<i>Horismenus</i> species (Hymenoptera: Eulophidae) in a bruchid beetle parasitoid guild, including the description of a new species

Four species of Horismenus (Hymenoptera: Eulophidae) associated with Acanthoscelides spp.(Coleoptera: Bruchidae), three of which are also associated with Phaseolus spp., are treated. One of the species, H. butcheri, is described as new and the remaining three species are redescribed. Allfour species are diagnosed in a key. A lectotype is designated for Holcopelte productus Ashmead

Arthropod symbioses: a neglected parameter in pest- and disease-control programmes

1. Arthropods are important players in biological control as pests, control agents and transmitters of invertebrate diseases. Arthropods are frequently infected with one or several micro-organisms, serving as micro-ecosystems in which multiple interactions can take place. These micro-organisms include disease agents and symbiotic micro-organisms. The latter are usually vertically transmitted and can have a broad spectrum of effects on their hosts, ranging from reproductive manipulations to protection against natural enemies. These interactions may directly or indirectly alter the biology of many arthropods in agriculturally, medically and ecologically relevant ecosystems. 2. Symbiotic micro-organism-induced reproductive manipulations such as cytoplasmic incompatibility and parthenogenesis induction can substantially affect the rearing of biological control agents. Many insects, and recently also mites and nematodes, have been found to be infected, displaying a wide range of effects. We discuss examples of arthropod-micro-organism interactions and effects, which could have consequences for the practical application of arthropods in biological control. 3. Symbiotic micro-organisms can also be involved in host protection against natural enemies such as parasitoids, pathogenic bacteria, fungi and viruses. 4. Symbiotic bacteria can influence the vectorial capacity of disease-vectoring arthropods and may be very helpful in decreasing the transmission of disease agents. 5. Synthesis and applications. The effect of micro-organisms on the outcome of biological control programmes is usually not considered in risk assessments and failure analyses. This review emphasizes the importance of endosymbiotic micro-organisms in comprehensive biological control programmes and provides recommendations on how to recognize, avoid or benefit from these influential tenants

Isolation and characterization of polymorphic microsatellite loci in <i>Acanthoscelides obvelatus</i> Bridwell (Coleoptera: Bruchidae)

Five microsatellite loci were isolated from the bruchid Acanthoscelides obvelatus Bridwell (Coleoptera: Bruchidae). Each locus was polymorphic, with the number of alleles ranging from two to 15. We found high levels of within-population variation at most loci, with heterozygosity ranging from 0.182 to 0.900. Cross-species amplification of these loci was tested in two other species of the genus Acanthoscelides, A. obtectus Say and A. argillaceus Sharp

Native and introduced parasitoids attacking the invasive chestnut gall wasp <i>Dryocosmus kuriphilus</i>

The globally invasive chestnut gall wasp Dryocosmus kuriphilus was recently reported in Italy and threatens European chestnut orchards and native forests. Of Chinese origin, this species has invaded Japan, Korea, the USA, Nepal and Europe and in each region it has been attacked by parasitoids exploiting oak gall wasps. Classical biological control using the parasitoid Torymus sinensis (Hymenoptera: Torymidae) successfully reduced infestation in Japan. Subsequent work in Japan and Korea showed this parasitoid to represent a poorly understood and biologically diverse species complex. Following its success in Japan, T. sinensis was released in Italy in 2005. A growing appreciation of the taxonomic and ecological complexity of the T. sinensis complex in Japan and Korea has stimulated ongoing DNA-based work on relationships and interbreeding of species in this group. Oak cynipid parasitoids provide potential for native augmentative or conservation biological control of D. kuriphilus in Europe. Exploitation of this potential requires improved understanding of the taxonomy of these parasitoids, particularly of morphologically highly conserved lineages such as Eurytoma and Eupelmus in which recognised species may contain many cryptic lineages. There is a growing need for a molecular survey of the communities centered on chestnut and oak gall wasps to: (1) ascertain the identity of T. sinensis lineages released in Italy (2) track the dispersal of T. sinensis in the native community, either in its original form or as hybrids with native species (3) identify possible biological control agents in the native parasitoid community

The potential of native parasitoids for the control of Mexican bean beetles: A genetic and ecological approach

