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A novel strategy to control the fall armyworm with entomopathogenic nematodes
Get PDFThesis committee:
Prof. Ted Turlings, Thesis director, University of Neuchâtel, Neuchâtel, CH
Dr. Stefan Toepfer, Co-supervisor, CABI, Delémont, CH
Prof. Pilar Junier, Internal expert, University of Neuchâtel, Neuchâtel, CH
Dr. Ivan Hiltpold, External expert, Agroscope, Changins, CH
September 2023
No de thèse : 3070La chenille légionnaire d'automne (Spodoptera frugiperda, Smith ; Lepidoptera : Noctuidae) est une espèce d'insecte originaire des Amériques connue pour être un ravageur agricole majeur. Elle peut se nourrir d'une grande variété de plantes, mais elle est particulièrement dévastatrice pour le maïs. L'invasion récente de la chenille légionnaire d'automne en Afrique et en Asie provoque des ravages considérables dans la culture du maïs, entraînant une augmentation importante de l'utilisation d'insecticides synthétiques nocifs, dont l'efficacité est souvent marginale. Cette efficacité limitée est principalement due au comportement alimentaire spécifique de ces chenilles. Elles se trouvent principalement cachées en profondeur dans les feuilles enroulées du maïs, ce qui en fait des cibles difficiles pour les insecticides de contact conventionnels. En outre, la chenille légionnaire d'automne a rapidement développée des résistances à une large gamme d'insecticides synthétiques ainsi qu'à certaines toxines de Bacillus thuringiensis (Bt) couramment utilisées contre les insectes nuisibles dans certaines régions du monde. Des solutions de lutte efficaces, sûres et durables sont primordiales pour garantir la sécurité alimentaire et préserver les organismes bénéfiques, tels que les pollinisateurs, ainsi que l'environnement.
Plusieurs agents de contrôle biologique, tels que les nématodes entomopathogènes, peuvent être très efficaces contre des chenilles, mais leur application sur les feuilles des plantes est difficile. Les nématodes entomopathogènes sont des parasites qui ciblent spécifiquement les insectes. Ils peuplent les sols du monde entier et sont couramment utilisés comme agents de lutte biologique depuis des décennies, notamment parce qu'ils ont la capacité de localiser activement, d'infecter et de rapidement tuer des insectes. En tant qu'organismes du sol, les nématodes sont particulièrement sensibles aux conditions abiotiques aériennes, et notamment présentes sur le feuillage, telles que la dessiccation et le rayonnement UV. L'objectif de cette thèse est de relever ces défis en explorant de nouvelles solutions pour appliquer et protéger les nématodes entomopathogènes sur les feuilles de maïs, afin d'assurer un contrôle efficace et durable de la chenille légionnaire d'automne.
Nous démontrons dans les chapitres 1 et 2 que des nématodes isolés localement représentent d'excellents candidats contre la chenille légionnaire d'automne. Ils offrent également l'avantage d'éviter le risque d'introduction d'espèces exotiques dans une région cible, associé à l'utilisation de nématodes commerciaux souvent non indigènes. Dans le chapitre 3, nous explorons différentes méthodes de formulation des nématodes pour une application foliaire. Une formulation développée lors ce travail à base de gel de carboxyméthylcellulose s’est avérée très efficace, tuant 100 % des chenilles en laboratoire et réduisant de manière significative l’infestation des plantes lors d'essais préliminaires sur le terrain au Rwanda. Dans le chapitre 4, nous évaluons, au long d'une saison complète de croissance du maïs au Rwanda, l’efficacité de nématodes formulés dans le gel. Les résultats démontrent que, formulés dans le gel, les nématodes ont systématiquement limité les dommages aux plantes. En outre, ce traitement a été nettement plus efficace pour réduire l'infestation des plantes que la cyperméthrine, un insecticide couramment utilisé, et a conduit à une augmentation du rendement par rapport aux plantes contrôles non traitées. Enfin, nous avons démontré au chapitre 5 que l'ajout de substances naturelles et facilement disponibles dans le gel prolongeait la survie et l'efficacité des nématodes exposés aux rayons UV, et ceci à un coût abordable. Cette avancée pourrait se traduire par une efficacité accrue des nématodes dans des conditions agricoles réelles et contribuer à étendre l'utilisation des nématodes contre les ravageurs foliaires.
Cette thèse démontre le potentiel des nématodes entomopathogènes natifs, isolés localement, pour lutter contre la chenille légionnaire d'automne et représente une étape vers la gestion durable de ce ravageur dévastateur.
