No description available.

No description available.

During post-alighting behaviour gravid female turnip root fly, D.jloralis, select a plant for oviposition predominantly during the initial landing phase; the cabbage root fly, D.radicum, also utilise the leaf resting phase. The post-alighting behaviour exhibited by D.radicum and D.floralis infers that oviposition site selection is primarily based upon positive stimuli present on the leaf surface. Ranking of four genotypes of plants for antixenotic resistance to oviposition by D.radicum and D.jloralis was found to be the same for both fly species, tested in the laboratory (swede cv Doon Major, most susceptible; kale cv Fribor, most resistant) and varied x80 (D.floralis) and x5 (D.radicum). Field experiments showed that oviposition (which was dominated by D.radicum) varied x2 between plant genotypes (swede cv Doon Major, most susceptible; swede cv GRL aga, most resistant). Testing of Brassica leaf surface extracts, applied to surrogate plants, indicated that leaf surface chemicals strongly influence the site of oviposition of D.floralis. Methanol soluble polar compounds are the most stimulatory element for D.floralis and a fraction which contained aliphatic glucosinolates stimulated oviposition strongly although glucosinolates were not the primary oviposition stimulant. Collaborative experiments indicate that "CIF" (cabbage identification factor) is probably present in this fraction. The concentrations of Brassica root sugars are generally reduced by the damage of both D.radicum and D.floralis and appear to influence larval development. The percentages of plant fibre and lignin in the roots of Brassicas rise following the damage of D.floralis. The concentrations of individual glucosinolates in Brassica roots arc radically altered by the damage of D.floralis and D.radicum. D.floralis damage resulted in a rise in the concentration of aromatic glucosinolates and a fall in the concentration of aliphatic glucosinolates. D.radicum damage generally resulted in an elevated concentration of both aliphatic and aromatic glucosinolates. There was no clear evidence that glucosinolatc profiles were associated with different levels of antibiotic resistance to D.radicum and D.floralis. GRL aga (SCRI breeding line) was consistently resistant to the oviposition and larval feeding of D.radicum and D.floralis both in the laboratory and in the field. It was shown that the use of end-of-season chemical analysis to assess the influence of plant chemistry on insect development or host plant resistance in field experiments and the use of damage indexes based on the percentage of a plant root damaged by D.radicum may be flawed.

Delia radicum L. (Diptera: Anthomyiidae), the cabbage root fly, is a specialist root-feeding insect pest of Brassica crops. The impending withdrawal of chlorpyrifos, one of the main pesticides used against D. radicum, opens new opportunities to research alternative pest management strategies. Manipulating host plant location cues to influence D. radicum adult and larval behaviour, along with induced plant defence responses, offer potential integrative crop protection solutions (Chapter 1). This thesis aimed to identify the semiochemistry underpinning D. radicum larval host plant location, and to investigate whether plant defence induction treatments (methyl jasmonate [MeJA], D-Fructose) and a herbivore induced volatile (dimethyl disulfide [DMDS]) affect D. radicum larval performance and adult oviposition preference. In choice-test bioassays, larvae were inconsistent in their responses to root exudates collected from Brassica host plants (Chapter 2). A combined bioassay and EthoVision® video-tracking approach was developed to record and analyse larval movements in response to volatiles emitted from host and non-host plant roots (Chapter 3). Larvae were significantly attracted to host plant root volatiles. Olfactory stimuli from roots of the non-host plant onion (Allium cepa L. ‘Ailsa Craig’), which share overlapping, yet distinctive volatile profiles to that of Brassica plants, also elicited positive taxis. By analysing the volatile metabolome of broccoli (B. oleracea L. convar. botrytis L. Alef. var. cymosa Duchesne ‘Parthenon’) and onion roots using solid phase micro extraction-gas chromatography-mass spectrometry (SPME-GCMS), a suite of candidate volatile orientation cues were identified. A SPME-based method was developed to non-invasively collect root volatiles in situ from glasshouse- and field-grown broccoli plants pre- and post-D. radicum infestation (Chapters 4, 5 and 6). GC-MS