Bruchid beetles in the genus Zabrotes are important pests of field and stored beans all around the world and cause enormous economical losses in Mexico and Central America. Native parasitoids have been successfully used to suppress infestations by bruchid beetles in Africa, but few studies have assessed their potential to reduce seed damage in the New World and no successful biological control programs have been implemented, mainly due to the poor knowledge on their biology, systematics and ecology in this region. In this study, we used molecular tools to describe a new complex of three parasitoid species of bruchid beetles in the genus Horismenus, and investigated the level of gene flow and presence of ecotypes in this complex. We also examined the specific association between species of Horismenus and two sibling species of Zabrotes beetles, in order to evaluate their potential as biological control agents. Microsatellite data support the previous morphological description of three species, H. butcheri, H. missouriensis and H. depressus, but suggest some gene flow between H. missouriensis and H. depressus. Host-plant is shown to be the most important factor determining the ecological distribution of the two Zabrotes species, whereas altitude explains most of the distribution of the three Horismenus species. These results complement our understanding of this tritrophic system, providing a solid base for a potential biological control program using native parasitoids

Evolution of the "Castanea sativa" - "Dryocosmus kuriphilus" - "Torymus sinensis" - system in southern Switzerland

L’arrivée de nouveaux organismes qui peuvent s’avérer potentiellement nuisibles à l’égard des personnes et des écosystèmes est devenu un objet de préoccupation quotidienne, à tel point qu’il existe en Suisse environ 800 espèces reconnues d’organismes étrangers, dont au moins 107 sont considérées invasives. Pour maîtriser ce genre d’insectes nuisibles l’une des méthodes possibles consiste à importer et introduire des ennemis naturels provenant de leur pays d’origine en leur permettant d’agir en tant qu’agents de lutte biologique. Un excellent exemple type est le cas récent du cynips du châtaignier originaire d’Asie (Dryocosmus kuriphilus Yasumatstu) qui a fait son arrivée en 2002 en Europe et qui a été combattu avec l’importation de son ennemi naturel Torymus sinensis Kamijo Malgré la présence d’un grand nombre d’études menées par les chercheurs japonais, au moment où j’ai commencé cette thèse, nous ne disposions que de connaissances limitées sur l’ensemble des dégâts provoqués par des attaques répétées du cynips et sur la capacité de reprise de l’arbre-hôte (Castanea sativa Miller) lorsque la lutte biologique atteint son but. L’objectif de cette thèse est donc d’étudier et de présenter l’évolution des forêts de châtaignier, de l’arrivée du ravageur jusqu’au contrôle biologique, en mettant en évidence l’ensemble des dégâts subis par l’arbre, ses modalités de reprise et les effets considérables qu’une lutte biologique tardive peut entraîner. Nous nous sommes d’abord concentrés (chap.2) sur la partie méthodologique en recherchant les meilleurs indicateurs pour analyser l’évolution épidémique sur le châtaignier, en particulier sur le plan des dégâts et des processus de réparation. Plus précisément, nous avons utilisé la relation aire foliaire-section d’aubier en nous basant sur l’approche du pipe model pour faire une estimation quantitative de la biomasse verte d’une branche avant et après l’arrivée de l’insecte nuisible, y compris pendant la période de pic de l’épidémie et la première et deuxième année de rétablissement grâce l’action progressive de T. sinensis. Ensuite, la perte de la surface foliaire a été utilisée comme variable réponse dans une analyse de modèle de régression mixte pour choisir les caractéristiques architecturales les plus appropriées (par ex. le type de galle, le type de bourgeon, le type de pousse) permettant d’expliquer l’évolution des dégâts au niveau des branches. Les résultats ont montré que durant le pic de l’épidémie, les pertes de la surface foliaire excédaient 70% avec des altérations significatives de l’architecture des branches en fait de bourgeons dormants (réserves de l’arbre) et d’augmentation de pousses mortes. De plus notre analyse a révélé que les indicateurs traditionnellement utilisés et généralement mentionnés dans la littérature pour mesurer le taux d’infestation du cynips du châtaignier (par ex. le nombre de bourgeons infestés vs le nombre de bourgeons sains) ne parviennent pas à fournir une estimation fiable de la perte effective de surface foliaire, tandis que la combinaison de trois caractéristiques architecturales des branches d’un arbre (galles, pousses mortes, bourgeons dormants) dans un index composé (DCI) permet d’obtenir une évaluation beaucoup plus réaliste des dégâts subis par les branches pendant toute la durée de l’épidémie. Ce chapitre se conclut par une réflexion sur le sens et l’utilité des index disponibles (DCI, taux d’infestation, transparence de la couronne). Simultanément (chap.3) nous nous sommes penchés sur la procédure habituelle de vérification de la présence du parasite par dissection de galles recueillies sur le terrain; ainsi nous avons optimisé le nombre de galles à récolter pour évaluer avec précision le taux de parasitisme