Macrogeographic population structuring in the cosmopolitan agricultural pest Bactrocera cucurbitae (Diptera:Tephritidae)

Background: The melon fly #Bactrocera cucurbitae# (Coquillett) is a major, highly polyphagous, agricultural pest abundant throughout the African continent, the islands of Indian Ocean, Asia, New Guinea, the Mariana Islands and Hawaii. This species attacks more than 125 plants including commercial crops such as pumpkin, cantaloupe, watermelon, squash, gourd, cucumber, tomato, eggplant and bean as well as soft fruits such as mango, orange, papaya and peach. Although the economic importance of B. cucurbitae is well documented, its large-scale (i.e. inter-regional) patterns of genetic structuring are poorly known. Hence, the current quarantine methods and management plans still rely on general assumptions concerning its intraspecific variation. The aim of this work was to 1) characterize the large-scale population structure of #Bactrocera cucurbitae#, 2) identify its geographic origin and 3) infer the dynamics of its range expansion. Methods: Individuals of #B. cucurbitae# were collected from 25 worldwide-distributed localities (n=570) and genotyped at 13 microsatellite loci specifically developed for this species. Genetic discontinuities among geographical regions were quantified through hierarchical analysis of molecular variance (AMOVA) and levels of population admixture were quantified through #Bayesian clustering# procedures. Results: Five main groups of populations were identified. These corresponded to populations from 1) the African continent, 2) La Réunion, 3) Central Asia, 4) East Asia and 5) Hawaii. The proportions of inter-regional assignments and the higher values of genetic diversity in populations from Pakistan, India and Bangladesh suggest that #B. cucurbitae# originated in Central Asia and expanded its range to East Asia and Hawaii on one hand and to Africa and the islands of the Indian Ocean on the other. A number of outliers (10-19 specimens according to different clustering algorithms) show high levels of admixture (Q>0.70) with populations from different regions and reveal complex patterns of inter-regional gene flow. Conclusions: Anthropogenic transport is the most plausible promoter of the large-scale dispersal of B. cucurbitae. The recent African invasions of B. cucurbitae were mainly due to the expansion of local populations while, hitherto, the introduction of individuals from geographically distant regions did not have a relevant role. The dynamics of the recent invasions, as well as the possible corridors to gene flow created by contemporary anthropogenic activities could provide a useful background to better evaluate invasion risks and establish priorities for the management of this cosmopolitan agricultural pest. (Texte intégral

Ecological plasticity and genetic diversity of the mango blossom gall midge, Procontarinia Mangiferae (Felt), in Reunion Island : O306F12 Ecology

Phytophagous insects that belong to the Cecidomyiidae family are among the most closely associated with their host plants. Phytophagous insects can specialize not only on a unique host plant but on particular parts of plants as well. Mango blossom gall midge, Procontarinia mangiferae, is a mango pest that causes damage to both inflorescences and leaves. The objectives of our study were to highlight the genetic diversity and ecological abilities of a monophagous gall midge and to evaluate the determinants of its genetic structure in subtropical Reunion Island. This study, carried out on an isolated island, is based on morphological and molecular data (mitochondrial DNA and microsatellites). Using mitochondrial COI gene sequences, polymorphism at 11 microsatellite loci and an extensive sampling of 27 populations at 17 sites, we tested the genetic differentiation between populations sampled on different mango organs, different mango cultivars and at different seasons. Our results showed that a single species, P. mangiferae, was present all year round at all of the sites sampled, regardless of climatic and cultural conditions, and that it fed on both inflorescences and young leaves. Moreover, our study highlighted the ecological plasticity of this species. However, unlike previous studies on other Cecidomyiidae species, the population genetic structure did not appear to be determined by the species' ability to feed on different organs of the same host plant, but rather by the geographical distribution of populations. (Résumé d'auteur

Life traits of Aedes mosquitoes as factors of arboviruses emergence : S1304TU01 Medical and Veterinary Entomology

Life traits of Aedes mosquitoes as factors of arboviruses emergence Among the >3500 mosquito species described in the world, only a few hundred are able to transmit arbovirus to human. For example, as less than 10 among 920 Aedes species effectively transmit dengue and Chikungunya viruses naturally. Based on recent field and experimental results particularly on Aedes albopictus, we will show the role and relative contribution of the different parameters of vector competence and vector capacity in shaping Aedes-arbovirus interactions and the resulting pathogen transmission dynamics and risk of emergence. These include mosquito life history traits and biology parameters such as population dynamics, longevity, trophic behavior, habitat preference, diapause, genetics, immunity and biotic interactions. The mechanisms and processes underlying the patterns observed in the field should be studied all the way, from molecules to individuals and populations, towards a better understanding of what makes a mosquito vector and how best to control it. (Résumé d'auteur

