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Background Cassava whitefly outbreaks were initially reported in East and Central Africa cassava (Manihot esculenta Crantz) growing regions in the 1990’s and have now spread to other geographical locations, becoming a global pest severely affecting farmers and smallholder income. Whiteflies impact plant yield via feeding and vectoring cassava mosaic and brown streak viruses, making roots unsuitable for food or trading. Deployment of virus resistant varieties has had little impact on whitefly populations and therefore development of whitefly resistant varieties is also necessary as part of integrated pest management strategies. Suitable sources of whitefly resistance exist in germplasm collections that require further characterization to facilitate and assist breeding programs. Results In the present work, a hierarchical metabolomics approach has been employed to investigate the underlying biochemical mechanisms associated with whitefly resistance by comparing two naturally occurring accessions of cassava, one susceptible and one resistant to whitefly. Quantitative differences between genotypes detected at pre-infestation stages were consistently observed at each time point throughout the course of the whitefly infestation. This prevalent differential feature suggests that inherent genotypic differences override the response induced by the presence of whitefly and that they are directly linked with the phenotype observed. The most significant quantitative changes relating to whitefly susceptibility were linked to the phenylpropanoid super-pathway and its linked sub-pathways: monolignol, flavonoid and lignan biosynthesis. These findings suggest that the lignification process in the susceptible variety is less active, as the susceptible accession deposits less lignin and accumulates monolignol intermediates and derivatives thereof, differences that are maintained during the time-course of the infestation. Conclusions Resistance mechanism associated to the cassava whitefly-resistant accession ECU72 is an antixenosis strategy based on reinforcement of cell walls. Both resistant and susceptible accessions respond differently to whitefly attack at biochemical level, but the inherent metabolic differences are directly linked to the resistance phenotype rather than an induced response in the plant.

Members of the genus Torradovirus (family Secoviridae, type species Tomato torrado virus, ToTV) are spherical plant viruses transmitted by the whitefly species Trialeurodes vaporariorum and Bemisia tabaci. Knowledge on the mode of vector transmission is lacking for torradoviruses. Here, the mode of transmission was determined for Tomato marchitez virus (ToMarV). A minimal acquisition access period (AAP) and inoculation access period (IAP) of approximately 2h each was required for its transmission by T. vaporariorum, while optimal transmission required an AAP and IAP of at least 16h and 8h, respectively. Whiteflies could retain the virus under non-feeding conditions for at least 8h without loss of transmission efficiency, but upon feeding on a non-host plant in between the AAP and IAP they retained the virus for no more than 8h. Similar conditions supported transmission of isolates of ToTV and Tomato chocolàte virus (ToChV) by T. vaporariorum and B. tabaci. Additionally, similar experiments revealed the banded-winged whitefly (Trialeurodes abutilonea) as a vector for all three virus species. The results are congruent with acquisition and retention periods for semi-persistent virus transmission. RT-PCR detection analysis of ToTV and ToMarV in the vector's body revealed their presence in the stylet, but not in the head where the pharynx of the foregut is located. The results altogether indicate a semi-persistent stylet-borne mode of vector transmission for torradoviruses. Additionally, this is the first group of spherical viruses transmitted by at least three different species of whiteflies.

Solanum galapagense is closely related to the cultivated tomato and can show a very good resistance towards whitefly. A segregating population resulting from a cross between the cultivated tomato and a whitefly resistant S. galapagense was created and used for mapping whitefly resistance and related traits, which made it possible to study the genetic basis of the resistance. Quantitative trait loci (QTL) for adult survival co-localized with type IV trichome characteristics (presence, density, gland longevity and gland size). A major QTL (Wf-1) was found for adult survival and trichome characters on Chromosome 2. This QTL explained 54.1 % of the variation in adult survival and 81.5 % of the occurrence of type IV trichomes. A minor QTL (Wf-2) for adult survival and trichome characters was identified on Chromosome 9. The major QTL was confirmed in F3 populations. Comprehensive metabolomics, based on GCMS profiling, revealed that 16 metabolites segregating in the F2 mapping population were associated with Wf-1 and/or Wf-2. Analysis of the 10 most resistant and susceptible F2 genotypes by LCMS showed that several acyl sugars were present in significantly higher concentration in the whitefly resistant genotypes, suggesting a role for these components in the resistance as well. Our results show that whitefly resistance in S. galapagense seems to inherit relatively simple compared to whitefly resistance from other sources and this offers great prospects for resistance breeding as well as elucidating the underlying molecular mechanism(s) of the resistance.