de T. sinensis aux dépens de D. Kuriphilus. À l’aide d’une approche de substitution spatio-temporelle (space-for-time substitution approach) nous avons utilisé 15 sites pour créer un suivi temporel (temporal) qui nous a permis de reconstruire les phases principales du développement de la population de T. sinensis, à partir du moment de son arrivée ou du lâcher sur le site jusqu’à son établissement et son contrôle complet sur la population du cynips. À l’aide de simulations de bootstrap, nous avons analysé la précision que différents essais d’échantillonnage (par ex. quantité de galles à récolter) pouvaient conférer à l’évaluation du succès des lâchers de T. sinensis (détection de l’insecte dans les galles) et sur l’évolution de son taux de parasitisme pendant l’établissement et la croissance de sa population jusqu’à ce que la lutte biologique soit achevée. Les résultats ont démontré qu’après le premier lâcher, 200 galles suffisent pour évaluer en toute confiance sa présence, tandis que lorsque les populations de T. sinensis deviennent stables, 100 galles suffisent pour évaluer son taux de parasitisme. L’évolution du système Castanea sativa – Dryocosmus kuriphilus – Torymus sinensis, de l’arrivée de l’insecte nuisible à la situation après quatre ans de lutte biologique (chap.4), a ensuite été analysée en utilisant les index décrits dans les chapitres précédents sur 15 sites choisis sur une grille de 10 x 10 km de manière à couvrir toute la surface du nord au sud de la Suisse méridionale. Les résultats montrent que la dynamique de la population de T. sinensis (chap. 4.1) affiche une croissance exponentielle avec différents taux en fonction de la distance du site italien de lâcher le plus proche et, partiellement, de l’abondance du cynips. De ce fait le temps requis pour atteindre le seuil de lutte biologique depuis l’arrivée de T. sinensis s’est révélé beaucoup plus court (seulement deux ans) pour les peuplements des régions du nord que pour ceux du sud (sept ans) qui ont donc subi de plus graves dommages. Une fois que la population de T. sinensis devient consistante, le contrôle exercé sur le cynips semble garantir un niveau d’infestation bas et stable avec de légères fluctuations. À la longue les deux populations baissent sensiblement en termes de nombres absolus à tel point qu’il devient presqu’impossible de trouver des galles. En ce qui concerne le châtaignier (chap. 4.2) les dégâts varient en fonction du temps écoulé entre l’arrivée du cynips et le contrôle biologique par T. sinensis. Plus précisément, les arbres qui se trouvent sur des sites où les attaques incontrôlées du cynips se sont répétées pendant sept ans présentent des portions importantes de couronne mourante et des réactions provoquées par le stress (par ex., rejets le long du tronc) alors que sur les sites où les deux insectes sont arrivés presque simultanément, les dégâts sont inférieurs et presque imperceptibles. Enfin, les effets importants du contrôle tardif du cynips sur six sites suisses se sont vérifiés par la perte temporaire de produits typiques tel que le miel de châtaignier monofloral (chap.5). Nous avons en particulier déterminé la composante due au châtaignier dans la composition du miel à l’aide d’une approche combinée chimique et sensorielle, et nous avons mis en relation les résultats obtenus avec les index de dégâts. Les statistiques ont montré que la présence de la châtaigne dans la composition du miel diminue de manière significative à partir d’un niveau d’infestation de D. kuriphilus de 30%, tandis que la production du typique miel de châtaignier monofloral devient presqu’impossible dans le secteur observé par l’analyse lorsque les dégâts atteignent 40% et plus. En synthèse cette thèse fournit de nouvelles connaissances sur les dégâts causés par le cynips au châtaignier en présentant les retombées écologiques (et culturelles) lorsque la lutte contre l’insecte advient avec un certain retard. Elle contribue également à éclaircir la méthodologie adoptée pour évaluer correctement l’impact global de l’épidémie causée par le cynips. Enfin et surtout, elle présente un cas de lutte biologique réussie dans un système agroforestier. Pour finir, quelques lignes de recherche future sont formulées dans le chapitre conclusif.The arrival of new organisms that may potentially become harmful for people and ecosystems has become a world-wide daily concern to the point that in Switzerland about 800 established alien species exist, of which at least 107 are considered invasive. A possible way to control such pests is by importing and releasing natural enemies from their countries of origin, letting them to act as so-called biocontrol agents. The discovery in 2002 of the Asian chestnut gall wasp (Dryocosmus kuriphilus Yasumatsu) in Europe and the subsequent importation of its natural enemy Torymus sinensis Kamijo is a prime example in this sense. Even though a lot of studies have already been done by Japanese researchers, when I started my thesis, there was poor knowledge on the overall damages due to repeated D. kuriphilus attacks as well as on the reactions and recovery patterns of the host tree (Castanea sativa Miller) when the biocontrol is reached. Therefore the aim of this thesis is to present the evolution of the chestnut forests from the arrival of the pest to the biological control, highlighting