Phloem transport is along hydrostatic pressure gradients generated by differences in solute concentration between source and sink tissues. Numerous species accumulate raffinose-family oligosaccharides (RFOs) in the phloem of mature leaves to accentuate the pressure gradient between source and sinks. In this study, metabolic engineering was used to generate RFOs at the inception of the translocation stream of Arabidopsis thaliana, which transports predominantly sucrose. To do this, three genes, GALACTINOL SYNTHASE, RAFFINOSE SYNTHASE and STACHYOSE SYNTHASE, were expressed from promoters specific to the companion cells of minor veins. Two transgenic lines homozygous for all three genes (GRS63 and GRS47) were selected for further analysis. Sugars were extracted and quantified by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD), and 21-day old plants of both lines had levels of galactinol, raffinose, and stachyose approaching 50% of total soluble sugar. All three exotic sugars were also identified in phloem exudates from excised leaves of transgenic plants whereas levels were negligible in exudates from wild type leaves. Differences in starch accumulation or degradation between wild type and GRS63 and GRS47 lines were not observed. Similarly, there were no differences in vegetative growth between wild type and engineered plants, but engineered plants flowered earlier. Finally, since the sugar composition of the phloem translocation stream is altered in these plants, we tested for aphid feeding. When green peach aphids were given a choice between WT and transgenic plants, WT plants were preferred. When aphids were reared on only WT or only transgenic plants, aphid fecundity was reduced on the transgenic plants. When aphids were fed on artificial media with and without RFOs, aphid reproduction did not show differences, suggesting the aphid resistance is not a direct effect of the exotic sugars.

The temperature-dependent development of red and green morphs of the green peach aphid, Myzus persicae (Sulzer), was compared on flue-cured tobacco, Nicotiana tabacum (L.), at moderate to high constant temperatures in the laboratory. The red morph was found to develop faster and reproduce more than the green morph at temperatures that promoted the most rapid population growth of either morph. In addition, mean longevity of the green morph was increasingly and significantly shorter than the red morph as temperature increased above the mutual optimum temperature (25 °C) for population increase. Study of the growth of GPA populations on commercial flue-cured tobacco farms in Virginia indicated the initial GPA population is highly aggregated. As the population increases, it becomes increasingly more randomly dispersed within the field. The typical pattern of temporal development of GPA was a bimodal distribution with the greater proportion of individuals occurring after topping of the crop. Cumulative proportional population growth models using degree-days were able to adequately describe growth of populations only on individual farms. Study of the within-plant distribution of GPA found that populations developed colonies of greatest intensity on the youngest leaves. The proportion of the total GPA population found on each leaf occurring on the lower leaf surface decreased with ascending leaf position. In addition, the proportion of the total plant population found on the lower leaves was highest as the crop approached the topping stage. / M.S.

Field experiments with the green peach aphid on tobacco were conducted at Blackstone, Virginia in 1983 and 1984. The objectives were to: 1) confirm and identify source materials resistant to the green peach aphid; 2) study the inheritance of aphid resistance; 3) verify heritability of resistant genotypes through F2 and advanced generation testing and 4) investigate the nature of the resistance. Results showed green peach aphid resistance in Tobacco Introductions 1462, 1118, 1112, 1024, breeding line 1-35 and cultivar NC 745. Inheritance studies showed that the resistance is a recessive trait controlled by three separate, non-linked loci; such that a homozygous recessive at any one locus will condition for the resistance reaction. Among the source materials, one locus conditioned the resistance shown by TI 1118, TI 1112 and breeding line I-35. A second independent locus conditioned the found in TI 1024 and a third independent locus conditioned the resistance observed in NC 745. Tobacco Introduction 1462 possessed alleles for resistance at both the second and third loci. Small aphid cages were of questionable value for studying the resistance reaction. Higher leaf temperatures were noted for the caged leaf surfaces and may be responsible for the unreliable results. Evaluation of F2, F3, F5, F5 populations developed from resistant x susceptible crosses indicated that aphid resistance is a heritable trait and is not closely linked to adverse agronomic quality characteristics. / Master of Science

