The Wheat dwarf virus, the causal agent of the wheat dwarf disease, is transmitted by leafhoppers from the genus Psammotettix and currently the main protection strategy is based on the use of insecticide treatments. Sustainable management strategies for insect vectors should include methods that are targeted to disrupt reproductive behavior and here we investigated the mating behavior of Psammotettix alineus (Dahlbom 1850) in order to determine the role of vibrational signals in intra-specific communication and pair formation. Both genders spontaneously emit species- and sex-specific calling songs that consisted of regularly repeated pulse trains and differ primarily in pulse train duration and pulse repetition time. Females preferred the conspecific male calling song. After a coordinated exchange of pulse trains, the male approached the stationary female. During the close range courtship and also immediately prior to copulatory attempts distinct male vibrational signals associated with wing flapping and wing vibrations were recorded from the substrate. In the presence of a receptive female, competing males emitted vibrational signals most likely aimed to interfere with male-female interaction. Mated females regained sexual receptivity after they laid eggs. Although results suggest that the viruliferous status of insects may have an effect on vibrational songs, our current results did not reveal a significant effect of virus on leafhopper performance in mating behavior. However, this study also suggests, that detailed understanding of plant-vector-virus interactions relevant for vector mating behavior is essential for trying new approaches in developing future control practices against plant viruses transmitted by insect vectors.

Wheat dwarf virus, transmitted by the leafhopper Psammotettix alienus in a persistent, non-propagative manner, infects numerous species from the Poaceae family. Data associated with wheat dwarf virus (WDV) suggest that some isolates preferentially infect wheat while other preferentially infect barley. This allowed to define the wheat strain and the barley strain. There are contradictory results in the literature regarding the ability of each of these two strains to infect its non-preferred host. To improve knowledge on the interactions between WDV strains and barley and wheat, transmission experiments were carried out using barcoded P. alienus and an experimental design based on single/sequential acquisitions of WDV strains and on transmissions to wheat and barley. Results showed that (I) WDV strains are transmitted with similar efficiencies by P. alienus males, females and larvae, (II) WDV wheat and barley strains do not infect barley and wheat plants, respectively, and (III) a functional transcomplementation between the wheat and barley strains allows a mixed infection of barley and wheat. The described ability of each WDV strain to infect a non-host plant in the presence of the other viral strain must be considered to analyze data available on WDV host range.Viruses 2020, 12, 34 2 of 15The WDV genome also contains two non-coding sequences (the long and short intergenic regions (LIR and SIR, respectively)) which contain sequences important for viral replication and for the regulation of gene expression [7]. Phylogenetic studies carried out with complete WDV genomic sequences obtained from isolates sampled on different host species evidenced two main groups, including, respectively, the originally described wheat (noted WDV-W in this study) and barley (WDV-B in this study) strains [8,9]. The WDV genetic diversity has been further categorized into clades (A to E) based on sequence similarity and phylogenetic relationships [10]: the WDV-W group includes clades C, D and E, whereas WDV-B includes clades A (subdivided into A1 and A2 [11]) and B. WDV-B and WDV-W strains show 83-84% nucleotide identity [12], LIR and SIR being the most variable genomic regions [13]. Nucleotide identity is above 94% between WDV-B isolates and above 98% between WDV-W isolates [13][14][15][16][17].WDV is transmitted from plant to plant in a persistent, non-propagative manner [18] by leafhoppers from the genus Psammotettix (Hemiptera, Cicadellidae, Deltocephalinae), a Holartic species commonly found in cereal fields and in grassland [19,20]. Morphological characteristics of these insects can be used to assign leafhoppers to the genus Psammotettix [21,22]. However, the accurate identification of Psammotettix species requires a morphological description of the male genitalia (i.e., aedeagus), which does not allow the assignment of females to the Psammotettix species. Due to the complex taxonomy of the Psammotettix spp., criteria used to identify leafhoppers species are poorly described in WDV studies. This could lead to some conflicting resul...