Convergent Use of RhoGAP Toxins by Eukaryotic Parasites and Bacterial Pathogens

Inactivation of host Rho GTPases is a widespread strategy employed by bacterial pathogens to manipulate mammalian cellular functions and avoid immune defenses. Some bacterial toxins mimic eukaryotic Rho GTPase-activating proteins (GAPs) to inactivate mammalian GTPases, probably as a result of evolutionary convergence. An intriguing question remains whether eukaryotic pathogens or parasites may use endogenous GAPs as immune-suppressive toxins to target the same key genes as bacterial pathogens. Interestingly, a RhoGAP domain–containing protein, LbGAP, was recently characterized from the parasitoid wasp Leptopilina boulardi, and shown to protect parasitoid eggs from the immune response of Drosophila host larvae. We demonstrate here that LbGAP has structural characteristics of eukaryotic RhoGAPs but that it acts similarly to bacterial RhoGAP toxins in mammals. First, we show by immunocytochemistry that LbGAP enters Drosophila immune cells, plasmatocytes and lamellocytes, and that morphological changes in lamellocytes are correlated with the quantity of LbGAP they contain. Demonstration that LbGAP displays a GAP activity and specifically interacts with the active, GTP-bound form of the two Drosophila Rho GTPases Rac1 and Rac2, both required for successful encapsulation of Leptopilina eggs, was then achieved using biochemical tests, yeast two-hybrid analysis, and GST pull-down assays. In addition, we show that the overall structure of LbGAP is similar to that of eukaryotic RhoGAP domains, and we identify distinct residues involved in its interaction with Rac GTPases. Altogether, these results show that eukaryotic parasites can use endogenous RhoGAPs as virulence factors and that despite their differences in sequence and structure, eukaryotic and bacterial RhoGAP toxins are similarly used to target the same immune pathways in insects and mammals

Parasitoids (Hymenoptera) of Mealybug Pests (Hemiptera: Pseudococcidae) from Southern Brazil: Molecular and Morphological Characterization

Parasitoids of three mealybug pests (Hemiptera: Pseudococcidae), Planococcus ficus (Signoret), Pseudococcus sociabilis Hambleton, and Pseudococcus viburni (Signoret) have been identified for the first time in Brazil. Mealybugs were collected in fruit-growing areas along southern Brazil during 2013-2016. An integrative approach, combining morphological and molecular methods, was used to identify the Brazilian parasitoids to the species level. Fifteen species were recorded, including 14 primary parasitoids belonging to Encyrtidae and Platygastridae and a single secondary parasitoid species belonging to Signiphoridae. The encyrtid parasitoids Acerophagus flavidulus (Brethes), Anagyrus calyxtoi Noyes and Zaplatycerus sp., and the signiphorid secondary parasitoid Chartocerus axillaris De Santis are reported for the first time in Brazil.Centro de Estudios Parasitológicos y de VectoresCentro de Investigación en Sanidad Vegeta

Guiding Classical Biological Control of an Invasive Mealybug Using Integrative Taxonomy

The analysed sequences were deposited in Genbank under accession numbers KP771926-KP771972. Mealybug slides are available at the Polytechnic University of Valencia (Valencia, Spain). Parasitoid slides are deposited at Università degli Studi di Napoli Federico II (Portici, Italy).[EN] Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae) is a mealybug of Southern African origin that has recently been introduced into Eastern Spain. It causes severe distortions on young citrus fruits and represents a growing threat to Mediterranean citrus production. So far, biological control has proven unsatisfactory due to the absence of efficient natural enemies in Spain. Hence, the management of this pest currently relies only on chemical control. The introduction of natural enemies of D. aberiae from the native area of the pest represents a sustainable and economically viable alternative to reduce the risks linked to pesticide applications. Since biological control of mealybugs has been traditionally challenged by taxonomic misidentification, an intensive survey of Delottococcus spp. and their associated parasitoids in South Africa was required as a first step towards a classical biological control programme. Combining morphological and molecular characterization (integrative taxonomy) a total of nine mealybug species were identified in this study, including three species of Delottococcus. Different populations of D. aberiae were found on wild olive trees, in citrus orchards and on plants of Chrysanthemoides monilifera, showing intra-specific divergences according to their host plants. Interestingly, the invasive mealybug populations from Spanish orchards clustered together with the population on citrus from Limpopo Province (South Africa), sharing COI haplotypes. This result pointed to an optimum location to collect natural enemies against the invasive mealybug. A total of 14 parasitoid species were recovered from Delottococcus spp. and identified to genus and species level, by integrating morphological and molecular data. A parasitoid belonging to the genus Anagyrus, collected from D. aberiae in citrus orchards in Limpopo, is proposed here as a good biological control agent to be introduced into Spain.This work was supported by the European Union Seventh Framework Programme FP7-IRSES #269196 "IPRABIO" and FP7-IAPP #324475 "COLBICS" and FP7-IRSES #612566 "BIOMODICS". The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.Beltrà Ivars, A.; Addison, P.; Ávalos Masó, JA.; Crochard, D.; García Mari, F.; Guerrieri, E.; Giliomee, JH.... (2015). Guiding Classical Biological Control of an Invasive Mealybug Using Integrative Taxonomy. PLoS ONE. 10(6):1-14. https://doi.org/10.1371/journal.pone.0128685S11410