The effects of indigenous predators on green peach aphid (GPA), Myzus persicae (Sulzer), populations on flue-cured tobacco were evaluated in 1985 and 1986. The most common GPA predators found on tobacco were convergent lady beetle (CLB) (Hippodamia convergens), syrphid flies, Geocoris spp., Jalysus wackhimi, Nabis spp., Chrysopa spp., Micromus sp., and several other species coccinellids. However, CLB was the only predator that had a numerical response to increasing GPA density on tobacco. In the laboratory, the minimum number of GPA required to initiate reproduction in CLB, and the conversion rates were two factors that determined the oviposition rate of CLB. In fields, CLB demonstrated a sigmoid curve predator-prey relationship. CLB did not show a linear relationship until GPA populations reached a certain density. Furthermore, CLB did not show a response when GPA density was above the satiation point. Although CLB were able to reduce GPA population growth, they were not able to maintain GPA populations below the economic injury level. Two factors probably limited the success of CLB to control GPA populations on flue-cured tobacco: 1.) the glandular trichomes of tobacco which produced gummy exudates, and 2.) the satiation point of CLB when GPA populations were very high. In addition, interplanting tobacco with clover increased the number of syrphid fly larvae on tobacco. Likewise, tobacco interplanted with sunflowers had increased big-eyed bug, populations, and tobacco-alfalfa and tobacco-tobacco plots had higher stilt bug populations on tobacco. / Master of Science

Graduation date: 1995

La recherche de solutions alternatives à l’usage de pesticides en production horticole est devenue une exigence de santé publique. Ainsi, l’introduction de plantes de service (PdS) est une méthode écologique qui peut contribuer à diminuer le recours à la lutte chimique contre Myzus persicae, le puceron vert du pêcher. L’intérêt de certaines de ces PdS réside dans leur capacité à perturber l’installation du puceron sur son hôte et/ou à diminuer ses performances grâce à l’émission des composés organiques volatils (COV). Cependant, un obstacle majeur à leur utilisation est que leur efficacité se limite à un périmètre restreint et que leur production olfactive est sensible à de nombreuses variables biotiques et abiotiques. Identifier les plantes les plus performantes, comprendre leur mode d’action et chercher à optimiser leur efficacité est donc une démarche propre à favoriser leur emploi en horticulture. L’analyse de l’environnement olfactif est une clé pour évaluer et comprendre les interactions PdS-plante hôte-puceron.Au laboratoire, un typage avec un olfactomètre en Y a permis de sélectionner deux PdS émettrices de mélanges de COV ayant un effet répulsif marqué sur M. persicae : le basilic (Ocimum basilicum) qui agit directement sur l’insecte, et l’œillet d’Inde (Tagetes patula) qui agit indirectement via la plante hôte. Ainsi, les COV émis par T. patula rendent la plante-hôte (le poivron, Capsicum annuum) répulsive. En effet, lors des tests de choix, les pucerons s’orientent vers les poivrons seuls mais évitent les COV émis par des poivrons précédemment mis en culture associée pendant 5 jours avec l’œillet d’inde. Deux composés, le (E)-β-farnésène (EBF) et l'eugénol ont de fortes propriétés répulsives envers M. persicae.Différents facteurs peuvent affecter l’efficacité répulsive de ces plantes (climat, conduite, génétique). Nous avons comparé les COV émis selon les espèces et les chémotypes et testé l’effet répulsif individuel des COV. Cet effet « génotype » a été examiné en étudiant le comportement olfactif de M. persicae en présence des COV individuels émis par différents clones de Romarin (Rosmarinus officinalis). Cinq composés sont répulsifs, l’acétate de bornyle, le camphre, l’α-terpinéol, le terpinène-4-ol et le géranyle acétone. Seul le clone de romarin Voltz Splindler s’est avéré répulsif, alors que les autres clones contiennent également ces 5 composés répulsifs mais dans des proportions différentes. On peut donc conclure que la présence de ces composés ne suffit pas à induire une perturbation du comportement olfactif du puceron et que la concentration, la proportion, voire l’association des COV présents dans les bouquets olfactifs libérés, sont à l’origine de ces résultats contrastés. Par la technique d’électropénétrographie (EPG), nous avons mis en évidence un deuxième effet des COV émis par O. basilicum au stade végétatif et par T. patula au stade floraison sur le puceron. Ils perturbent fortement son comportement alimentaire, en réduisant notamment la durée d’ingestion du phloème