A PCR-based method for estimating parasitism rates in the olive fly parasitoids Psyttalia concolor and P. lounsburyi (Hymenoptera: Braconidae)

International audienceSeveral parasitoids of the genus Psyttalia have been repeatedly introduced as biological control agents against the principal pest of olive, the fly Bactrocera oleae. However, few of the parasitoids released have become established and proved effective against B. oleae. It may however still be possible to find effective biological control agents adapted to local environmental conditions among the highly diverse Psyttalia species and populations infesting B. oleae worldwide. For this purpose, we have developed a rapid, sensitive molecular method based on the polymerase chain reaction (PCR) for estimating and comparing the parasitism success of Psyttalia parasitoids through the detection of eggs and larvae within the host. This method was tested and shown to be appropriate for two Psyttalia species (Psyttalia concolor and Psyttalia lounsburyi). The possible detection of DNA was also demonstrated for several populations of these species and for other Psyttalia species, namely Psyttalia humilis and Psyttalia ponerophaga. For P. concolor and P. lounsburyi, a strong correlation was observed between the parasitism rates estimated by PCR, host larva dissection and counts of emerging parasitoids. No significant difference was found between the rates of parasitism estimated by host larva dissection and PCR, whereas the rates of parasitism estimated by PCR were significantly higher than those estimated from emergence, suggesting occurrence of mortality during the parasitoid development. This PCR method is thus highly reliable and provides an objective criterion for estimating the efficacy of biological control agent candidates from diverse taxa and populations of Psyttalia. ⇑ Corresponding author

Rapid and dfferential evolution of the venom composition of a parasitoid wasp depending on the host strain

Abstract: Parasitoid wasps rely primarily on venom to suppress the immune response and regulatethe physiology of their host. Intraspecific variability of venom protein composition has beendocumented in some species, but its evolutionary potential is poorly understood. We performed anexperimental evolution initiated with the crosses of two lines of Leptopilina boulardi of differentvenom composition to generate variability and create new combinations of venom factors. Theoffspring were maintained for 10 generations on two strains of Drosophila melanogaster differing inresistance/susceptibility to the parental parasitoid lines. The venom composition of individuals wascharacterized by a semi-automatic analysis of 1D SDS-PAGE electrophoresis protein profiles whoseaccuracy was checked by Western blot analysis of well-characterized venom proteins. Results madeevident a rapid and differential evolution of the venom composition on both hosts and showed thatthe proteins beneficial on one host can be costly on the other. Overall, we demonstrated the capacityof rapid evolution of the venom composition in parasitoid wasps, important regulators of arthropodpopulations, suggesting a potential for adaptation to new hosts. Our approach also proved relevantin identifying, among the diversity of venom proteins, those possibly involved in parasitism successand whose role deserves to be deepened

Variability of venom components in immune suppressive parasitoid wasps: From a phylogenetic to a population approach

International audienceEndoparasitoid wasps develop at the expense of other insects, leading to their death. Eggs deposited inside the host body induce an immune response, which results in the formation of a melanized cellular capsule around the egg. To evade or counteract this response, endoparasitoids have evolved different strategies, the most often reported being injection into the host of immunosuppressive factors, notably venom proteins, along with the egg. The analysis of venom components has been performed independently in species of different taxa, but the present picture is far from complete. Intriguingly, the question of the level of venom variability inside species has been neglected, although it may partly determine the potential for parasitoid adaptation. Here, we present a short review of our present knowledge of venom components in endoparasitoids, as well as of the only well-known example of intraspecific variability in a venom immune suppressive protein being responsible for variation in parasitoid virulence. We then present data evidencing inter-individual variation of venom protein profiles, using a gel electrophoresis approach, both in laboratory strains and field populations of a figitid and a braconid species. Whether occurrence of such variability may permit a selection of parasitoid venom components driven by the host remains to be tested, notably in the context of the production and use of biological control auxiliaries

The effect of mating system on invasiveness: some genetic load may be advantageous when invading new environments

The role of adaptation in determining invasion success has been acknowledged recently, notably through the accumulation of case studies of rapid evolution during bioinvasions. Despite this growing body of empirical evidence, there is still a need to develop the theoretical background of invasions with adaptation.Specifically,thei mpact of mating system on the dynamics of adaptation during invasion of a new environment remains only partially understood. Here, we analyze a simulation demo-genetic model of bioinvasion accounting for partial asexuality rates. We simulate two levels of recurrent immigration from a source population at mutation–drift–selection equilibrium to a new empty environment with a different adaptive landscape (black-holesink). Adaptation relies on a quantitative trait coded explicitly by10 lociunder mutation, selection and genetic drift. Using this model, we confirm previous results on the positive effects on invasiveness of migration, mutation and similarity of local phenotypic optima. We further show how the invasion dynamics of the introduced population is affected by the rate of asexuality. Purely asexual species have lower invasion success in terms of probability and time to invasion than species with other matingsystems. Among species with mixed mating systems, the greatest invasiveness is observed for species with high asexual rates. We suggest that this pattern is due to inflated genetic variance in the source population through the Hill-Robertson effect (i.e., clonal interference). An interesting consequence is that species with the highest genetic load in their source environment have greatest invasiveness in the new environment