analyses revealed that sulfur compounds, showing characteristic temporal emission patterns, were the principal volatiles released by roots in response to damage. This new method, which has potential for wide application in chemical ecology research, allows the study of volatiles in the soil in situ that are critical for interactions between trophic levels. In EthoVision® bioassays, a major volatile constituent of broccoli roots, DMDS, was attractive to larvae, but toxic at the highest dose tested (Chapter 3). Glasshouse and on-farm experiments using broccoli were conducted to evaluate the efficacy of MeJA, D-Fructose and DMDS against D. radicum compared to commercially available crop protection products (chlorpyrifos [Dursban® WG], spinosad [Tracer®], Steinernema feltiae Filipjev [Nematoda: Steinernematidae] [Entonem] and garlic granules [ECOguard®]). MeJA and garlic reduced larval performance under glasshouse conditions whereas D-Fructose and DMDS did not at the concentrations tested (Chapter 7). In field studies, MeJA combined with reduced rate chlorpyrifos, spinosad, and S. feltiae all showed partial efficacy for controlling D. radicum larvae. Inherent field site, weather and D. radicum population density variability highlighted that glasshouse results cannot always be reproduced in more complex field environments (Chapter 8). Further research is needed into formulation, mode of application and timing to improve efficacy of promising treatments that may help in future integrated pest management (IPM) for this key pest in the absence of existing pesticides.

No description available.

Intercropping systems offer potential benefits relative to monocultures of increased crop yields and improved pest control through physical, chemical, or behavioural interference and the enhancement of natural enemy populations, prompting increased predation and parasitism. Intercrops of canola (Brassica napus L.) and wheat (Triticum aestivum L.) in various proportions were investigated at three sites in Alberta, Canada, in 2005 and 2006, to determine effects on 1) agronomic parameters, including crop grain and biomass yields, crop quality (canola oil and canola and wheat protein), lodging, soil microbial communities, and wheat leaf diseases; 2) pest insects, including flea beetle (Phyllotreta spp.) (Coleoptera: Chrysomelidae) damage to seedling canola and root maggot (Delia spp.) (Diptera: Anthomyiidae) adult collection numbers, egg populations, and canola taproot damage; and 3) beneficial insects, including ground beetles (Coleoptera: Carabidae) and the predator-parasitoid Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae). Crop yields were similar in intercrops and monocultures, and benefits of intercropping were observed in enhanced crop quality characteristics in some site-years. Neither soil microorganisms nor wheat leaf diseases generally responded to intercropping regimes. Intercropping did not reduce flea beetle damage to canola seedlings. Flea beetle damage was greatest at the first true-leaf stage of canola development. Although a thiamethoxam seed treatment reduced flea beetle herbivory, untreated plots generally did not sustain greater than 20% damage, suggesting that seed treatments were usually unnecessary. Adult Delia did not respond to intercropping canola with wheat, but egg populations were lower in intercrops on a land area basis. Canola taproot damage was as much as 13% reduced in intercrops compared to monocultures. Carabid beetles appeared to respond to qualities of the intercrops and monocultures, such as ground cover, rather than to the level of vegetational diversity itself, but carabid diversity was enhanced in diverse intercrops compared to canola monocultures in one site-year. Aleochara bilineata adult populations and parasitism rates were favoured in canola monocultures, but a temporal shift in A. bilineata adult collection numbers suggests reduced preference for canola monocultures in early summer. Benefits of canola-wheat intercrops identified in this study do not appear sufficient to recommend these cropping systems for widespread adoption in western Canada. / Plant Science