qui se traduit par une baisse des ressources nutritionnelles et aboutit à une diminution de sa fécondité. Un suivi de la fécondité sur organe détaché nous a permis de mettre en évidence l’importance du stade phénologique de la PdS sur la composition et l’efficacité du mélange olfactif libéré. Une dernière étape de mon travail a permis de confirmer dans des conditions de cultures sous tunnels, l’effet de COV émis par ces deux PdS sur la démographie de M. persicae liée à une baisse de sa fécondité.En conclusion, cette thèse a mis en évidence que les COV émis dans l’environnement d’une plante hôte par des plantes voisines peuvent fournir un service aux cultures en réduisant les performances de ravageurs tels que M. persicae. Nous avons montré que des variables comme le chémotype ou le stade phénologique de la PdS peuvent modifier son message olfactif et constituer un moyen d’optimiser ce service. / The search for alternatives to the use of pesticides in horticultural production has become a public health requirement. Thus, the introduction of Companion plants (CP) is an ecological method that can help reduce the use of chemical control against Myzus persicae, the green peach aphid. The interest of some of these CP lies in their ability to disturb the installation of the aphid on its host plant and/or to reduce its performance through the emission of volatile organic compounds (VOCs). However, a major obstacle to their use is that their effectiveness is limited to a limited scope and their olfactory production is sensitive to many biotic and abiotic variables. Identifying the most efficient plants, understanding their mode of action and seeking to optimize their effectiveness is therefore an appropriate approach to promote their use in horticulture. Olfactory environment analysis is a key to assessing and understanding CP-host plant -aphid interactions.In the laboratory, we selected with a Y-olfactometer two CP producing VOC mixtures with a marked repellent effect on M. persicae: basil (Ocimum basilicum) which acts directly on the insect, and french marigold (Tagetes patula) which acts indirectly via the host plant. Thus, the VOCs emitted by T. patula make the host plant (pepper, Capsicum annuum) repellent: during the choice tests, the aphids move towards the peppers alone but avoid the VOCs emitted by peppers previously grown intercropped for 5 days with the french marigold. Two compounds, (E)-β-farnesene (EBF) and eugenol have strong repellent properties against M. persicae.Different factors can affect the repellent effectiveness of these plants (climate, plant management, genetics). We compared the VOCs emitted by species and chemotypes and tested the individual repellent effect of VOCs. This "genotype" effect was examined by studying the olfactory behaviour of M. persicae in the presence of individual VOCs emitted by different clones of Rosemary (Rosmarinus officinalis). Five compounds are repellent, bornyl acetate, camphor, α-terpineol, terpinene-4-ol and geranyl acetone. Only the rosemary clone Voltz Splindler was found to be repellent, while the other clones also contain these 5 repellent compounds in varying proportions. It can therefore be concluded that the presence of these compounds is not sufficient to induce a disturbance of the aphid's olfactory behaviour and that the concentration, proportion or even association of VOCs present in the released olfactory bouquets are at the origin of these contrasting results. By the electropenetrography (EPG) technique, we have demonstrated a second effect of the VOCs emitted by O. basilicum in the vegetative stage and by T. patula in the flowering stage on the aphid. They strongly disrupt its feeding behaviour, in particular by reducing the duration of phloem ingestion, which results in a decrease in nutritional resources and leads to a decrease in its fertility. A fertility monitoring on detached organs has allowed us to highlight the importance of the phenological stage of the CP on the composition and efficacy of the olfactory mixture released. A final step in my work confirmed, under tunnel conditions, the effect of VOCs emitted by these two CP on the demographics of M. persicae due to a decrease in its fertility. In conclusion, this thesis highlighted that VOCs emitted into the environment of a host plant by neighbouring plants can provide a service to crops by reducing the performance of pests such as M. persicae. We have shown that variables such as chemotype or phenological stage of the CP can modify its olfactory message and provide a way to optimize this service. We have thus identified disruptive CP and VOCs repellent to M. persicae, the first step towards the development of the push component of a stimulodissuasive diversion strategy to reduce the use of synthetic pesticides against M. persicae.

