Etude d'un hôte de substitution dans le cadre d'un programme de lutte biologique contre Paysandisia archon, ravageur du palmier

Depuis quelques années nous assistons à la l’installation sur tout le pourtour méditerranéen d’une espèce de lépidoptère exotique originaire d’Amérique du sud : Paysandisia archon (Burmeister, 1880) (lépidoptère : Castniidae). Introduit en Europe dans les années 1990 par l’importation de palmiers d’ornementation, il cause aujourd’hui de sérieuses pertes sur les palmiers. Malgré des premiers résultats encourageant grâce à la lutte chimique, les moyens de lutte contre Paysandisia archon sont peu efficaces. Le stade le plus accessible permettant une action sur le ravageur, est le stade œuf, accessible pour les parasitoïdes durant plusieurs jours. L’élevage de parasitoïdes se faisant sur des œufs d’un hôte de substitution, il nécessaire de maitriser la biologie du cet hôte et synchroniser la production d’œufs avec les émergences programmées de parasitoïdes. Ainsi notre étude vise à déterminer le meilleur procédé pour la maitrise du développement de l’espèce Philosamia ricini et de la production d’œufs qui serviront à l’élevage de parasitoïdes contre le ravageur palmivore Paysandisia archon. Lors de notre étude nous avons étudié l’effet de différentes températures sur le cycle de développement de l’espèce P. ricini au cours des divers stades. En se basant sur nos résultats, il semble que la mise en place d’un ralentissement du cycle de développement soit possible. Cependant tous les stades ne sont pas manipulables de la même façon : Les cocons pourront être conservés à 10.5°C, 13°C ou 18°C, l’éclosion des œufs retardée à 18°C. Le cycle de développement des stades larvaires pourra être ralenti à 18°C avec un taux élevé d’humidité pour les jeunes stades (L1-L2) et avec un faible taux d’humidité pour les derniers stades (L4-L5). Ce ralentissement pourra se faire sur la durée d’un stade, voir sur quelques jours du stade afin d’éviter une trop forte mortalité. Bien que les résultats obtenus nous renseignent sur les meilleures possibilités de contrôle de la durée du cycle, des améliorations supplémentaires pourraient être apportées pour augmenter la production, le rendement et faciliter l’élevage

Shaping the antipredator strategy: flexibility, consistency, and behavioral correlations under varying predation threat.

9 pagesInternational audienceRecent ecological and evolutionary research emphasizes the importance of adaptive trait integration. For instance, antipredator defenses are built up of several morphological and behavioral components in many species, yet their functional relationships are still poorly documented. Using field-collected freshwater crustaceans Gammarus fossarum in a within-subject design, we investigated the flexibility and consistency of refuge use, photophobia, and exploration behavior as well as their associations, quantified both when predation risk was absent or artificially simulated. In agreement with the "threat-sensitivity" hypothesis, both refuge use and photophobia increased under predation risk, whereas exploration behavior did not vary. For all behaviors, individuals exhibited low but significant consistency between risk treatments. However, intraindividual variability did not vary with weight or between sexes. Finally, a positive relationship between photophobia and refuge use was observed only under predation risk in females, whereas it was found in both risk treatments in males. Our findings demonstrate that predation risk may promote behavioral flexibility and behavioral correlations, or syndromes, in wild populations, and call for an integrative study of antipredator mechanisms where the evolution of each dimension has to be examined in combination with all others. Additional phenotypic traits should be included in future studies to better characterize the multidimensionality of antipredator defense and the functional relationships among traits. The survival consequence of behavioral correlations between risk-sensitive traits also remains to be estimated in mortality selection experiments

Speed-accuracy trade-off and its consequences in a scramble competition context.