Temporal autocorrelation in host density increases establishment success of parasitoids in an experimental system

International audienceEnvironmental variation is classically expected to affect negatively population growth and to increase extinction risk, and it has been identified as a major determinant of establishment failures in the field. Yet, recent theoretical investigations have shown that the structure of environmental variation and more precisely the presence of positive temporal autocorrelation might alter this prediction. This is particularly likely to affect the establishment dynamics of biological control agents in the field, as host–parasitoid interactions are expected to induce temporal autocorrelation in host abundance. In the case where parasitoid populations display overcompensatory dynamics, the presence of such positive temporal autocorrelation should increase their establishment success in a variable environment. We tested this prediction in laboratory microcosms by introducing parasitoids to hosts whose abundances were manipulated to simulate uncorrelated or positively autocorrelated variations in carrying capacity. We found that environmental variability decreased population size and increased parasitoid population variance, which is classically expected to extinction risk. However, although exposed to significant environmental variation, we found that parasitoid populations experiencing positive temporal autocorrelation in host abundance were more likely to persist than populations exposed to uncorrelated variation. These results confirm that environmental variation is a key determinant of extinction dynamics that can have counterintuitive effects depending on its autocorrelation structure

Diversification of MIF immune regulators in aphids: link with agonistic and antagonistic interactions

International audienceBackground: The widespread use of genome sequencing provided evidences for the high degree of conservation in innate immunity signalling pathways across animal phyla. However, the functioning and evolutionary history of immune-related genes remains unknown for most invertebrate species. A striking observation coming from the analysis of the pea aphid Acyrthosiphon pisum genome is the absence of important conserved genes known to be involved in the antimicrobial responses of other insects. This reduction in antibacterial immune defences is thought to be related to their long-term association with beneficial symbiotic bacteria and to facilitate symbiont maintenance. An additional possibility to avoid elimination of mutualistic symbionts is a fine-tuning of the host immune response. To explore this hypothesis we investigated the existence and potential involvement of immune regulators in aphid agonistic and antagonistic interactions. Results: In contrast to the limited antibacterial arsenal, we showed that the pea aphid Acyrthosiphon pisum expresses 5 members of Macrophage Migration Inhibitory Factors (ApMIF), known to be key regulators of the innate immune response. In silico searches for MIF members in insect genomes followed by phylogenetic reconstruction suggest that evolution of MIF genes in hemipteran species has been shaped both by differential losses and serial duplications, raising the question of the functional importance of these genes in aphid immune responses. Expression analyses of ApMIFs revealed reduced expression levels in the presence, or during the establishment of secondary symbionts. By contrast, ApMIFs expression levels significantly increased upon challenge with a parasitoid or a Gram-negative bacteria. This increased expression in the presence of a pathogen/parasitoid was reduced or missing, in the presence of facultative symbiotic bacteria. Conclusions: This work provides evidence that while aphid's antibacterial arsenal is reduced, other immune genes widely absent from insect genomes are present, diversified and differentially regulated during antagonistic or agonistic interactions