Made available in DSpace on 2015-03-26T13:30:45Z (GMT). No. of bitstreams: 1 texto completo.pdf: 850834 bytes, checksum: bd6553275d3a6a074c8150b38ec44f71 (MD5) Previous issue date: 2013-02-28 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The broad mite Polyphagotarsonemus latus (Banks, 1904) (Acari: Tarsonemidae), the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) and the green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) are polyphagous and cosmopolitan crop pests which are of great importance for causing serious damage to several crops. In conventional systems, control of such pests has been made by using synthetic acaricides and insecticides. However, using solely agrochemicals may not offer a proper control, and it may sort resistant individuals, besides causing inconveniences to the environment and man health. The use of alternative products instead of agrochemicals for pest control has been increasing, notably due to the increased organic production. Aiming to minimize the effects caused by agrochemicals, plant extracts are being used as an alternative to food production. Vegetable extracts are more compatible with the other management practices, in addition to allow the survivor and better performance of natural enemies. Therefore, here we evaluated the toxicity of chili pepper seeds (Capsicum frutescens L.), corianderseeds (Coriandrum sativum) and marigold extracts (Calendula officinalis L.), chosen among six plant species, after preliminary tests of sub-lethal effects, on the broad mite, on the two-spotted spider mite, on the green peach aphid and on the generalist predator, Chrysoperla externa. Initially, laboratory experiments were performed to assess the lethal and sub-lethal effects of the three extracts on those arthropods. After that, we evaluated, in greenhouse, the efficiency of the vegetable extracts to control the population growth of the herbivorous. The information achieved in these assessments was divided in two chapters. On chapter 1, we evaluated the toxicity of the vegetable extracts on the broad mite and on the two-spotted spider mite. On chapter 2, we assessed the toxicity of the vegetable extracts on the green peach aphid and on its predator, C. externa. In the laboratory, the chili peper and coriander seed hydroalcoholicextracts, in concentration higher than 10 mg/mL, decreased the instantaneous population growth rate of the broad mite, lead to repellency of the adults and caused no-preference for oviposition on substrates treated with the extracts. The marigold extract did not decreased the instantaneous population growth rate of the broad mite, but it caused repellency of the adults and no-preference for oviposition on the substrate treated with the extract, except for the concentration of 50 mg/mL. As for the two-spotted spider mite, all the extracts caused decrease in the instantaneous population growth rate, without, however, achieving the population stability. In greenhouse, the chili pepper and coriander hydroalcoholic extracts, in a concentration of 100 mg/mL and marigold extract in a concentration of 50 mg/mL did not extinguish the populations of broad mite and two-spotted spider mites. Nevertheless, population growth of the broad mite was lower in plants sprayed with marigold extract; for the two spotted spider mite population, growth was lower in plants sprayed with coriander seed extract. All extracts, in all tested concentrations, showed repellency for the green peach aphid. In the evaluation of instantaneous population growth rate of the green peach aphid, only the chili pepper extract induced population decrease. In the greenhouse, none extract reduced the green peach aphid population, nevertheless, the coriander extract retarded its growth. Hydroalcoholic extracts of chili pepper seeds, coriander seed and marigold in the concentration of 10 mg/mL were selective for the predator C. externa. In general, the chili pepper, coriander and marigold hydroalcoholic extracts are promising for the control of the arthropods studied here, however, it is necessary to test higher concentrations to reduce broad mite, two-spotted spider mite and green peach aphid populations. New essays testing the concentrations that stops population growth need to be carried