We studied the capacity of one species of predator to control two major pests of greenhouse crops, Western flower thrips (Frankliniella occidentalis (Pergande)) and the greenhouse whitefly (Trialeurodes vaporariorum (Westwood)). In such a one-predator¿two-prey system, indirect interactions can occur between the two pest species, such as apparent competition and apparent mutualism. Whereas apparent competition is desired because it brings pest levels down, apparent mutualism is not, because it does the opposite. Because apparent competition and apparent mutualism occurs at different time scales, it is important to investigate the effects of a shared natural enemy on biological control on a time scale relevant for crop growth. We evaluated the control efficacy of the predatory mites Amblyseius swirskii (Athias-Henriot) and Euseius ovalis (Evans) in cucumber crops in greenhouse compartments with only thrips, only whiteflies or both herbivorous insects together. Each of the two predators controlled thrips, but A. swirskii reduced thrips densities the most. There was no effect of the presence of whiteflies on thrips densities. Whitefly control by each of the two predators in absence of thrips was not sufficient, yet better with E. ovalis. However, whitefly densities in presence of thrips were reduced dramatically, especially by A. swirskii. The densities of predators were up to 15 times higher in presence of both pests than in the single-pest treatments. Laboratory experiments with A. swirskii suggest that this is due to a higher juvenile survival and developmental rate on a mixed diet. Hence, better control may be achieved not only because of apparent competition, but also through a positive effect of mixed diets on predator population growth. This latter phenomenon deserves more attention in experimental and theoretical work on biological control and apparent competition.

Plant responses induced by zoophytophagous plant bugs (Miridae) have not been thoroughly studied. Here, we show that three different zoophytophagous predators (Nesidiocoris tenuis, Macrolophus pygmaeus and Dicyphus maroccanus) have different capacities for the induction of responses in tomato plants, resulting in varying degrees of attractiveness of the plants to pests and natural enemies. Tomato plants punctured by N. tenuis were less attractive to the whitefly Bemisia tabaci and to the lepidopteran Tuta absoluta. In contrast, tomato plants punctured by M. pygmaeus and D. maroccanus were not able to repel B. tabaci and, more interestingly, became more attractive to T. absoluta. The ability of N. tenuis to make tomato plants less attractive to B. tabaci was attributed to the activation of the abscisic acid (ABA) signaling pathway, which was only up-regulated in plants punctured by N. tenuis. However, the phytohormones involved in the behavioral responses of T. absoluta could not be identified; therefore, further studies are required. Additionally, all three zoophytophagous mirid predators activated jasmonic acid (JA) signaling pathways, which resulted in the parasitoid Encarsia formosa being attracted to tomato plants. Here, the implications of these results on the efficacy of these three predators as biocontrol agents are discussed. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under the Grant agreement n°265865 and by the Spanish Ministry of Science and Innovation (AGL2011-30538-C03) and the Conselleria d’Agricultura, Pesca i Alimentació de la Generalitat Valenciana. The authors thank Javier Calvo (KOPPERT BS) for supplying the insects and Universitat Jaume I-SCIC for providing technical support.

Semi-natural habitats in agricultural landscapes may support parasitoid populations that provide biocontrol services by suppressing populations of crop pests, but little is known about the spatial pattern and variability of these services at different levels of scale. Here we investigate the rarely studied phenomenon of early-season crop colonization by parasitoids and the relationship with the surrounding landscape. We assessed parasitism of whiteflies by placing whitefly infested cotton seedlings in remnant vegetation, arable land 25–125 m from remnant vegetation, and arable land further than 400 m from remnant vegetation. Twelve to twenty sentinel plants were exposed in a 25 × 25 m grid pattern in plots in each habitat. The experiment was conducted at 18 locations across two landscapes and repeated three times in a 2-week period in 2007 and 2008. Parasitism was observed during the first three days after the introduction of the whitefly infested seedlings and was in all cases caused by Encarsia spp. The mean number of parasitized whitefly per plant was 0.106 ± 0.025 and was highest on cotton plants placed in remnant vegetation, declining with increasing distance from remnant vegetation. A regression model with land use and meteorological variables received more statistical support from the data than models with only landscape and time period as factors. Parasitism levels were influenced by the proportion of remnant vegetation, grassland, as well as wind, temperature, dew point temperature and year. Early-season colonization of whitefly infested seedlings by parasitoids was erratic and characterized by large spatial (inter-plant and inter-plot) and temporal variation. Our study confirms that remnant vegetation function as reservoirs for parasitoids and that parasitoids can penetrate arable fields beyond 125 m within 3 days. However, variation in the occurrence of parasitism makes it difficult to predict parasitoid colonization at a specific place and time. Therefore, field-based scouting for pests and parasitoids is necessary, even in landscapes with a high biocontrol potential.

