Auf Pflanzen mit hoher Wirtspflanzenqualität entwickelten sich ACT mit größerer Flügelgröße und -form. Zwei Wirtspflanzen, V. bilocularis und T. nobilis, wurden zum ersten Mal als alternative Wirtspflanzen für ACT beschrieben. Eine räumliche Untersuchung wurde durchgeführt, um saisonale Variationen des ACT-Vorkommens über verschiedene Höhengradienten hinweg zu erfassen, wobei ACT-Populationen zwischen verschiedenen Höhengradienten mit höheren Schädlingsdichten in mittleren Höhenlagen (1.500-2.000 Meter über dem Meeresspiegel [M.ü.d.M.]) signifikant variierten. Die nahe verwandte asiatische Zitrusfrucht-Psyllide Diaphorina citri Kuwayama (Hem.: Liviidae) wurde in Höhen bis zu 1.409 M.ü.d.M. gefunden. Gelbe Klebe-Kartenfallen erwiesen sich als am effizientesten zum Fang von erwachsener ACT. Das Ergebnis einer Studie zum Vergleich der Effekte der Wirtspflanzenqualität auf die Flügelform und die Größe von ACT zeigte, dass sowohl die geometrische als auch die traditionelle Morphometrie zur Trennung verschiedener Populationen von T. erytreae geeignet ist. Die Ergebnisse dieser Arbeit liefern daher relevante Informationen zur Verbesserung des Monitorings und ACT zur Entwicklung von ökologisch verträglichen integrierten Pflanzenschutzstrategien gegen den Schädling

Adaptation to altitude in Heliconius butterflies

Local adaptation is an important process for studying recent evolutionary change. The environment changes drastically along steep clines, such as mountains, and diverse sets of challenges are predicted to drive local adaptation. Thus, these clines represent ideal settings to identify the traits and genomic mechanisms that allow some organisms to succeed across wide geographical ranges, which is a major goal of evolutionary biology. In this thesis I explore the environmental variables, phenotypic traits, and genomics underlying adaptation to altitude in the Heliconius butterfly genus. Firstly, using a collection of over 3500 wings I discovered that wing morphology varies predictably across elevations, with species and populations in the highlands having rounder wings than those in the lowlands. This study also highlighted that life-history, whether larvae are gregarious or solitary, determines the direction of wing sexual size dimorphism across species. Secondly, to understand the microclimates experienced in the wild by Heliconius butterflies, I measured hourly temperature and humidity for a full year in 28 sites across elevations and microhabitats on both sides of the Andes. The canopy greatly buffered the climate within the forest, but publicly available datasets failed to accurately predict these temperatures. Further, I found that species inhabiting higher altitudes were less tolerant to heat in the wild, while common-garden reared individuals of H. melpomene were equally tolerant after one generation, showing plasticity for this trait. Thirdly, with a dataset of over 600 whole-genome sequenced H. erato and H. melpomene individuals from four elevational clines, I found many parallel signatures of local adaptation to high altitude across clines and sides of the Andes, especially within H. erato. Finally, I studied the genomic basis of one of the traits I identified as being potentially involved in adaptation to altitude, wing shape. By combining common-garden rearing of highland and lowland populations of H. erato and H. melpomene and 666 whole-genome sequences from a published study, I found that wing aspect ratio is highly heritable, and identified relevant candidates for future functional studies. Overall, this work highlights that butterflies readily adapt to their local environment and that they do so in a more convergent fashion than previously thought. This thesis lays the groundwork for an exciting new branch of study for Heliconius research, where we combine the long fascination for their natural history and speciation, with new approaches to study how they adapt to the environment.University of Cambridge Earth System Science NERC Doctoral Training Partnershi