out, as well as the assessment of the selectivity of such concentrations for the predator C. externa. / O ácaro-branco, Polyphagotarsonemus latus (Banks, 1904) (Acari: Tarsonemidae), o ácaro‑rajado, Tetranychus urticae Koch (Acari: Tetranychidae), e o pulgão-verde, Myzus persicae (Sulzer) (Hemiptera: Aphididae), são pragas polífagas, cosmopolitas e de grande importância por causarem sérios prejuízos à produção agrícola. Nos cultivos convencionais, o controle destas pragas tem sido feito com o uso de acaricidas e inseticidas sintéticos. No entanto, o uso exclusivo de agrotóxicos pode não oferecer um controle satisfatório, selecionando indivíduos resistentes e causando inconvenientes ambientais e ao homem. O uso de produtos alternativos em substituição aos agrotóxicos para o controle de pragas tem se acentuado especialmente em decorrência do crescimento da produção orgânica no país. Visando à minimização dos efeitos provocados pelos agrotóxicos, o uso de extratos de plantas se apresenta como alternativa na produção de alimentos. Extratos vegetais são mais compatíveis com as demais práticas de manejo, além de permitirem a sobrevivência e o maior desempenho dos inimigos naturais. Diante disso, neste trabalho, avaliou-se a toxicidade dos extratos de pimenta malagueta (Capsicum frutescens L.), coentro (Coriandrum sativum) e calêndula (Calendula officinalis L.), escolhidos entre seis plantas, após testes preliminares de efeitos sub-letais, sobre o ácaro-branco, ácarorajado, pulgão-verde e o predador generalista Chrysoperla externa. Inicialmente, realizaram-se experimentos em laboratório para verificar os efeitos letais e sub-letais dos extratos acima citados sobre os artrópodes. Posteriormente, avaliou-se, em casa de vegetação, a eficiência de cada extrato vegetal no controle do crescimento populacional do ácaro-branco, ácaro-rajado e pulgão-verde. As informações obtidas foram divididas em dois capítulos. No capítulo 1, avaliou-se a toxicidade dos extratos vegetais sobre o ácaro-branco e o ácaro-rajado. No capítulo 2, avaliou-se a toxicidade dos extratos vegetais sobre o pulgão-verde e seu predador C. externa. Em laboratório, verificou-se que os extratos hidroalcoólicos de sementes de pimenta malagueta e de coentro, em concentração maior que 10 mg/mL, reduziram a taxa instantânea de crescimento populacional do ácaro-branco, provocaram a repelência dos adultos e causaram a não preferência de oviposição em substratos tratados com os extratos. O extrato de calêndula não reduziu a taxa instantânea de crescimento populacional do ácaro-branco, mas causou repelência aos adultos e não preferência de oviposição nos substratos tratados com o extrato, exceto na concentração de 50 mg/mL. Já, para o ácaro-rajado, todos os extratos causaram repelência e decréscimo da taxa instantânea de crescimento sem, no entanto, atingir a estabilidade populacional. Em casa de vegetação, os extratos hidroalcoólicos de pimenta malagueta e coentro na concentração de 100 mg/mL e calêndula, a uma concentração de 50 mg/mL, não extinguiram a população do ácaro-rajado e do ácaro-branco. Contudo, o crescimento populacional do ácaro-branco foi menor nas plantas pulverizadas com o extrato de calêndula e do ácaro-rajado, nas plantas pulverizadas com extrato de coentro. Todos os extratos, em todas as concentrações, mostraram repelência ao pulgão-verde. Na avaliação da taxa instantânea de crescimento populacional do pulgão, o único extrato que causou declínio da população foi o de pimenta malagueta. Em casa de vegetação, nenhum extrato reduziu a população do pulgão, porém o extrato de coentro retardou o crescimento do pulgão-verde. Extratos hidroalcoólicos de pimenta, coentro e calêndula na concentração de 10 mg/mL foram seletivos ao predador C. externa. Em geral, os extratos hidroalcoólicos de pimenta malagueta, coentro e calêndula são promissores no controle dos artrópodes estudados, no entanto é necessário testar concentrações maiores para reduzir a população do ácaro-branco, ácaro-rajado e pulgão. Novos experimentos com concentrações que cause a paralização do crescimento populacional desses artrópodes devem ser conduzidos com possibilidade de obter redução populacional dos ácaros, do afídeo e para a avaliação da seletividade ao predador C. externa.