the overall tree damages, its recovery patterns and the far-reaching effects that a delayed pest control can cause. We first focused (chapter 2) on the methodological part by studying the best indices to analyze the epidemic evolution on the chestnut tree, especially in terms of damages and recovery pattern. Specifically, we used the leaf to sapwood area relationship based on the pipe model approach to quantitatively estimate the green biomass of a branch before the arrival and after the arrival of the pest, including the epidemic peak and the first and second year of recovery due to the progressive biological control by T. sinensis. Leaf area loss has then been used as a response variable in a mixed regression model analysis, to select the most suitable explanatory architectural features (e.g. gall types, bud types, shoot types) explaining the damage evolution at branch level. Results showed that during the epidemic peak, leaf area losses exceeded 70%, with significant alterations in branch architecture in terms of reduction of dormant buds (tree reserves) and increase of dead shoots. Moreover, the model analysis revealed that the traditional damage assessment based on the infestation rate (e.g. number of infested buds vs number of buds) usually reported in literature fails to provide a sound estimation of effective leaf area loss, whereas the combination of three branch architectural features (galls, dead shoots, dormant buds) in a damage composite index (DCI) enables a by far more realistic assessment of the branch damages during the entire epidemic process. We concluded discussing the meaning and the usefulness of the available indexes (DCI, infestation rates, Crown transparency). Simultaneously (chapter 3), the gall collection approach has been tailored to optimize the time-consuming procedure to evaluate D. kuriphilus parasitism by T. sinensis, which typically consists of dissecting galls collected in the field and checking its presence on them. Using a space-for-time substitution approach we used 15 sites to create a temporal which allowed us to reconstruct the main phases of the T. sinensis population development, from its release or arrival in a site to its complete establishment and control of the pest population. By the means of bootstrap simulations, we analyzed the effect of different sampling efforts on the precision of evaluating the success of T. sinensis release and the evolution of its parasitism rate towards biocontrol. Results show that after the first release, 200 galls are required to confidently assess its presence whereas once T. sinensis is well established 100 galls are sufficient to estimate its parasitism rate. The evolution of the Castanea sativa – Dryocosmus kuriphilus – Torymus sinensis system from the pest arrival to the situation of four-year biocontrol (chapter 4) has then been analyzed by using the indices described in the previous chapters in 15 sites selected on a grid of 10 x 10 km so as to cover the entire southern Switzerland area from north to south. Results show that the population dynamics of T. sinensis (chapter 4.1) displays an initial exponential growth at different rates as a function of the distance from the nearest Italian release site and partially of the D. kuriphilus abundance. Consequently, the time needed to reach the biocontrol threshold since the T. sinensis arrival was much shorter (only two years) for the northern populations than for the southern one (seven years), which consequently experienced more severe damages. Once the T. sinensis population becomes massive and stable, the control exerted on D. kuriphilus seems to guarantee a low and stable infestation level with small fluctuations. On the long run both populations become very low in terms of absolute numbers to the point that galls become almost impossible to find. From the chestnut point of view (chapter 4.2) damages vary as a function of the time elapsed between pest arrival and biological control by T. sinensis. Specifically, trees in sites experiencing seven years of D. kuriphilus uncontrolled attacks show larger dying crown portions and stress-induced reactions (e.g., suckers along the stem) compared to sites where the two insects arrived nearly simultaneously. Finally, the far-reaching effects of the delayed pest control in six Swiss sites are highlighted in the temporary loss of typical products such as the unifloral chestnut honey (chapter 5). Specifically, we determined the chestnut component in honey via a combined chemical and sensory approach and related the obtained results with the damage indices. Decreases in the chestnut component of the honey were statistically significant starting from a D. kuriphilus infestation level of 30%, whereas the production of the typical unifloral chestnut honey became almost impossible in the study area when damages raised to 40% or higher. Overall, this thesis provides some new knowledge on the damages caused by D. kuriphilus on the chestnut tree, highlighting possible ecological (and cultural) far-reaching effects caused by a delayed pest control. It also sheds some light on the methodology to properly evaluate the overall impact of the pest epidemic. Last but not least, it shows a successful biocontrol story in an agroforestry system. Finally, some future research lines are given in a concluding chapter