ABSTRACT
The fall armyworm (Spodoptera frugiperda, Smith; Lepidoptera: Noctuidae) is an insect species native to the Americas known to be a major agricultural pest. It can feed on a large variety of plants, but is particularly devastating to maize. The recent invasion of the fall armyworm in Africa and Asia has wreaked havoc in maize cultivation, leading to a tremendous increase in the use of harmful synthetic insecticides, which are often only marginally effective. This limited efficacy is mainly due to the specific feeding behaviour of the fall armyworm caterpillars, which are mostly found deep within the wrapped leaves of the maize whorl, making them difficult targets for conventional contact insecticides. In addition, the fall armyworm has rapidly developed resistances to a wide range of synthetic insecticides as well as to some Bacillus thuringiensis (Bt) toxins commonly employed against insect pests in some regions of the world. Effective, safe and sustainable control alternatives are desperately needed to ensure food security as well as to preserve beneficial organisms, such as pollinators, and the environment.
Several biological control agents, such as entomopathogenic nematodes, can be quite effective in killing armyworms, but their application on plant leaves is challenging. Entomopathogenic nematodes are parasites that specifically target insects. They live in soils around the world and are commonly used as biological control agents for decades, notably because they have the ability to actively locate, infect and swiftly kill insects. As soil organisms, nematodes are particularly sensitive to the abiotic conditions found aboveground and on foliage, such as desiccation and UV radiation. The aim of this thesis is to address these challenges by exploring novel solutions to apply and protect entomopathogenic nematodes on maize leaves to ensure effective as well as sustainable control of the fall armyworm.
We showed in Chapters 1 and 2 that locally isolated nematodes represent excellent candidates against the fall armyworm. They also offer the advantage of preventing the risk of introducing foreign species in a target country, associated with the use of often non-native commercially available nematodes. In Chapter 3, we explored different methods to formulate nematodes for aboveground application. We found a here-developed carboxymethyl cellulose gel formulation to be quite effective, killing 100% caterpillars in laboratory conditions and significantly reducing FAW infestations in preliminary field trials in Rwanda. In Chapter 4, we showed that throughout a full maize growing season in Rwanda, nematodes formulated in the gel consistently limited plant damage. In addition, the nematode-gel was significantly more effective than the commonly used insecticide cypermethrin in reducing armyworms infestation. This led to an increased grain yield as compared to untreated control plants. Lastly, we demonstrated in Chapter 5 that the addition of affordable, readily available, natural substances to the gel formulation prolonged the survival and effectiveness of nematodes exposed to UV radiation. This could translate into an increased efficacy of the nematode-gel formulation in realistic farming conditions as well as contribute to expanding the use of nematodes against aboveground pests.
This thesis demonstrates the potential of locally isolated entomopathogenic nematodes for fall armyworm control and represents a step towards the sustainable management of this devastating pest
Border Bureaucracies: A Literature Review of Discretion in Migration Control
Get PDFThis literature review summarizes findings from 63 articles published between 2001 and 2020 that study discretion of frontline workers at migration control. The results demonstrate that discretionary practices in various migration control situations (e.g., border zones, migration agencies, courts, public welfare services, and detention centers) are widespread but share common patterns. Frontline workers’ racialized prejudices and perceptions of migrant deservingness were the most dominant patterns found in the data, although there were some disagreements about which were most influential. Discretion of frontline workers was described as foremost detrimental to migrants, as it amplified the migrants’ vulnerable situations, even if it occasionally could increase individual migrants’ room for agency and strategic maneuvering. Contrary to the assumption underpinning the control gap-thesis in immigration policy literature that governments’ capacity to control migration is hampered by the significant discretion at the frontlines, many studies in our sample describe how governments shape the discretionary practices of frontline workers through informal, subtle, and opaque governing strategies. These informal governing strategies enable central governments to deflect responsibility for discriminatory and inhumane policy outcomes
Tool Wear Monitoring Using Multi-sensor Time Series and Machine Learning
Get PDFIn the milling process of micro-machining, the optimization process is one of the keys to reduce production cost. By monitoring the tool wear and detecting when it is no longer acceptable, the machining process can be adjusted more accurately. This research explores four approaches using different machine learning models to predict machining tool wear during the milling process. The study is based on a dataset created with a face milling operation on
stainless steel (AISI 303) round material. The machining is divided into a number of stairs and is performed with a 3mm tungsten carbide. Three different types of sensors are used to measure the wearing process, with acoustic emission, accelerometers and axis currents. The better approach achieved a f1-score of 73% on five classes with a Extra Trees Classifier.tru
Vot’ artic’ est formidab’: une étude multifactorielle de la chute des liquides post-obstruantes finales de mot en français
