Nathalie Gauthier

Spatial and host-plant partitioning between coexisting Bemisia tabaci cryptic species in Tunisia

The whitefly Bemisia tabaci is a species complex including at least 24 morphologically indistinguishable species among which the Mediterranean (Med) and Middle East-Asia Minor I (MEAMI) species containing the biotypes commonly known as Q and B, respectively. These B and Q biotypes (hereafter referred to as MEAMI and Med species) are the most invasive agricultural pests of the B. tabaci complex worldwide. The spread of MEAMI and more recently of Med species into regions already invaded by other B. tabaci populations has been frequently seen to lead to their displacement by Med species. In Tunisia, in contrast to usual observations in the Mediterranean basin, Med and MEAMI species have been seen to co-occur in the main crop producing regions. Based on fine population genetics and field spatial distribution analyses, we found that the co-existence of these two interacting species was based on habitat partitioning including spatial and host-plant partitioning. Although they co-occurred at larger spatial scales, they excluded one another at sample scale. We observed neither spatial overlapping nor hybridization between MEAMI and Med B. tabaci. Vegetable crops were the main hosts for MEAMI specimens while 99.1% of the B. tabaci collected on the ornamental, Lantana camara, were Med specimens. Different patterns of genetic diversity were observed between the two species, as well as among Med specimens sampled on the ornamental versus vegetables, with the highest genetic diversity found in Med B. tabaci sampled on L. camara. These findings lead us to focus our discussion on the role played by lantana, human pressure, and competition, in the spatial and genetic patterns observed in the whitefly B. tabaci.

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.

First report of the Q biotype of Bemisia tabaci in Argentina and Uruguay

Bemisia tabaci adults were collected from pepper and melon at different commercial production greenhouses in Argentina and Uruguay. The biotype status of adults was then established using cytochrome oxidase I gene (mtCOI) as molecular marker. Only the Q biotype was found on all plants sampled. This is the first report of the Q biotype in Argentina and Uruguay.

Permanent Genetic Resources added to Molecular Ecology Resources Database 1 April 2012 - 31 May 2012: PERMANENT GENETIC RESOURCES NOTE

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.

Regional co-occurrence between distinct Bemisia tabaci species in Tunisia with new insights into the role of host plants

Among the Bemisia tabaci (Hemiptera: Aleyrodidae) species complex, the Middle East–Asia Minor I (MEAMI) and the Mediterranean (Med) species are the most invasive and widespread agricultural pests worldwide. Currently, only Tunisia and a few other countries are reported to still “host” these two competing species. The objective was thus to improve our knowledge on the factors, particularly the host plant, which contribute to this unusual situation. To that end, we analyzed 47 samples collected from protected and outdoor plants (ten vegetables and ornamentals) in the two main crop-producing regions of Tunisia to (i) better document the co-occurrence of several B. tabaci species and populations, and (ii) confirm the role of the host plant in the distribution pattern of each species. B. tabaci specimens were identified using at least two molecular diagnostic tests. Taken together, the tests confirmed the equivalent prevalence of Med and MEAMI species and, for the first time, the presence of some Sub-Saharan Africa 2 B. tabaci, in Tunisia. The regional co-occurrence between Med and MEAM1 was based on spatial and host-plant partitioning. Our results indicate that Med species are closely associated with ornamentals and MEAM1 with vegetables. Med displayed a higher level of genetic diversity than MEAM1, and another Med specimen characterized by a mtCOI haplotype which perfectly matched the ancestral Gennadius specimen was discovered. The role of host plant type and possible associated factors in the distribution patterns of MEAM1 and Med is discussed in the context of the co-occurrence of cryptic species.

Agroecosystems shape population genetic structure of the greenhouse whitefly in Northern and Southern Europe

BackgroundTo predict further invasions of pests it is important to understand what factors contribute to the genetic structure of their populations. Cosmopolitan pest species are ideal for studying how different agroecosystems affect population genetic structure within a species at different climatic extremes. We undertook the first population genetic study of the greenhouse whitefly (Trialeurodes vaporariorum), a cosmopolitan invasive herbivore, and examined the genetic structure of this species in Northern and Southern Europe. In Finland, cold temperatures limit whiteflies to greenhouses and prevent them from overwintering in nature, and in Greece, milder temperatures allow whiteflies to inhabit both fields and greenhouses year round, providing a greater potential for connectivity among populations. Using nine microsatellite markers, we genotyped 1274 T. vaporariorum females collected from 18 greenhouses in Finland and eight greenhouses as well as eight fields in Greece.ResultsPopulations from Finland were less diverse than those from Greece, suggesting that Greek populations are larger and subjected to fewer bottlenecks. Moreover, there was significant population genetic structure in both countries that was explained by different factors. Habitat (field vs. greenhouse) together with longitude explained genetic structure in Greece, whereas in Finland, genetic structure was explained by host plant species. Furthermore, there was no temporal genetic structure among populations in Finland, suggesting that year-round populations are able to persist in greenhouses.ConclusionsTaken together our results show that greenhouse agroecosystems can limit gene flow among populations in both climate zones. Fragmented populations in greenhouses could allow for efficient pest management. However, pest persistence in both climate zones, coupled with increasing opportunities for naturalization in temperate latitudes due to climate change, highlight challenges for the management of cosmopolitan pests in Northern and Southern Europe.

First report of the Sub-Saharan Africa 2 species of the Bemisia tabaci complex in the Southern France

An extensive survey was conducted in the major crop producing regions of France, Spain, Greece, Tunisia and Morocco from 2003 to 2010, to determine the geographical distribution of the Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) complex in the Mediterranean basin. Based on diagnostic and highly discriminatory molecular markers (mitochondrial cytochrome oxidase I, COI, gene sequences and nuclear microsatellites) and multiple complementary genetic diagnostic approaches including population assignment and phylogenetic reconstruction, the two worldwide invasive members of the complex, Med and MEAM1 species, were shown to be present, with Med being the most prevalent. In addition, the sub-Saharan Africa 2 (SSA2) species was, for the first time, reported in Southern France in 2007 on soybean and nightshade either alone or in sympatry with B. tabaci populations of the middle-eastern Mediterranean group (i.e., Q2 Med). This first occurrence of SSA2 in France, although detected in a relatively small area illustrates the capacity of multiple members of the B. tabaci complex to invade new regions, and emphasizes the possible risk caused by the entry of a new species, such as the SSA2 species, in the Mediterranean area.

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.