Interaction of a Densovirus with Glycans of the Peritrophic Matrix Mediates Oral Infection of the Lepidopteran Pest Spodoptera frugiperda.

The success of oral infection by viruses depends on their capacity to overcome the gut epithelial barrier of their host to crossing over apical, mucous extracellular matrices. As orally transmitted viruses, densoviruses, are also challenged by the complexity of the insect gut barriers, more specifically by the chitinous peritrophic matrix, that lines and protects the midgut epithelium; how capsids stick to and cross these barriers to reach their final cell destination where replication goes has been poorly studied in insects. Here, we analyzed the early interaction of the Junonia coenia densovirus (JcDV) with the midgut barriers of caterpillars from the pest Spodoptera frugiperda. Using combination of imaging, biochemical, proteomic and transcriptomic analyses, we examined in vitro, ex vivo and in vivo the early interaction of the capsids with the peritrophic matrix and the consequence of early oral infection on the overall gut function. We show that the JcDV particle rapidly adheres to the peritrophic matrix through interaction with different glycans including chitin and glycoproteins, and that these interactions are necessary for oral infection. Proteomic analyses of JcDV binding proteins of the peritrophic matrix revealed mucins and non-mucins proteins including enzymes already known to act as receptors for several insect pathogens. In addition, we show that JcDV early infection results in an arrest of N-Acetylglucosamine secretion and a disruption in the integrity of the peritrophic matrix, which may help viral particles to pass through. Finally, JcDV early infection induces changes in midgut genes expression favoring an increased metabolism including an increased translational activity. These dysregulations probably participate to the overall dysfunction of the gut barrier in the early steps of viral pathogenesis. A better understanding of early steps of densovirus infection process is crucial to build biocontrol strategies against major insect pests.

Microsatellite variability in the entomopathogenic fungus Paecilomyces fumosoroseus: genetic diversity and population structure.

The hyphomycete Paecilomyces fumosoroseus (Pfr) is a geographically widespread fungus capable of infecting various insect hosts. The fungus has been used for the biological control of several important insect pests of agriculture. However knowledge of the fungus' genetic diversity and population structure is required for its sustainable use as a biological control agent. We investigated length and sequence polymorphisms of nine microsatellite loci for 33 Pfr accessions sampled from various host species and geographical locations, and our results reveal complex mutational processes for these molecular markers. Only Pfr isolates from Bemisia tabaci were amplified successfully, indicating the existence of Pfr genotypes specifically associated with B. tabaci. Genetic relationships among the 25 Pfr isolates from B. tabaci were inferred from allelic variability data at eight microsatellite loci that were polymorphic and subsequently from sequence data from the flanking regions of three selected loci. Maximum parsimony and neighbor joining analyses partitioned Pfr genetic diversity in two major lineages. One lineage included genotypes from the B-biotype of B. tabaci distributed across the Americas and was strongly supported in both analyses. Another lineage was distributed across Asia and consisted of four distinct clusters. Allele size homoplasy was found at the three microsatellite loci. We obtained better discrimination and resolution of the relationships among isolates with sequence data, although not all isolates could be typed. Thus sequencing of microsatellite flanking regions and repeats is a promising approach for the identification of Pfr isolates that specifically infect certain B. tabaci biotypes and phylogeographic studies.

Population genetic structure of the biological control agent Macrolophus pygmaeus in Mediterranean agroecosystems.

Biological control of agricultural pests relies on knowledge of agroecosystem functionality, particularly when affected by the use of mass-produced biological agents. Incorporating pre- and/or post-release information such as genetic diversity and structure on these agents using molecular-based approaches could advance our knowledge of how they perform in agroecosystems. We evaluated the population genetics of Macrolophus pygmaeus, the most widely used predatory mirid against many arthropod pests of greenhouse crops in the Mediterranean region, using the mitochondrial Cytb sequence and microsatellite data, and population genetics and phylogeny approaches. We investigated commercially mass-produced insects (i.e., commercial insects either mass-reared in the laboratory for many generations, or purchased by farmers and released in the greenhouses) and "wild" insects (i.e., that occur naturally outside or are collected in nature for release in the greenhouses). The mirids were mainly collected in agroecosystems in which solanaceous plants are grown in northern Spain, southern France and Greece. Both molecular markers and approaches distinguished 2 genetically differentiated populations. The less genetically diverse population, hereafter named the "commercial" strain included all individuals from laboratory mass-rearings and most releases of commercially bred individuals. The most genetically diverse population mainly comprised individuals originating from noncultivated environments, or from releases of "wild" individuals. Rare examples of hybridization between M. pygmaeus from the 2 populations were observed and asymmetric gene flow was revealed. These findings provide new insights into what happens to M. pygmaeus released in the agroecosystems we studied, and show that it is possible to monitor some commercial strains.

Genetic structure of Bemisia tabaci Med populations from home-range countries, inferred by nuclear and cytoplasmic markers: impact on the distribution of the insecticide resistance genes.

BACKGROUND: Insecticide resistance management in Bemisia tabaci is one of the main issues facing agricultural production today. An extensive survey was undertaken in five Mediterranean countries to examine the resistance status of Med B. tabaci species in its range of geographic origin and the relationship between population genetic structure and the distribution of resistance genes. The investigation combined molecular diagnostic tests, sequence and microsatellite polymorphism studies and monitoring of endosymbionts. RESULTS: High frequencies of pyrethroid (L925I and T929V, VGSC gene) and organophosphate (F331W, ace1 gene) resistance mutations were found in France, Spain and Greece, but not in Morocco or Tunisia. Sequence analyses of the COI gene delineated two closely related mitochondrial groups (Q1 and Q2), which were found either sympatrically (Spain) or separately (France). Only Q1 was observed in Greece, Morocco and Tunisia. Bayesian analyses based on microsatellite loci revealed three geographically delineated genetic groups (France, Spain, Morocco/Greece/Tunisia) and high levels of genetic differentiation even between neighbouring samples. Evidence was also found for hybridisation and asymmetrical gene flow between Q1 and Q2. CONCLUSIONS: Med B. tabaci is more diverse and structured than reported so far. On a large geographic scale, resistance is affected by population genetic structure, whereas on a local scale, agricultural practices appear to play a major role.

Permanent genetic resources added to molecular ecology resources database 1 April 2012 - 31 May 2012.

This article documents the addition of 123 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Brenthis ino, Cichla orinocensis, Cichla temensis, Epinephelus striatus, Gobio gobio, Liocarcinus depurator, Macrolophus pygmaeus, Monilinia vaccinii-corymbosi, Pelochelys cantorii, Philotrypesis josephi, Romanogobio vladykovi, Takydromus luyeanus and Takydromus viridipunctatus. These loci were cross-tested on the following species: Cichla intermedia, Cichla ocellaris, Cichla pinima, Epinephelus acanthistius, Gobio carpathicus, Gobio obtusirostris, Gobio sp. 1, Gobio volgensis, Macrolophus costalis, Macrolophus melanotoma, Macrolophus pygmaeus, Romanogobio albipinnatus, Romanogobio banaticus, Romanogobio belingi, Romanogobio kesslerii, Romanogobio parvus, Romanogobio pentatrichus, Romanogobio uranoscopus, Takydromus formosanus, Takydromus hsuehshanesis and Takydromus stejnegeri.