Importance of ecological niche and environmental cues linked to resource localisation in the successful invasion of Drosophila suzukii : details for mass trapping development

Ces dernières années ont vu le développement du commerce international entraînant une accélération des mouvements intercontinentaux d'espèces. Ces multiples introductions sont à l'origine de nombreux cas d'invasion, où les espèces s'établissent et se dispersent. Dans le nouvel environnement, étudier les facteurs liés à la niche écologique permet de comprendre comment se déroule l'établissement des espèces introduites au sein de la communauté d'espèces résidentes. L'hypothèse de la niche vide, qui prédit que l'invasion est possible car un espace vide existe au sein des niches écologiques de la communauté résidente, est un des facteurs facilitants de nombreux cas d'invasion. Par ailleurs, la stratégie d'exploitation de la ressource par l'espèce invasive au sein de la niche écologique peut aussi expliquer la propension d'une espèce à envahir ou non le nouvel environnement. L'objectif de cette thèse est d'explorer l'importance de ces hypothèses dans le succès invasif, au travers de l'exemple de Drosophila suzukii. Introduite en 2008 en Europe et aux Etats-Unis, cette espèce a envahi chacun des continents en moins de 7 ans. Elle est la seule espèce européenne de drosophiles capable de pondre à l'intérieur de fruits sains omniprésents, au sein d'une niche écologique vide de tout compétiteur. Elle est à l'origine de gros problèmes pour la culture de fruits cultivés et se retrouve être l'un des ravageurs majeurs en production de fruits rouges. Mieux comprendre son invasion, sa niche écologique et sa stratégie de sélection d'habitat permet de mieux lutter contre l'insecte, notamment par des méthodes permettant de perturber la localisation des fruits dans l'environnement. Cet aspect appliqué est aussi un objectif important de cette thèse CIFRE, financée pour optimiser la lutte par piégeage massifIn the last few decades, the development of international trade has seen resulting in an acceleration of intercontinental movements of species. These multiple introductions are the cause of many cases of invasion, where species are established and spread. In the new environment, studying factors related to the ecological niche help understanding what happens during the establishment of introduced species within the community resident species. The “empty niche hypothesis”, which predicted that the invasion is possible because a gap exists in the ecological niches of the resident community, is one of the facilitating factors of many cases of invasion. In addition, the strategy of utilization of the resource by the invasive species in the ecological niche may also explain the propensity of a species to invade or not the new environment. The objective of this thesis is to explore the significance of these assumptions in the invasive success, through the example of Drosophila suzukii. Introduced in 2008 in Europe and the US, this species has invaded every continent in less than 7 years. It is the only European species of fruit flies that can lay eggs inside healthy fruits, which are omnipresent, in an ecological niche free of any competitor. It is the cause of dreadful issues for grown fruit and is one of the major pests in production of berries. Better understand its invasion, its ecological niche and habitat selection strategy help better fighting the insect, including methods to disrupt the location of fruit in the environment. This applied context is also an important aspect of this thesis, funded also to optimize the fight by mass trappin

Implication de la niche écologique et des indices environnementaux liés à la localisation de la ressource dans le succès invasif du ravageur Drosophila suzukii : des pistes pour le développement du piégeage massif

In the last few decades, the development of international trade has seen resulting in an acceleration of intercontinental movements of species. These multiple introductions are the cause of many cases of invasion, where species are established and spread. In the new environment, studying factors related to the ecological niche help understanding what happens during the establishment of introduced species within the community resident species. The “empty niche hypothesis”, which predicted that the invasion is possible because a gap exists in the ecological niches of the resident community, is one of the facilitating factors of many cases of invasion. In addition, the strategy of utilization of the resource by the invasive species in the ecological niche may also explain the propensity of a species to invade or not the new environment. The objective of this thesis is to explore the significance of these assumptions in the invasive success, through the example of Drosophila suzukii. Introduced in 2008 in Europe and the US, this species has invaded every continent in less than 7 years. It is the only European species of fruit flies that can lay eggs inside healthy fruits, which are omnipresent, in an ecological niche free of any competitor. It is the cause of dreadful issues for grown fruit and is one of the major pests in production of berries. Better understand its invasion, its ecological niche and habitat selection strategy help better fighting the insect, including methods to disrupt the location of fruit in the environment. This applied context is also an important aspect of this thesis, funded also to optimize the fight by mass trappingCes dernières années ont vu le développement du commerce international entraînant une accélération des mouvements intercontinentaux d'espèces. Ces multiples introductions sont à l'origine de nombreux cas d'invasion, où les espèces s'établissent et se dispersent. Dans le nouvel environnement, étudier les facteurs liés à la niche écologique permet de comprendre comment se déroule l'établissement des espèces introduites au sein de la communauté d'espèces résidentes. L'hypothèse de la niche vide, qui prédit que l'invasion est possible car un espace vide existe au sein des niches écologiques de la communauté résidente, est un des facteurs facilitants de nombreux cas d'invasion. Par ailleurs, la stratégie d'exploitation de la ressource par l'espèce invasive au sein de la niche écologique peut aussi expliquer la propension d'une espèce à envahir ou non le nouvel environnement. L'objectif de cette thèse est d'explorer l'importance de ces hypothèses dans le succès invasif, au travers de l'exemple de Drosophila suzukii. Introduite en 2008 en Europe et aux Etats-Unis, cette espèce a envahi chacun des continents en moins de 7 ans. Elle est la seule espèce européenne de drosophiles capable de pondre à l'intérieur de fruits sains omniprésents, au sein d'une niche écologique vide de tout compétiteur. Elle est à l'origine de gros problèmes pour la culture de fruits cultivés et se retrouve être l'un des ravageurs majeurs en production de fruits rouges. Mieux comprendre son invasion, sa niche écologique et sa stratégie de sélection d'habitat permet de mieux lutter contre l'insecte, notamment par des méthodes permettant de perturber la localisation des fruits dans l'environnement. Cet aspect appliqué est aussi un objectif important de cette thèse CIFRE, financée pour optimiser la lutte par piégeage massi