Les symbiotes d'insectes peuvent considérablement influencer leurs hôtes de diverses manières. Nous avons étudié ici la communauté de microbes de la mouche du chou (Delia radicum) et plus particulièrement le rôle de son microbiote intestinal et de Wolbachia, une bactérie intracellulaire. La transmission verticale et maternelle de Wolbachia était de 100% et nous n’avons trouvé aucune preuve de manipulation de la reproduction telles que l’incompatibilité cytoplasmique, la parthénogenèse thélytoque, la féminisation ou la dégénérescence des embryons mâles. Les effets de Wolbachia sur D. radicum étaient significatifs mais modérés, et se compensaient mutuellement (réduction du taux d’éclosion, meilleure survie larvo-nymphale, temps de développement plus long et augmentation de la mortalité des femelles en conditions de stress), ce qui suggère une infection quasi neutre chez cette espèce, même si nous avons observé une augmentation de la fréquence d’infection en conditions idéales. L'influence du microbiote intestinal a été étudiée en utilisant un antibiotique, la tétracycline, avec un protocole sur trois générations, ce qui a permis de discerner l’effet direct (toxique) de la tétracycline de ses effets indirects (perte de symbiotes) sur l’hôte. Le traitement antibiotique de D. radicum a eu de multiples effets, généralement négatifs, sur les traits d’histoire de vie des descendants, ces effets pouvant être détectés jusqu'à deux générations après le traitement. La perturbation du microbiote intestinal semble avoir un rôle plus important qu'un simple effet toxique de la tétracycline elle-même. De plus, l’étude suggère que le microbiote semble avoir un rôle bénéfique chez cette espèce, et qu’il est au moins partiellement hérité de la mère. Pour finir, nous avons étudié si Wolbachia pouvait modifier le dialogue plante-insecte entre D. radicum et l’une de ses plantes-hôtes, le colza (Brassica napus). La présence du symbiote a diminué les concentrations de glucosinolates dans les feuilles, ce qui suggère que Wolbachia pourrait améliorer la fitness de son hôte en diminuant les signaux chimiques de la plante pouvant être utilisés par les conspécifiques et/ou ennemis naturels de D. radicum. Cette étude a montré le potentiel d'une bactérie intracellulaire à influencer les relations plantes-insectes et a permis de discuter des interactions tri-trophiques entre les symbiotes, leurs insectes-hôtes et un troisième niveau trophique : la plante. Cette thèse démontre qu'il est maintenant nécessaire de prendre en compte les symbiotes dans de prochaines études, afin de mieux comprendre les relations possibles entre différents partenaires, ainsi que leurs implications écologiques ou évolutives. / Microbial symbionts can deeply influence their animal hosts in various ways. Here, we studied the community of microbes of the cabbage root fly (Delia radicum) and more precisely the role of its gut microbiota and of Wolbachia, an intracellular bacterium. The vertical maternal transmission of Wolbachia was perfect, and we found no evidence of manipulation of reproduction such as cytoplasmic incompatibility, thelytokous parthenogenesis, feminization nor male killing. Wolbachia infection had significant but moderate and mutually compensating effects on D. radicum (reduced hatch rate, improved larvo-nymphal viability, longer development time and increased female mortality in stress conditions), suggesting that infection might be nearly neutral in this strain, although we observed an increase in infection frequency in ideal rearing conditions. The influence of the gut microbiota was studied using an antibiotic, tetracycline, with a protocol spanning three generations, which allowed to discriminate the possible direct (toxic) effect of tetracycline from its indirect effects (due to the loss of gut symbionts). Antibiotic treatment of adults led to multiple and mostly negative effects on life history traits of their offspring and grandchildren. Data suggested a larger role of gut microbiota perturbation than of a toxic effect, that the microbiota was partially inherited maternally, and that the “wild-type” gut microbiota was beneficial in this species. Finally, we investigated whether Wolbachia could modify the insect-plant dialogue between D. radicum larvae feeding on roots of oilseed rape (Brassica napus). The presence of the symbiont decreased glucosinolate concentrations in the leaves, suggesting that Wolbachia could increase the fitness of its host by decreasing plant cues used by D. radicum conspecifics and/or natural enemies. This study showed the potential of an intracellular bacteria to influence plant-insect relationships, and allowed to discuss the tri-trophic interactions between symbionts, their insect hosts and a third trophic level: the plant. This thesis demonstrates the necessity to consider intracellular and extracellular symbionts in further studies, in order to unravel all the possible relationships between different partners, as well as their ecological or evolutionary implications.