Bead-based suspension array systems enable simultaneous fluorescence-based identification of multiple nucleic acid targets in a single reaction. This study describes the development of a novel approach to plant virus and vector diagnostics, a multiplexed 7-plex array that comprises a hierarchical set of assays for the simultaneous detection of begomoviruses and Bemisia tabaci, from both plant and whitefly samples. The multiplexed array incorporates genus, species and strain-specific assays, offering a unique approach for identifying both known and unknown viruses and B. tabaci species. When tested against a large panel of sequence-characterized begomovirus and whitefly samples, the array was shown to be 100% specific to the homologous target. Additionally, the multiplexed array was highly sensitive, efficiently and concurrently determining both virus and whitefly identity from single viruliferous whitefly samples. The detection limit for one assay within the multiplexed array that specifically detects Tomato yellow leaf curl virus-Israel (TYLCV-IL) was quantified as 200 fg of TYLCV-IL DNA, directly equivalent to that of TYLCVspecific qPCR. Highly reproducible results were obtained over multiple tests. The flexible multiplexed array described in this study has great potential for use in plant quarantine, biosecurity and disease management programs worldwide. (C) 2014 Elsevier B.V. All rights reserved.

The solitary parasitoid Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) is one of the key biological control agents of the whitefly Bemisia argentifolii Bellows & Perring, also known as B. tabaci (Gennadius) B-biotype (Homoptera: Aleyrodidae). We present new information on its biology, and particularly about larval elimination during the first instar in cases of superparasitism. For the first time, physical elimination of supernumerary larvae was observed, both outside and inside the host. These findings are documented with confocal microscopy images and video recordings. We observed more than 350 B. argentifolii nymphs, parasitized with one, two or more than two larvae. Physical attack took place only when parasitoid eggs were laid in contact with each other. In this case the percentage larval mortality outside the host was significantly higher (45.7%) than in cases of single larvae (12.0%) or larvae hatched under the same host but not in contact with each other (23.3%). These new findings are important in view of a possible horizontal transfer of a parthenogenesis inducing Wolbachia bacterium from a thelytokous to an arrhenotokous strain, with the aim of augmenting the biological control of B. argentifolii.

International audience; A new icosahedral DNA virus was isolated from aphids (Myzus persicae) that showed abnormal growth and development. The purified virus particles have a diameter of 20 nm and contain a single-stranded DNA molecule of approximately 5.7 kb. The viral particles are composed of five structural proteins (92, 85, 68, 64, and 57 kDa). As the main biophysical properties of this virus are similar to those of the members of the genus Densovirus it was tentatively named Myzus persicae densovirus (MpDNV). A PCR-based detection method and a polyclonal antiserum raised against MpDNV allowed the detection of the virus in a single-infected aphid. MpDNV is immunologically related to Junonia coenia densovirus, but not to other members of the subfamily Densovirinae. Biological assays showed that MpDNV could be both transmitted transovarially and horizontally via honeydew and saliva. MpDNV was able to infect whiteflies but not other aphid species tested.

International audience; The genomes of two Watermelon chlorotic stunt virus (WmCSV) isolates, one from the Sudan and one from Iran, were cloned and sequenced. Sequence relationship with other geminiviruses characterizes WmCSV as a typical Eastern Hemisphere geminivirus with a bipartite genome. The two geographically distant WmCSV isolates from Africa and the Middle East share a very high overall sequence similarity: 98% between their DNA-A and 96% between their DNA-B components, and their respective capsid proteins are identical. A single amino acid change in the capsid protein (N131D) renders WmCSV whitefly nontransmissible. This region of the capsid is also implicated in transmission by Bemisia tabaci of Tomato yellow leaf curl virus.