Des abeilles, des ruches et des humains: les Centres apicoles : des acteurs de la réalisation de la filière apicole au Burkina Faso

La présente étude se focalise sur les processus de structuration de la filière apicole au Burkina Faso et sur le rôle joué par les Centres apicoles ; des structures nées en tant qu’unités de transformation des premiers projets de développement en apiculture élaborés par certaines ONG étrangères durant la fin des années 1990 et le début des années 2000. En partant du constat que tout projet dans sa réalisation possède un degré d’imprévisibilité, je tente d’explorer la manière dont les Centres apicoles agissent aujourd’hui au sein de différentes arènes de négociation pour stabiliser leur rôle, celui des autres acteurs, comme par exemple les apiculteurs et les abeilles et leur projet de filière de commercialisation du miel. Après les observations de terrain et la récolte de récits des principaux protagonistes de la filière, j’essaye de restituer, à travers trois axes d’analyse, le dynamise et la complexité du développement de l’espace apicole burkinabé dans lequel les Centres apicoles s’insèrent en tant qu’acteurs incontournables, tout en présentant en même temps un certain degré de fragilité. Le premier axe se focalise sur le travail de stabilisation d’un réseau d’apiculteurs producteurs exercé par les représentants des Centres apicoles. Le deuxième se concentre sur les processus d’intermédiation que les dirigeants de ces structures entretiennent avec les membres d’organismes de développement en vue de pouvoir contrôler et diriger la redistribution des appuis au sein de la filière apicole. Le troisième s’intéresse à la normalisation de la filière apicole à l’échelle nationale. Dans cette dernière partie je m’interroge également sur rôle de l’abeille et de son environnement dans la réalisation ou la déréalisation de la filière apicole et des interventions d’ONG actives dans le domaine du développement de l’apiculture.This study focuses on the processes of structuring the beekeeping sector in Burkina Faso and the role played by beekeeping centres; structures created as processing units within the first development projects in beekeeping designed by some foreign NGOs in the late 1990s and early 2000s.Starting from the assumption that every project, in its implementation, has a degree of unpredictability, I try to explore the way in which beekeeping centres today act within different negotiating arenas to stabilize their honey marketing chain project, their role and that of other actors, such as beekeepers. After field observations and the collection of data from the main protagonists of the sector, I try to restore, through three axes of analysis, the dynamism and complexity of the development of the beekeeping industry of Burkina Faso. Sector in which the beekeeping centres are inserted as essential actors, while at the same time presenting a certain degree of fragility. The first axis focuses on the work of representatives of beekeeping centres to stabilise a network of beekeepers. The second focuses on the intermediation processes that the leaders of these structures maintain with members of development organizations in order to manage and direct the redistribution of aid within the beekeeping sector. The third is concerned with the standardization of the beekeeping sector at the national level. In this last part I also examine the role of the bee and its environment in the realization or derealization of the beekeeping sector