Interspecific interactions between a new invasive Tephritid fruit fly, Bactrocera dorsalis, and other resident species in an insular context

The impact of biological invasions of insects considered as pests have important negative impacts on the economy and the environment, particularly in insular ecosystems. Since the detection of one of the most harmful pest of fruit and vegetable crops, Bactrocera dorsalis, in April 2017, La R´eunion counts nowadays nine pests species of Tephritid fruit flies of economic importance. A biological control agent, the braconid wasp, Fopius arisanus, was initially introduced in La Reunion in 2003 to control another fruit fly of the same genus: the peach fruit fly, Bactrocera zonata. Bactrocera dorsalis, in its native area is the main host of this braconid wasp and will probably be able to parasitize it in La R´eunion. To understand the invasion process of B. dorsalis and the impact of this new introduced fruit fly on the community structure of the resident Tephritid species, and the parasitoid, F. arisanus, it is necessary to study the competition interactions. We first assessed the interspecific competition between Bactrocera dorsalis and four other fruit flies, Bactrocera zonata, C. capitata, C. quilicii and Ceratitis catoirii. Three of those fruit flies are successive invaders in La Reunion and one endemic species. We focused our study on the interference competition among pairs of adults, measuring the ability of a female to remove another one from a fruit for the laying behavior in controlled environments.The parasitoid preference for both sympatry species of genius Bactrocera were observed. On one hand, we observed the preference for eggs only and on the other hand, the preference for one particular species according to the host fruit in choice experiments

Biological invasions and endosymbiosis in Arthropods, a case study:Bemisia tabaci : S1403TH01 Invasive Species and Quarantine

Biological invasions are more and more frequent worldwide and understanding this process is a big issue. Invasive success depends on several traits permitting local adaptation. Among those traits, host-plant adaptations or demographic advantages are specific traits involving in some cases endosymbiosis. Intracellular prokaryotic association known as endosymbiosis is a well known-phenomenon which is present at least in 15% of all insects. Among the sap-sucking insects of the suborder Sternorrhyncha, psyllids, whiteflies, aphids, and mealybugs, an obligatory endosymbiont is even crucial to allow them to synthesise essential amino acids. Furthermore, other non obligatory endosymbionts, so-called secondary endosymbionts, are known to be linked to adaptive traits which can enhance invasiveness of their host. These biotic interactions will be discussed through several models and in particular the invasive whitefly Bemisia tabaci. Indeed, two biotypes (B and Q) or "genetic species" of B. tabaci have a tremendous invasive success worldwide since the 80ies. They harbor a wide range of endosymbionts, with potentially 6 secondary endosymbionts (according to biotypes): Cardinium, Arsenophonus, Hamiltonella, Rickettsia, Wolbachia and Fritschea and one obligatory Portiera aleyrodidarum. Recent studies showed significant links between reproductive manipulations (strong female bias, non random hybridization), large fitness benefits, better thermotolerance or transmission efficiency of begomoviruses according to the endosymbionts of their infected hosts. Most of the functions of those secondary endosymbionts are described in other models, and are largely unknown yet in B. tabaci. (Résumé d'auteur

Effects of intraspecific competition on the larval development and pupal weight of Dacini (Diptera : Tephritidae) infesting cucurbits in la Reunion

Background. In La Réunion, cucurbit crops suffer considerable damage due to fruit fly attacks. A complex of three species (The Melon fly, Bactrocera cucurbitae, The Ethiopian fly, Dacus ciliatus, and the Indian Ocean fruit fly, Dacus demmerezi) coexist in the island and can infest 16 different species of Cucurbitaceae. In order to develop sound and sustainable management methods for these pests, we need to know more about their behavior and ecology. The objective of this study is to clarify the interaction existing at larval stage, and particularly the competition which may occur between conspecific larvae in a same fruit. According to earlier studies, squash (Cucurbita pepo) was chosen for laboratory experiments because it is one of the most damaged cultivated cucurbit in La Réunion. Methods. To measure the effect of intraspecific competition on the survivorship rate of larvae and on the pupal mass, infestations of squash were carried out in the laboratory with L1 larvae of B. cucurbitae, D. ciliatus or D. demmerezi, obtained from lab rearing. Five levels of infestation were selected e.g. A) One larva (L1) for two grams of squash, B) One larva/1 g, C) Two larvae/1 g, D) Four larvae/1 g and E) Eight larvae/1 g. Each level was replicated five times. Four days after infestation, pupae were collected daily, weighed individually and grouped by weight classes in a same box and when they emerged, the adults were sexed. Results. Larvae of B. cucurbitae and D. demmerezi don't have the same response to an increase of intraspecific competition in a same fruit. Larvae of the first species show a good survivorship level (63% for level D) whereas larvae of D. demmerezi are more affected by a high level of competition (18% for level C). On the contrary, pupal weight of B. cucurbitae clearly decreases when the number of larvae increases in the fruit while pupal weight of D. demmerezi, does not seem to be affected by intraspecific competition. Conclusion. It seems that, in the complex of Dacini attacking cucurbits, the species do not have the same strategy regarding intraspecific competition. The larvae of B. cucurbitae are able to share resources and maintain a good survivorship finally giving more adults with low weight. Conversely, in D. demmerezi larval survivorship is decreased but the pupal weight of survivors remains high. Further studies will be needed on larval interspecific competition in this complex of fruit flies, in order to understand the performance of each species in situations of co-infestation. (Texte intégral