Modeling of the chemical behavior of sodium fire aerosols during atmospheric dispersion

International audienceThe use of liquid sodium as a coolant in sodium-cooled fast reactors (SFR) circuits requires studying the consequences of a sodium fire for safety analysis, and particularly the toxicological impact of sodium fire aerosols. More particularly, the carbonation of sodium fire aerosols from sodium hydroxide (NaOH) to sodium carbonate (Na$_2$CO$_3$) is investigated. A new kinetic model, based on the CO$_2$ reactive absorption and the two-film theory, is developed to describe the carbonation process of NaOH solutions, taking into account the NaOH aerosols' initial characteristics in equilibrium with the atmosphere. This model is applied for the case of NaOH aerosols considering the CO$_2$ absorption at the particle external surface. The estimation for the model parameters is detailed as function of NaOH degree of conversion, relative humidity (RH), and temperature. By comparisons with available experimental data, the absorption interfacial area is empirically estimated over the studied range of RH and initial particle diameter. The global sensitivity study of the model confirms its capabilities to describe NaOH aerosols' carbonation, waiting for new experimental data for validation

Where and what to feed? Differential effects on fecundity and longevity in the invasive Drosophila suzukii

Successful establishment of invasive species requires that the species meet environmental conditions favouring their longevity and fecundity. When juveniles and adults consume different resources, gravid females may have to choose whether to feed or to reproduce. We used a successful invasive species to test whether female life history traits are affected by the potential nutrients found in reproductive sites. The pest species, Drosophila suzukii, lays eggs in fruits that could provide nutrients since fruit exudates are generated during oviposition. We demonstrated that D. suzukii adults cannot survive when they have only access to reproductive sites (i.e. undamaged fruits). But they can find the nutrients necessary for longevity on these reproductive sites if there are larger holes in the exocarp. Egg maturation is low when D. suzukii feeds on nutrients from fruits, even when damaged, suggesting that females cannot acquire sufficient nutrients for egg maturation where they lay their eggs. Finally, a field experiment supported our laboratory results: wild females have a low degree of egg maturation, even when captured near reproductive sites. Our study hence shows constraints on egg production, and therefore on fruit infestation, determined by the nutritional ecology of pest females. (C) 2016 Gesellschaft fur Okologie

Data from: Microsatellite evolutionary rate and pattern in Schistocerca gregaria inferred from direct observation of germline mutations

Unravelling variation among taxonomic orders regarding the rate of evolution in microsatellites is crucial for evolutionary biology and population genetics research. The mean mutation rate of microsatellites tends to be lower in arthropods than in vertebrates, but data are scarce and mostly concern accumulation of mutations in model species. Based on parent-offspring segregations and a hierarchical Bayesian model, the mean rate of mutation in the orthopteran insect Schistocerca gregaria was estimated at 2.1e-4 per generation per untranscribed dinucleotide locus. This is close to vertebrate estimates and one order of magnitude higher than estimates from species of other arthropod orders, such as Drosophila melanogaster and Daphnia pulex. We also found evidence of a directional bias towards expansions even for long alleles and exceptionally large ranges of allele sizes. Finally, at transcribed microsatellites, the mean rate of mutation was half the rate found at untranscribed loci and the mutational model deviated from that usually considered, with most mutations involving multistep changes that avoid disrupting the reading frame. Our direct estimates of mutation rate were discussed in the light of peculiar biological and genomic features of S. gregaria, including specificities in mismatch repair and the dependence of its activity to allele length. Shedding new light on the mutational dynamics of grasshopper microsatellites is of critical importance for a number of research fields. As an illustration, we showed how our findings improve microsatellite application in population genetics, by obtaining a more precise estimation of S. gregaria effective population size from a published data set based on the same microsatellites

How varying parameters impact insecticide resistance bioassay: An example on the worldwide invasive pest Drosophila suzukii.