Au sein des écosystèmes, les Composés Organiques Volatils (COVs) émis par les plantes jouent un rôle majeur dans les interactions trophiques. Ces signaux olfactifs vont renseigner les insectes phytophages sur la présence de leurs hôtes mais permettent aussi de recruter les ennemis naturels. Il a été montré que certains de ces composés pouvaient être utilisés pour manipuler le comportement des insectes phytophages s’attaquant aux cultures. La stratégie push-pull, vise à combiner des stimuli positifs et négatifs pour un insecte ravageur afin de le repousser d’une culture tout en l’attirant sur une plante piège implantée en périphérie du champ où il pourra être contrôlé. L’objectif de cette thèse est d’améliorer notre compréhension et nos connaissances sur la manipulation de la communication chimique entre les plantes et les insectes phytophages à l’aide de COVs de synthèse et de préférence d’hôte afin de mettre en place sur le terrain une stratégie de type push-pull pour protéger une culture de la mouche du chou (Delia radicum). Dans un premier chapitre, nous montrons que dans un système push-pull composé (i) de diffuseur de diméthyldisulfure DMDS (composante push) et (ii) d’une bordure de choux chinois supplémenté avec de l’acétate d’hexenyl (Z-3-HAC) (composante pull), il est possible de modifier fortement le comportement d’oviposition de D. radicum sans impacter de façon négative ses principaux ennemis naturels. Les limites agronomiques et d’utilisation du DMDS atteintes, nous avons recherché d’autres COVs ayant un effet répulsif. Lors d’une seconde expérimentation en push-pull, l’eucalyptol (1-8 cinéol) à permis de réduire le nombre de pupes de D. radicum retrouvées aux pieds des plants de brocoli de 60%. Suite à ce résultat encourageant, nous avons qualifié au laboratoire l’effet inhibiteur de ce monoterpène sur l’oviposition de la mouche du chou et en avons conclu qu’il permet de masquer le bouquet de COVs attractif d’un hôte. L’efficacité de la composante push étant fortement liée à la diffusion des COVs, nous avons ensuite testé au laboratoire et sur le terrain un nouveau type de diffuseur à base de cires végétales, permettant d’émettre l’eucalyptol de manière passive mais régulière pendant plusieurs semaines. L’étude réalisée montre le fort potentiel du diffuseur qui est à la fois bon marché, facile d’utilisation et fiable en terme de diffusion, permettant ainsi d’envisager son utilisation dans des stratégies de lutte intégrée à grande échelle. Parallèlement à l’étude de la composante push, nous avons cherché à améliorer l’efficacité de la composante pull. Le chou chinois (Brassica rapa) permet grâce à sa forte attractivité de capter et détourner la pression de phytophagie de la culture d’intérêt. Nous montrons qu’au sein de sa grande diversité, certaines variétés comme Richi (appartenant à la sous espèce pekinensis) sont préférentiellement attaqué par la mouche du chou, ce qui en fait de bons candidats au développement d’une composante pull efficace. A la lumière de la bibliographie et de nos résultats, nous proposons une réflexion générale sur le système étudié. Ainsi, nous concluons que, au moins dans le cas de la mouche du chou, les COVs ne peuvent probablement pas être les seuls outils considérés dans le développement d’une stratégie push-pull. / Within ecosystems, Volatile Organic Compounds (VOCs) emitted by plants play a major role in trophic interactions. These olfactive signals will inform phytophagous insects about the presence of their hosts, but they also allow to recruit their natural enemies. It has been shown that some of these compounds could be used to manipulate the behaviour of insect crop pests. The push-pull strategy aims at combining positive and negative stimuli to push a pest out of a crop and lure it into a trap crop located in the periphery of the field, where it can be controlled. The objective of this thesis is to improve our understanding and our knowledge on the manipulation of chemical communication between plants and phytophagous insects, using synthetic VOCs and host preference as tools, to protect a crop against the cabbage root fly (Delia radicum). In a first chapter, we show that in a push-pull made of (i) DMDS dispensers as a push component and (ii) chinese cabbage strips supplemented with hexényl acetate (Z-3-HAC) as a pull component, it is possible to strongly reduce oviposition behaviour in D. radicum without impacting