Isolation and characterization of 11 polymorphic microsatellite markers developed for Orthops palus(Heteroptera: Miridae)

Miridae (Hemiptera: Heteroptera: Cimicomorpha), or plant bugs, are one of the most diverse and species-rich families of insects. Most of them are phytophagous, but some are insect predators and used for biocontrol. Among this family, the mango bug, Orthops palus (Taylor 1947), is one of the most important pest of mango in Reunion Island. We developed 11 polymorphic microsatellite loci to study the population genetics of this pest species. The microsatellite markers were characterized by genotyping 78 field-collected insects sampled at different localities in Reunion Island. The number of alleles per locus ranged from 1 to 13 and heterozygosity levels ranged between 0.40 and 0.94. Several loci were not at Hardy–Weinberg equilibrium for the tested populations. These markers are the first to be developed for a species of the genus Orthops. (Résumé d'auteur

Heritability and evolvability of morphological traits of the honeybee Apis mellifera in tropical islands from the Mascarene archipelago

Before invoking evolutionary process to explain morphological divergences among insular popu-lations, estimation of morphological heratibility is essential. Indeed, phenotypic divergence between populations could be the result of either phenotypic plasticity or micro-evolutionary response to con-trasted environments. A given phenotypic trait could evolve only if it could be transmitted to the next generation, i.e. it has a genetic basis. Quantitative genetic studies typically permit to estimate this part of the genetic variance in the phenotypic variation of a trait, this ratio is the heritability. The islands and archipelagoes of the Southwest Indian Ocean (SOOI) present a great diversity of habitats. As evolutionary forces are exacerbated in islands, populations are expected to show large divergence between islands. Several studies have demonstrated genetic and morphological differentiation between populations of the honeybee Apis mellifera unicolor in the SOOI area. Hybridizations between African and European lines, introduced by beekeepers in La R´eunion and Mauritius, may explain a part of this differentiation pattern. Apis mellifera unicolor is an eusocial species with a polyandric and monogynic reproduction regime allowing quantitative genetic study to be conducted from wild populations. The objective of this study is to improve our understanding of the phenotypic differentiation of Apis mellif-era unicolor populations in Reunion and Mauritius through heritability estimates of two morphological characters. We will assess the heritability of the size of the wings and the length of the proboscis, two traits subjected to different evolutionary forces. We sampled 6 colonies in Reunion Island and 8 colonies in Mauritius, with 95 workers per colony. All individuals were genotyped using 8 microsatellite markers to reconstitute the pedigree of each colony. Morphometric measurements on individuals with known degrees of relatedness will allow to estimate the heritability of these traits, using a so-called animal model

Les populations de Cymbidium mosaic virus (CymMV, Protexvirus) sont divisées en deux haplogroupes en expansion

La diversité génétique du Cymbidium mosaic virus (CymMV, Flexiviridae) a été analysée à partir des séquences de deux gènes; RNA polymérase (RdRp, 37 séquences) et protéine de capside (CP, 85 séquences). La population de CymMV a une diversité nucléotidique modérée (p=0.053 et p=0.054 pour les gènes de RdRp et CP respectivement) mais est divisée en deux groupes phylogénétiques bien distincts (CymMV-A et CymMV-B). Ces deux groupes diffèrent également par le biais d'usage des codons et la structure secondaire des ARN. La majorité des différences nucléotidiques inter groupes est constituée de mutations silencieuses répartie uniformément le long des gènes étudiés. De ce fait, les séquences en acides aminés sont peu divergentes (86 à 100 % d'identité) et les deux groupes d'isolats indiscernables au niveau protéique. L'analyse des paramètres de génétique des populations montre que les deux gènes étudiés sont soumis à une forte pression de sélection (Ka/Ks = 0.009 et 0.040 pour les gènes RdRp et CP, respectivement) et suggère une forte expansion des populations de CymMV. Les isolats de CymMV qui infectent les orchidées cultivées paraissent donc avoir une origine duale et être issus de deux goulots d'étranglement. L'éventualité de propriétés biologiques différentes pour les deux groupes d'isolats reste à déterminer. (Résumé d'auteur