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. 2009 Feb;75(3):703-10.
doi: 10.1128/AEM.01778-08. Epub 2008 Dec 5.

Molecular Detection, Penetrance, and Transmission of an Inherited Virus Responsible for Behavioral Manipulation of an Insect Parasitoid

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Molecular Detection, Penetrance, and Transmission of an Inherited Virus Responsible for Behavioral Manipulation of an Insect Parasitoid

Sabine Patot et al. Appl Environ Microbiol. .
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Abstract

For insects, the prevalence of numerous vertically transmitted viruses can be high in their host populations. These viruses often have few, if any, pathological effects on their hosts, and consequently, many of them can remain unnoticed for long periods, despite their potential role in the evolution of the host phenotype. Some females of Leptopilina boulardi, a solitary parasitoid of Drosophila larvae, are infected by an inherited virus (LbFV) that manipulates the behavior of the wasp by increasing its tendency to lay eggs in a host that is already parasitized (superparasitism). This behavioral alteration allows horizontal transmission of the virus within superparasitized Drosophila larvae. Using suppressive subtractive hybridization with infected and uninfected lines, we identified one putative viral sequence. Based on this sequence, we developed a simple PCR test. We tested the correlation between the superparasitism phenotype and PCR amplification of the putative viral marker using several experimental conditions (including horizontal transfers) and several parasitoid genotypes. All of the results revealed that there was a perfect match between the superparasitism phenotype and the amplification profile, which validated use of the molecular marker as a tool to track the presence of the virus and provided the first genomic data for this fascinating virus. The results also show that there was very efficient horizontal and vertical transmission of LbFV, which probably explains its high prevalence in the French populations that we sampled (67 and 70% of infected females). This manipulative virus is likely to play a major role in the ecology and evolution of its parasitoid host.

Figures

FIG. 1.
FIG. 1.
Correlation between the egg-laying behavior and the molecular test of viral infection for the Sref and NSref lines (A) and for S and NS phenotype isofemale lines originating from various populations of L. boulardi (B). The boxes indicate the mean number of parasitoid eggs per parasitized host calculated for each female, and the fraction above each box indicates the number of PCR-positive females/number of females tested. M, Madeira line; P1 and P2, Palma de Mallorca lines; R, Rio de Janeiro line; G1 to G17, Gotheron lines. a, uniplex PCRs; b, multiplex PCRs.
FIG. 2.
FIG. 2.
Multiplex PCR amplification for 10 individuals belonging to the NSref and Sref lines. Data for superparasitism behavior are indicated below the gel and show the number of L. boulardi larvae counted in each of the four dissected hosts. Lane 1, 1-kb DNA ladder (Fermentas, St. Leon-Rot, Germany) used as a molecular weight marker; lanes 2 to 6, NSref line individuals; lanes 7 to 11, Sref line individuals; lanes 12 and 13, positive and negative controls.
FIG. 3.
FIG. 3.
Schematic diagram of the viral sequence and putative open reading frame. The arrow indicates the position and direction of the potential open reading frame. The upper line shows the mRNA sequence, and the lower line indicates the DNA sequence. The dotted line indicates the position of the intron. The positions of the primers are indicated on the DNA sequence, and their designations are indicated below the sequence. The numbers in parentheses are the positions of the primers.

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