its natural enemies. Agronomic limits to the use of DMDS led us to search for other repulsive VOCs. In a second push-pull field experiment, using eucalyptol (1-8 cinéol), reduced by 60% the number of D. radicum pupae produced in the crop. This encouraging result led us to characterize the inhibition effect of this monoterpene in the lab and concluded that it allows to mask the attractive blend of VOCs released by the host. The efficiency of the push component being strongly linked to that of the VOC diffusion, we have then tested both in the laboratory and in the field a new kind of dispenser made of vegetal waxes, allowing to diffuse eucalyptol passively but regularly during several weeks. This study shows the good potential of this device, which is affordable, easy to use and reliable in terms of diffusion, in integrated pest management strategies at a large scale. In parallel of our studies on the push component, we have also sought to increase the efficiency of the pull component. Thanks to its strong attractivity toward D. radicum, Chinese cabbage (Brassica rapa), allows to divert pest pressure from the cash crop. We show that within its important genetic diversity, some cultivars such as Richi (of the pekinensis subspecies) are preferentially attacked by D. radicum, which makes them good candidates to develop an efficient pull component. Using both the literature and our own results, we finally propose a general discussion on the system studied. We conclude that, at least in the case of the cabbage root fly, VOCs are probably not the sole tools to consider when trying to develop a push-pull strategy.

Les recherches menées au cours des dernières années ont permis de mettre en évidence les nombreuses fonctions écologiques des composés organiques volatils (COVs) émis par les plantes. Cette thèse a eu pour objectif d'utiliser ces connaissances dans un cadre de protection des cultures. Nous avons essayé de poser les bases d'une stratégie de type « Push-Pull » contre la mouche du chou (Delia radicum) en utilisant des sources d'odeurs synthétiques (diffuseurs de COVs) ou des sources d'odeurs naturelles (plantes compagnes). A partir d'observations menées en plein champ nous avons sélectionné plusieurs brassicacées présentant des taux d'infestations contrastés vis-à-vis de la mouche du chou. Des expérimentations de laboratoires combinant des études comportementales et des analyses chromatographiques ont permis (i) d'établir un lien entre l'infestation et l'attractivité de certaines plantes (ii) d'identifier de nouveaux COVs potentiellement impliqués dans les prises de décisions comportementales de D. radicum. En parallèle, des études de terrain ont permis de tester l'efficacité de diffuseurs de COVs synthétiques au sein de parcelles expérimentales, que ce soit (i) pour favoriser le recrutement d'ennemis naturels (ii) attirer (composante « Pull ») ou repousser (composante « Push ») la mouche du chou. Enfin, l'utilisation de plantes pièges concentrant le ravageur semble être intéressante pour modifier la répartition de la mouche du chou à l'échelle de la parcelle en vue de protéger des cultures d'intérêt telles que le brocoli. / Volatile organic compounds (VOCs) emitted by plants are used by phytophagous, predatory and parasitoid insects to adjust behavioral decisions in complex environments. We aimed at using these ecological functions of VOCs in crop protection. We developed the first steps of a "Push-Pull" strategy toward the cabbage root fly (Delia radicum) with both dispensers of synthetic VOCs and natural blends of VOCs released by plants. We conducted a field study to select brassicaceous plants exhibiting contrasted levels of infestation toward the cabbage root fly. Laboratory bioassays combining behavioral observations and gas chromatographic analyses allowed to (i) investigate the relation between plant infestation and plant attractiveness (ii) identify novel VOCs involved in behavioral decisions of the cabbage root fly. Parallel field experiments were used to test the potential of dispensers of synthetic VOCs to (i) enhance natural enemies recruitment (ii) modify cabbage root fly behavior, attracting ("Pull" component) or repelling the pest ("Push" component). Finally, we demonstrated that attractive plants are promising for a trap crop approach enabling to redistribute cabbage root fly density at the field scale in order to protect main crop such as broccoli.

