Can insect pests be vectors of beneficial endophytes?

Insects able to feed on plant vessels are often known to be vectors of plant pathogens. While much is known about the dynamics and ecology of transmission of pathogens, there is very little, if any, knowledge on the transmission of other microorganisms which are not harmful to the host plant. To shed some light on the role of these insects for the ecology of endophytic microorganisms, we used the sap-feeding leafhopper Scaphoideus titanus (vector of the pathogenic Candidatus Phytoplasma vitis) to transmit microorganisms across grapevine plants. S. titanus nymphs were able to transfer the entire bacterial community from adult (donor) plants to bacteria-free micropropagated (acceptor) grapevines. Sequencing of the bacterial 16S rDNA gene unveiled the composition of bacterial endophytic communities in donor plants, vector insects and acceptor plants, and permitted to track the transmission of bacterial communities between insects and plants. After insect feeding, acceptor plants were colonized by complex endophytic communities dominated by Proteobacteria, highly similar to those present in donor plants. Interestingly, a similar bacterial community, but with a higher ratio of Firmicutes, was carried by the insect. When freshly hatched insects fed directly on acceptor plants without prior contact with the donor, they transferred an entirely different bacterial community dominated by Actinobacteria, where the opportunistic human pathogen Mycobacterium abscessus played a major role. Plant roots were also colonized by complex microbial communities as rich as those found in plant stems, despite little or no direct contact with the insect. We demonstrated for the first time the capability of insect vectors to transfer entire bacterial communities across plants. Feeding on adult plants changed the spectrum of bacteria transmitted by the insect. This drastic change may be explained with the acquisition by the insect of the bacterial communities from the donor plant.