European bridgehead effect in the worldwide invasion of the obscure mealybug

Identifying the main routes followed by an invasive species has significant management implications and may help to understand its colonization process. The obscure mealybug, Pseudococcus viburni (Signoret, 1875), is an important agricultural pest native to South America that infests fruit crops worldwide. The genetic diversity and structure of P. viburni samples collected around the globe was investigated here, and the most likely invasion routes were inferred using state-of-the-art population genetic methods. The results obtained include: (1) identification of low intrapopulation genetic diversity (mean number of alleles per locus below 4 and heterozygosity below 50%) and high genetic differentation among populations (average FST = 0.29); (2) strong evidence of an initial colonization from South America towards Europe and secondary introductions from Europe towards other continents, (3) evidence of population structure within Europe and, (4) support for 26 introductions from North America and Europe to South Africa. These results improve our understand- 28 ing of the worldwide distribution and invasion path-ways of P. viburni and suggest further exploring South America as the best source for potential biological control agents.MCG Correa received financial support from Chile CONICYT Doctoral fellowship #21110864 and CONICYT ‘‘Tesis en la Industria’’ #7812110011 and Fondecyt #1170943. This research was also funded by the European Union (FP7 grants KBBE ‘‘PURE’’ #265865, Marie-Curie IRSES ‘‘IPRABIO’’ #269196, and Marie-Curie IAPP ‘‘COLBICS’’ #324475), by the Grant CHALLENGEN (CTM2013-48163) from the Spanish Government and a post-doctoral contract funded by the Beatriu de Pinos Programme of the Generalitat de Catalunya (2014-BPB-00038).Peer reviewe

Investigating Biological Control Agents for Controlling Invasive Populations of the Mealybug Pseudococcus comstocki in France

WOS: 000378865200032PubMed ID: 27362639Pseudococcus comstocki (Hemiptera: Pseudococcidae) is a mealybug species native to Eastern Asia and present as an invasive pest in northern Italy and southern France since the start of the century. It infests apple and pear trees, grapevines and some ornamental trees. Biocontrol programmes against this pest proved successful in central Asia and North America in the second half of the 20th century. In this study, we investigated possible bio-control agents against P. comstocki, with the aim of developing a biocontrol programme in France. We carried out systematic DNA-barcoding at each step in the search for a specialist parasitoid. First we characterised the French target populations of P. comstocki. We then identified the parasitoids attacking P. comstocki in France. Finally, we searched for foreign mealybug populations identified a priori as P. comstocki and surveyed their hymenopteran parasitoids. Three mealybug species (P. comstocki, P. viburni and P. cryptus) were identified during the survey, together with at least 16 different parasitoid taxa. We selected candidate biological control agent populations for use against P. comstocki in France, from the species Allotropa burrelli (Hymenoptera: Platygastridae) and Acerophagus malinus (Hymenoptera: Encyrtidae). The coupling of molecular and morphological characterisation for both pests and natural enemies facilitated the programme development and the rejection of unsuitable or generalist parasitoids.French "Agence Nationale de la Recherche"French National Research Agency (ANR) [ANR-10-JCJC-1708 BICORAMICS]; EUEuropean Union (EU) [324475 COLBICS, 265865 PURE]; Turkey-France Cooperation grant CNRS-TUBITAK; INRA Plant Health and Environment DivisionInstitut National de la Recherche Agronomique (INRA)This work was funded by the French "Agence Nationale de la Recherche" (grant ANR-10-JCJC-1708 BICORAMICS), by the EU Seventh Framework Programme (grants Marie-Curie IAPP #324475 COLBICS and KBBE #265865 PURE), by a Turkey-France Cooperation grant CNRS-TUBITAK, and by the INRA Plant Health and Environment Division. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Does insecticide resistance alone account for the low genetic variability of asexually reproducing populations of the peach-potato aphid Myzus persicae ?

International audienceThe typical life cycle of aphids includes several parthenogenetic generations and a single sexual generation ( cyclical parthenogenesis), but some species or populations are totally asexual ( obligate parthenogenesis). Genetic variability is generally low in these asexually reproducing populations, that is, few genotypes are spread over large geographic areas. Both genetic drift and natural selection are often invoked to account for this low genetic variability. The peach-potato aphid, Myzus persicae, which encompasses both cyclical and obligate parthenogens, has developed several insecticide resistance mechanisms as a consequence of intense insecticide use since the 1950s. We collected asexually reproducing M. persicae from oilseed rape and examined genetic variability at eight microsatellite loci and three insecticide resistance genes to determine whether their genetic structure was driven by drift and/or selection. We identified only 16 multilocus microsatellite genotypes! among 255 individuals. One clone, which combined two insecticide resistance mechanisms, was frequently detected in all populations whatever their location over a large geographical area ( the northern half of France). These unexpected findings suggest that drift is not the unique cause of this low variability. Instead, the intensification of both insecticide treatments and oilseed rape cultivation may have favored a few genotypes. Thus, we propose that selective pressures resulting from human activities have considerably modified the genetic structure of M. persicae populations in northern France in a relatively short period of time