The female protagonist Catherine Danielle Clark (Kya) in Delia Owens’ Where the Crawdads Sing is abandoned by her family at a young age and grows up alone in a marshland environment in 1950s North Carolina. Shunned by the local community, Kya relies on nature to help her survive and to teach her about life and love—until one day she finds herself accused of murder. The purpose of this essay is to examine how the author uses nature and the protagonist Kya in order to promote environmental consciousness in the novel, interlinking them in ways that advance identifiable environmental concepts. Therefore, the essay carries out a close reading of the text using three different ecocritical lenses—postcolonial ecocriticism, ecofeminism, and climate change criticism—and with a focus on three themes, respectively—voice, agency, and urgency. It finds first, through an exploration of voice and a postcolonial ecocritical lens, that both nature and Kya are othered in the novel but come to be heard and respected over time; second, through an exploration of agency and an ecofeminist lens, that activity rather than passivity is ascribed to nature and Kya, and their interconnectedness acts as a positive force for change; and third, through an exploration of urgency and a climate change criticism lens, that the interconnectedness of nature and Kya persuades readers to care about the natural world and appreciate the need to respect and protect it, using a subtle rather than overtly political message. Overall, Delia Owens’ use of nature and the protagonist promotes three key environmental concepts: the voice of nature, the agency of nature, and the urgency of respecting nature. This essay concludes that Where the Crawdads Sing speaks to the environmental consciousness of readers in these times of troubling climatic change, lending itself to a variety of ecocritical readings and offering a glimmer of hope. / Den kvinnliga huvudpersonen Catherine Danielle Clark (Kya) i Delia Owens Where the Crawdads Sing överges av sin familj i ung ålder och växer upp ensam i en våtmarksmiljö i 1950-talets North Carolina. Kya är utstött av lokalsamhället och förlitar sig på naturen för att hjälpa henne att överleva och för att lära henne om liv och kärlek—tills hon en dag finner sig anklagad för mord. Syftet med denna uppsats är att undersöka hur författaren använder naturen och huvudpersonen Kya för att främja miljömedvetenhet i romanen och koppla samman dem på sätt som främjar identifierbara miljökoncept. Därför utförs en närläsning av texten med tre olika ekokritiska linser—postkolonial ekokritik, ekofeminism och klimatkritik—och med fokus på tre respektive teman—röst, agens och brådska. Den konstaterar först, genom ett utforskande av röst och en postkolonial ekokritisk lins, att både naturen och Kya är sedda som ”den andre” i romanen men kommer att höras och respekteras med tiden; för det andra, genom ett utforskande av agens och en ekofeministisk lins, att aktivitet snarare än passivitet tillskrivs naturen och Kya, och deras sammankoppling fungerar som en positiv kraft för förändring; och för det tredje, genom ett utforskande av brådska och en klimatkritik lins, att sammankopplingen av naturen och Kya övertalar läsarna att bry sig om den naturliga världen och uppskatta behovet av att respektera och skydda den, med hjälp av ett subtilt snarare än öppet politiskt budskap. Sammantaget främjar Delia Owens användning av naturen och huvudpersonen tre viktiga miljöbegrepp: naturens röst, naturens agens och brådskan att respektera naturen. Denna uppsats drar slutsatsen att Where the Crawdads Sing talar till läsarnas miljömedvetenhet i dessa tider av oroande klimatförändringar, lämpar sig för ett antal olika ekokritiska läsningar och erbjuder en strimma av hopp.