The role of the bacterial community in the nutritional ecology of the bulb mite <i>Rhizoglyphus robini</i> (Acari: Astigmata: Acaridae)

The biology of many arthropods can only be understood when their associated microbiome is considered. The nutritional requirements of the bulb mite Rhizoglyphus robini Claparede (Acari: Astigmata: Acaridae) in the laboratory have been shown to be very easily satisfied, and in the field the mites prefer fungus-infected over uninfected plants. To test whether symbiotic bacteria facilitate the survival of R. robini on a temporarily nutritionally unbalanced diet, we investigated the composition of its microbiome. Using 454 pyrosequencing of 16S rRNA gene fragments, 3 genera were found to dominate the bacterial community: Myroides (41.4%), Serratia (11.4%), and Alcaligenes (4.5%); the latter 2 are known to include chitinase-producing species. Laboratory experiments demonstrated that mite fecundity is significantly higher (2 times) on fungus than on controls (sterilized potato dextrose agar and filter paper). Also, when mite homogenate was applied to a chitin layer, the halo produced through degradation was clearly visible, while the saline control did not produce a halo. We thus concluded that R. robini utilizes fungal chitin, at least to a certain extent, as a food source with the help of its associated bacteria. This information supports the general concept of multigenome organisms and the involvement of bacteria in the mite's nutritional ecology

A worldwide survey of neonicotinoids in honey

Growing evidence for global pollinator decline is causing concern for biodiversity conservation and ecosystem services maintenance. Neonicotinoid pesticides have been identified or suspected as a key factor responsible for this decline. We assessed the global exposure of pollinators to neonicotinoids by analyzing 198 honey samples from across the world. We found at least one of five tested compounds (acetamiprid, clothianidin, imidacloprid, thiacloprid, and thiamethoxam) in 75% of all samples, 45% of samples contained two or more of these compounds, and 10% contained four or five. Our results confirm the exposure of bees to neonicotinoids in their food throughout the world. The coexistence of neonicotinoids and other pesticides may increase harm to pollinators. However, the concentrations detected are below the maximum residue level authorized for human consumption (average ± standard error for positive samples: 1.8 ± 0.56 nanograms per gram)

Evolution and diversity of <i>Rickettsia</i> bacteria

Background: Rickettsia are intracellular symbionts of eukaryotes that are best known for infecting and causing serious diseases in humans and other mammals. All known vertebrate-associated Rickettsia are vectored by arthropods as part of their life-cycle, and many other Rickettsia are found exclusively in arthropods with no known secondary host. However, little is known about the biology of these latter strains. Here, we have identified 20 new strains of Rickettsia from arthropods, and constructed a multi-gene phylogeny of the entire genus which includes these new strains. Results: We show that Rickettsia are primarily arthropod-associated bacteria, and identify several novel groups within the genus. Rickettsia do not co-speciate with their hosts but host shifts most often occur between related arthropods. Rickettsia have evolved adaptations including transmission through vertebrates and killing males in some arthropod hosts. We uncovered one case of horizontal gene transfer among Rickettsia, where a strain is a chimera from two distantly related groups, but multi-gene analysis indicates that different parts of the genome tend to share the same phylogeny. Conclusion: Approximately 150 million years ago, Rickettsia split into two main clades, one of which primarily infects arthropods, and the other infects a diverse range of protists, other eukaryotes and arthropods. There was then a rapid radiation about 50 million years ago, which coincided with the evolution of life history adaptations in a few branches of the phylogeny. Even though Rickettsia are thought to be primarily transmitted vertically, host associations are short lived with frequent switching to new host lineages. Recombination throughout the genus is generally uncommon, although there is evidence of horizontal gene transfer. A better understanding of the evolution of Rickettsia will help in the future to elucidate the mechanisms of pathogenicity, transmission and virulence