8 pagesInternational audienceAnimals foraging in groups commonly respond to the presence of others by increasing their foraging rate, an increase that could come at the expense of prey detection accuracy. Yet the existence and consequences of such so-called 'speed-accuracy trade-offs' in group-foraging animals remain unexplored. We used group-feeding zebra finches, Taeniopygia guttata, to determine how search speed affects food detection accuracy and how a potential speed-accuracy trade-off influences feeding success. We found significant between-individual differences in hopping speed as well as evidence that faster individuals were more likely to overlook food, demonstrating the existence of a trade-off between speed and food detection probability. We also found that feeding success was positively predicted by an individual's food detection probability, whereas it was unrelated to hopping speed. These findings have several implications. First, they indicate that social animals, like solitary foragers, may be affected by perhaps universal constraints when foraging, such as limited attention. These constraints may contribute to promote between-individual variation in foraging tactics within social groups. Second, the existence of a speed-accuracy trade-off suggests that between-individual behavioural differences are more likely to come from differential allocation between speed and accuracy than from differences in general intrinsic abilities to exploit food resources. Finally, scramble competition's outcomes are likely to be determined by a combination of foraging abilities that individuals must trade off against one another, calling for an integrative approach of how natural selection shapes interactive behavioural dimensions during foraging

Un parasitoïde oophage pour contrôler <em>Paysandisia archon</em> (Burmeister) : le trichogramme

National audienceDepuis son apparition en 2001, en région méditerranéenne, le papillon palmivore Paysandisia archon (Burmeister) poursuit sa progression en entrainant plus de dégâts et des pertes économiques importantes. Il est donc urgent de trouver une solution biologique pour contrôler ce ravageur, en respectant l’environnement et la santé humaine. Le stade œuf étant le plus accessible et précédant le stade larvaire phytophage, c’est un parasitoïde oophage qui est recherché. Les trichogrammes, dont l’efficacité a déjà été prouvée en lutte biologique sur différentes cultures, ont été testés. Les trichogrammes habituellement élevés sur l’hôte de substitution Ephestia kuehniella (Zeller) sont trop petits pour s’attaquer aux œufs de P. archon. Nous les avons alors élevés sur un nouvel hôte de substitution plus gros : Philosamia ricini (Drury). Nous avons confirmé l’augmentation de la taille des trichogrammes ainsi élevés (tibia et ovipositeur) et l’amélioration de leur fécondité, dès la première génération. C'est avec succès que ces Hyménoptères ont parasité des œufs de P. archon</em

Un parasitoïde oophage pour contrôler Paysandisia archon (Burmeister) : le trichogramme

National audienceSince its introduction in 2001, in Mediterranean region, the palmivore moth Paysandisia archon (Burmeister) continues to progress, resulting in more damages and economic losses. Therefore it is urgent to find a biological method to control this pest, respecting the environment and human health. The egg stage is the most accessible and the previous instar before phytophagous stage so an oophagous parasitoid is searched. Trichogramma, which effectiveness has been proven in biological control on different crops, have been tested. Trichogramma usually reared on the alternative host Ephestia kuehniella (Zeller), are too small to lay on the eggs of P. archon. We have therefore reared them on a new, larger substitution host Philosamia ricini (Drury). We confirmed the increase in the size of Trichogramma (tibia and ovipositor) and the improvment of their fecundity, as soon as the first generation. These wasps have successfully parasitized P. archon eggs.Depuis son apparition en 2001, en région méditerranénne, le papillon palmivore Paysandisia archon (Burmeister) poursuit sa progression en entrainant plus de dégâts et des pertes économiques importantes. Il est donc urgent de trouver une solution biologique pour contrôler ce ravageur, en respectant l’environnement et la santé humaine. Le stade oeuf étant le plus accessible et précédant le stade larvaire phytophage, c’est un parasitoide oophage qui est recherché. Les trichogrammes, dont l’efficacité a déjà été prouvée en lutte biologique sur différentes cultures, ont été testés. Les trichogrammes habituellement élevés sur l’hôte de substitution Ephestia kuehniella (Zeller) sont trop petits pour s’attaquer aux oeufs de P. archon. Nous les avons alors élevés sur un nouvel hôte de substitution plus gros : Philosamia ricini (Drury). Nous avons confirmé l’augmentation de la taille des trichogrammes ainsi élevés (tibia et ovipositeur) et l’amélioration de leur fécondité, dès la première génération. C'est avec succès que ces Hyménoptères ont parasité des oeufs de P. archon

La qualité et la diversité de la nutrition pollinique ont-elles un effet sur la santé de l'abeille ?