Get PDFCet article présente une analyse multifactorielle du comportement des consonnes liquides post-obstruantes en position finale de mot en français. Plus précisément, nous nous intéressons au phénomène par lequel un ou final dans la transcription orthographique d’un mot n’est pas prononcé dans la parole continue, p. ex. comme dans les items « découvre » et « terrible », respectivement prononcés [dekuv] et [teʁib] au lieu de [dekuvʁ] et [teʁibl]. Au total, plus de 2500 items comportant un cluster obstruante+liquide en fin de mot ont été extraits d’un corpus de parole d’une durée de 13 heures, qui a été étiqueté à différents niveaux. Ce corpus comprend les productions de 120 locuteurs originaires de 3 pays francophones (Belgique, France et Suisse), enregistrés dans deux tâches différentes (lecture et conversation). Pour déterminer ce qui affecte la (non-)prononciation de ou dans ces contextes, une douzaine de prédicteurs de différentes natures sont testés dans un même modèle statistique. Les caractéristiques phonétiques telles que le lieu et le mode d’articulation, le contexte droit, le statut prosodique et le taux d’articulation; mais aussi les prédicteurs liés aux locuteurs (pays d’origine, sexe, âge, classe sociale) et au style de parole sont pris en compte. Des modèles mixtes linéaires généralisés révèlent que seulement la moitié d’entre eux ressortent comme jouant un rôle significatif sur la variable à l’étude. Les résultats sont discutés à la lumière dʼétudes antérieures portant sur les aspects sociolinguistiques des variantes de prononciation en français.tru
Autour de la Suisse en 30 lieux inattendus
No full textTrente essais écrits par des géographes pour découvrir des lieux typiques de la Suisse, des sous-sols de la chapelle Sainte-Croix à Müstair aux ruelles de la ville de Fribourg, en passant par le cimetière Saint-Martin de Veve
Juvenile vervet monkeys rely on others when responding to danger
No full textAbstractPrimate alarm calls are mainly hardwired but individuals need to adapt their calling behaviours according to the situation. Such learning necessitates recognising locally relevant dangers and may take place via their own experience or by observing others. To investigate monkeys alarm calling behaviour, we carried out a field experiment in which we exposed juvenile vervet monkeys to unfamiliar raptor models in the presence of audiences that differed in experience and reliability. We used audience age as a proxy for experience and relatedness as a proxy for reliability, while quantifying audience reactions to the models. We found a negative correlation between alarm call production and callers’ age. Adults never alarm called, compared to juveniles. We found no overall effect of audience composition and size, with juveniles calling more when with siblings than mothers or unrelated individuals. Finally, concerning audience reactions to the models, we observed juveniles remained silent with vigilant mothers and only alarm called with ignoring mothers, whereas we observed the opposite for siblings: juveniles remained silent with ignoring siblings and called with vigilant siblings. Despite the small sample size, juvenile vervet monkeys, confronted with unfamiliar and potentially dangerous raptors, seem to rely on others to decide whether to alarm call, demonstrating that the choice of the model may play an important key role in the ontogeny of primate alarm call behaviour.
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Hydrogeological modeling of the Roussillon coastal aquifer (France): stochastic inversion and analysis of future stresses
Get PDFAbstractGlobal climate change-induced stresses on coastal water resources include water use restrictions, saline intrusions, and permanently modifying or damaging regional resources. Groundwater in coastal regions is often the only freshwater resource available, so an in-depth understanding of the aquifer, and the aquifer’s response to climate change, is essential for decision-makers. In this study, we focus on the coastal aquifer of Roussillon (southern France) by developing and investigating a steady-state groundwater flow model (MODFLOW 6) and calibrated with PEST++ on a Python interface (FloPy and PyEmu). Model input and boundary conditions are constrained by various scenarios of climate projections by 2080, with model results predicting the aquifer’s response (and associated uncertainty) to these external forcings. Using simple assumptions of intrusion estimates, model results highlight both strong climatic and anthropogenic impacts on the water table. These include aquifer drawdowns reaching several meters locally, and the seawater interface advancing locally several hundred meters inland and rising by several meters. Intrusions of this magnitude risk endangering exploited water wells and their sustainability. Our results demonstrate the critical importance of properly characterizing the geology and its heterogeneity for understanding aquifers at risk because poor predictions may lead to inappropriate decisions, putting critical resources at risk, particularly in coastal environments.</jats:p
Meaning differences between English clippings and their source words: A corpus-based study
No full textThis paper uses corpus data and methods of distributional semantics in order to study English clippings such as dorm (< dormitory),
memo (< memorandum), or quake (< earthquake). We investigate whether systematic meaning differences between clippings and
their source words can be detected. The analysis is based on a sample of 50 English clippings. Each of the clippings is represented
by a concordance of 100 examples in context that were gathered from the Corpus of Contemporary American English. We compare
clippings and their source words both at the aggregate level and in terms of comparisons between individual clippings and their source
words. The data show that clippings tend to be used in contexts that represent involved text production, which aligns with the idea that
clipped words signal familiarity with their referents. It is further observed that individual clippings and their source words partly diverge
in their distributional profiles, reflecting both overlap and differences with regard to their meanings. We interpret these findings against
the theoretical background of Construction Grammar and specifically the Principle of No Synonymy