Nonrandom associations of maternally transmitted symbionts in insects: The roles of drift versus biased cotransmission and selection

International audienc

Variation intra et interspécifique du venin chez un auxiliaire de lutte biologique

National audienc

Rapid and differential evolution of the venom composition of a parasitoid wasp depending on the host strain

Parasitoid wasps rely primarily on venom to suppress the immune response and regulate the physiology of their host. Intraspecific variability of venom protein composition has been documented in some species, but its evolutionary potential is poorly understood. We performed an experimental evolution initiated with crosses of two lines of Leptopilina boulardi of different venom composition to generate variability and create new combinations of venom factors. The offspring were maintained for 10 generations on two strains of Drosophila melanogaster differing in resistance / susceptibility to the parasitoid lines. The venom composition of individuals was characterized by a semi-automatic analysis of 1D SDS-PAGE protein profiles whose accuracy was checked by Western blot analysis of well-characterized venom proteins. Results evidenced a rapid and differential evolution of the venom composition on both hosts and showed that the proteins beneficial on one host can be costly on the other. Overall, we demonstrated the capacity of rapid evolution of the venom composition in parasitoid wasps, important regulators of arthropod populations, suggesting a potential for adaptation to new hosts. Our approach also proved relevant in identifying, among the diversity of venom proteins, those possibly involved in parasitism success and whose role deserves to be deepened

Effets de l'élevage sur un hôte de substitution chez les parasitoïdes Psyttalia lounsburyi et P. concolor utilisés en lutte biologique: Une approche de vénomique

National audienceLes endoparasitoïdes pondent à l ’ intérieur d 'un insecte hôte dans lequel ils se développent, entraînant sa mort. Leur succès reproducteur dépend donc de leur capacité à contrôler l'immunité et la physiologie de l'hôte (Dupas et al. 2003). Les stratégies utilisées font notamment appel à l'injection de facteurs de virulence lors de la ponte, la plupart étant des protéines contenues dans le venin (Pennachio et Strand, 2006) qui peuvent être étudiées par des approches dites de "vénomique". Les parasitoïdes sont souvent utilisés en lutte biologique, mais leur qualité au moment des lâchés sur le terrain, lorsqu'elle est évaluée, est généralement étudiée via des mesures de traits phénotypiques peu pertinents et des outils moléculaires d'estimation de la diversité génétique, sans lien avec les traits précédents. Par exemple, leur production s'effectue souvent sur un hôte de substitution. L’ impact de ce changement d'hôte n'est pas ou peu connu. Il pourrait être une force sélective sur les stratégies de virulence de l’auxiliaire. Il est donc susceptible d’induire une maladaptation à l’hôte naturel, c'est-à- dire la cible finale de la lutte biologique. Les démonstrations expérimentales de tels phénomènes sont très rares. L'étude est menée pour 2 espèces de parasitoïde, Psyttalia lounsburyi et concolor , utilisés pour lutter contre la mouche de l ’ olive Bactrocera oleae . Les souches parasitoïdes sont élevées au laboratoire sur l'hôte de substitution Ceratitis capitata (mouche des fruits) que seul P. concolor est naturellement capable de parasiter. L'étude consiste à caractériser des protéines du venin et leur variation inter-espèce, inter-souche et inter-individu et ensuite à tester leur évolution en réponse au changement d’hôte. Actuellement, 5 souches sont maintenues au laboratoire sur C. capitata : une souche de P. concolor depuis 13 générations, 2 souches de P. lounsburyi depuis environ 100 générations (une Sud Africaine, une Kényane, initialement fortement différenciées (F ST = 0,4). Par ailleurs, les populations de P. lounsburyi ont très récemment été ré-échantillonnée sur les sites précédemment échantillonnés il y a 7 ans. Ces souches permettront d'étudier l'évolution du venin et du succès parasitaire dans les conditions d'élevage, suite au changement d'hôte

Variability and evolution of the venom of two biological control agents from the genus Psyttalia

International audienc

Comparative venomics of Psyttalia lounsburyi and P. concolor, two olive fruit fly parasitoids: a hypothetical role for a GH1 β-glucosidase

International audienceVenom composition of parasitoid wasps attracts increasing interest - notably molecules ensuring parasitism success on arthropod pests - but its variation within and among taxa is not yet understood. We have identified here the main venom proteins of two braconid wasps, Psyttalia lounsburyi (two strains from South Africa and Kenya) and P. concolor, olive fruit fly parasitoids that differ in host range. Among the shared abundant proteins, we found a GH1 β-glucosidase and a family of leucine-rich repeat (LRR) proteins. Olive is extremely rich in glycoside compounds that are hydrolyzed by β-glucosidases into defensive toxic products in response to phytophagous insect attacks. Assuming that Psyttalia host larvae sequester ingested glycosides, the injected venom GH1 β-glucosidase could induce the release of toxic compounds, thus participating in parasitism success by weakening the host. Venom LRR proteins are similar to truncated Toll-like receptors and may possibly scavenge the host immunity. The abundance of one of these LRR proteins in the venom of only one of the two P. lounsburyi strains evidences intraspecific variation in venom composition. Altogether, venom intra- and inter-specific variation in Psyttalia spp. were much lower than previously reported in the Leptopilina genus (Figitidae), suggesting it might depend upon the parasitoid taxa