National audienc

Influence of pollen nutrition on honey bee health: do pollen quality and diversity matter?

Honey bee colonies are highly dependent upon the availability of floral resources from which they get the nutrients (notably pollen) necessary to their development and survival. However, foraging areas are currently affected by the intensification of agriculture and landscape alteration. Bees are therefore confronted to disparities in time and space of floral resource abundance, type and diversity, which might provide inadequate nutrition and endanger colonies. The beneficial influence of pollen availability on bee health is well-established but whether quality and diversity of pollen diets can modify bee health remains largely unknown. We therefore tested the influence of pollen diet quality (different monofloral pollens) and diversity (polyfloral pollen diet) on the physiology of young nurse bees, which have a distinct nutritional physiology (e.g. hypopharyngeal gland development and vitellogenin level), and on the tolerance to the microsporidian parasite Nosemaceranae by measuring bee survival and the activity of different enzymes potentially involved in bee health and defense response (glutathione-S-transferase (detoxification), phenoloxidase (immunity) and alkaline phosphatase (metabolism)). We found that both nurse bee physiology and the tolerance to the parasite were affected by pollen quality. Pollen diet diversity had no effect on the nurse bee physiology and the survival of healthy bees. However, when parasitized, bees fed with the polyfloral blend lived longer than bees fed with monofloral pollens, excepted for the protein-richest monofloral pollen. Furthermore, the survival was positively correlated to alkaline phosphatase activity in healthy bees and to phenoloxydase activities in infected bees. Our results support the idea that both the quality and diversity (in a specific context) of pollen can shape bee physiology and might help to better understand the influence of agriculture and land-use intensification on bee nutrition and health

Effect of pollen diet and <i>Nosema ceranae</i> infection on phenoloxidase.

<p>Box plots are shown for 3 pools of 3 bees/replicate (<i>n</i> = 9 replicates giving 81 bees total/pollen diet). Different letters denote significant differences between pollen diets in non-parasitized (white box plots) or <i>Nosema</i>-parasitized bees (grey box plots) (<i>p</i> < 0.05, Kruskal-Wallis and Dunn’s multiple comparison tests) and * indicate significant differences between parasitized and non-parasitized bees for each pollen diet (<i>p</i> < 0.05, Mann-Whitney U tests). Boxes show 1st and 3rd interquartile range with line denoting median. Whiskers encompass 90% of the individuals, beyond which each outliers are represented by circles.</p

Effect of pollen diet and <i>Nosema ceranae</i> infection on gut alkaline phosphatase.

<p>Box plots are shown for 3 pools of 3 bees/replicate (<i>n</i> = 9 replicates giving 81 bees total/pollen diet). Different letters denote significant differences between pollen diets in non-parasitized (white box plots) or <i>Nosema</i>-parasitized bees (grey box plots) (<i>p</i> < 0.05, Kruskal-Wallis and Dunn’s multiple comparison tests) and * indicate significant differences between parasitized and non-parasitized bees for each pollen diet (<i>p</i> < 0.05, Mann-Whitney U tests). Boxes show 1st and 3rd interquartile range with line denoting median. Whiskers encompass 90% of the individuals, beyond which each outliers are represented by circles.</p

Effects of pollen diet and <i>Nosema ceranae</i> infection on glutathione S-transferase.

<p>The enzyme activity was assessed in (A) the guts and (B) the heads of bees. Box plots are shown for 3 pools of 3 bees/replicate (<i>n</i> = 9 replicates giving 81 bees total/pollen diet). Different letters denote significant differences between pollen diets in non-parasitized (white box plots) or <i>Nosema</i>-parasitized bees (grey box plots) (<i>p</i> < 0.05, Kruskal-Wallis and Dunn’s multiple comparison tests) and * indicate significant differences between parasitized and non-parasitized bees for each pollen diet (<i>p</i> < 0.05, Mann-Whitney U tests). Boxes show 1st and 3rd interquartile range with line denoting median. Whiskers encompass 90% of the individuals, beyond which each outliers are represented by circles.</p