Monitoring pesticide resistance is essential for effective and sustainable agricultural practices. Bioassays are the basis for pesticide-resistance testing, but devising a reliable and reproducible method can be challenging because these tests are carried out on living organisms. Here, we investigated five critical parameters and how they affected the evaluation of resistance to the organophosphate phosmet or the pyrethroid lambda-cyhalothrin using a tarsal-contact protocol on Drosophila suzukii, a worldwide invasive pest. Three of the parameters were related to insect biology: (i) sex, (ii) age of the imago (adult stage) and (iii) genetic diversity of the tested population. The two remaining parameters were linked to the experimental setup: (iv) the number of individuals tested per dose and (v) the duration of exposure to the active ingredient. Results showed that response to insecticide differed depending on sex, males being twice as susceptible to phosmet as females. Age principally affected young females' susceptibility to phosmet, because 0-24 hour-old flies were twice as susceptible as 24-48 hour-old and 72-96 hour-old females. Genetic diversity had no observable effect on resistance levels. The precision and accuracy of the median lethal dose (LD50) were greatly affected by the number of individuals tested per dose with a threshold effect. Finally, optimal duration of exposure to the active ingredient was 24 h, as we found an underestimation of mortality when assessed between 1 and 5 h after exposure to lambda-cyhalothrin. None of the main known point mutations on the para sodium channel gene associated with a knockdown effect were observed. Our study demonstrates the importance of calibrating the various parameters of a bioassay to develop a reliable method. It also provides a valuable and transferable protocol for monitoring D. suzukii resistance worldwide

Spatial and temporal spread of maize stem borer Busseola fusca (Fuller) (Lepidoptera: Noctuidae) damage in smallholder farms

International audienceThe main purpose of this study was to understand the spatio-temporal spread of the maize stem borer Busseola fusca (Fuller) (Lepidoptera: Noctuidae) in smallholder maize farms. The analysis carried out allowed the establishment of complementary sampling scheme and analysis that can be applied to investigate the propagation of stem borer damages and extended to other insect pests. This approach requires consideration of all plants point locations, the knowledge on the level of damage and its characterization. Results showed that there was a two-week interval between occurrence of the peaks of leaf damage and male adult moth abundance. The prior role of leaf damages in the farm infestation by B. fusca is revealed, and an estimate of the mean transition time between different damage types is provided. Furthermore, damaged plants exhibited a local spatial autocorrelation within a range of dependence of 0-10 meters; and the spatio-temporal pattern of B. fusca damage spread evolves as a spiral around an initial patch of damaged plants. By assuming a neighbor configuration of distribution of damaged plants nearby non-damaged, we showed that the inner plants are likely to become damaged within a time period of a week; thus, B. fusca infests farms in a systematic fashion. Overall, these results have useful implications for improving and optimizing existing field sampling methods for insect pest damages. The approaches used in carrying out the analysis further provided a deep understanding helpful to improve integrated pest management (IPM) strategies against stem borers, and offer IPM practitioners’ the opportunity to design, develop, and implement optimum control methods against B. fusca, an important pest of maize in Africa

All or nothing: Survival, reproduction and oxidative balance in Spotted Wing Drosophila (Drosophila suzukii) in response to cold

International audienceWinter severity and overwintering capacity are key ecological factors in successful invasions, especially in ectotherms. The integration of physiological approaches into the study of invasion processes is emerg- ing and promising. Physiological information describes the mechanisms underlying observed survival and reproductive capacities, and it can be used to predict an organism’s response to environmental per- turbations such as cold temperatures. We investigated the effects of various cold treatments on life his- tory and physiological traits of an invasive pest species, Drosophila suzukii, such as survival, fertility and oxidative balance. This species, a native of temperate Asian areas, is known to survive where cold tem- peratures are particularly harsh and has been recently introduced into Europe and North America. We found that cold treatments had a strong impact on adult survival but no effect on female’s fertility. Although only minor changes were observed after cold treatment on studied physiological traits, a strong sex-based difference was observed in both survival and physiological markers (antioxidant defences and oxidative markers). Females exhibited higher survival, reduced oxidative defences, less damage to nucleic acids, and more damage to lipids. These results suggest that D. suzukii relies on a pathway other than oxidative balance to resist cold injury. Altogether, our results provide information concerning the mech- anisms of successful invasion by D. suzukii. These findings may assist in the development of population models that predict the current and future geographic ranges of this species