Most phytoviruses use insect vectors to spread and infect the surrounding crop plants. Because atmospheric gas concentrations alter the physiology and metabolism of plants, we hypothesize that the concentration of carbon dioxide (CO 2 ) affects the spread of viruses, due to modifications in the feeding behavior of the vector. Tobacco plants, Nicotiana tabacum L. (Solanaceae), and green peach aphids, Myzus persicae (Sulzer) (Hemiptera: Aphididae), were cultivated under ambient (450 p.p.m., termed aCO 2 ) and elevated (800 p.p.m., eCO 2 ) concentrations of CO 2 . For each atmospheric condition, we first evaluated the ability of the Potato virus Y to spread in a small experimental design, from a central infected tobacco plant to two surrounding circles of healthy plants in presence of aphid vectors for 7 days. The number of aphids recovered on each plant and the infection status of the plants (i.e., healthy vs. infected) were assessed at the end of the experiment. We also evaluated the ability of aphids to transmit the virus under the two experimental atmospheres, by immediately transferring a single insect from an infected plant to a healthy one. The presence of virus in healthy plants was then determined. We found that aphid dispersal, as well as the associated spread of viruses, did not differ between the two atmospheres. On the other hand, we found that aphids grown under eCO 2 were more efficient in transmitting viruses to healthy plants compared to aphids reared under aCO 2 conditions. The results of this experiment indicate that: (1) the ability of an aphid vector to spread a phytovirus is not affected by the level of CO 2 at short time and spatial scales, but (2) the concentration of CO 2 may affect plant defenses or the feeding behavior of herbivorous insects, resulting in more efficient viral transmission from the vector to the host plant.

Sitobion miscanthi, an important viral vector of barley yellow dwarf virus (BYDV), is also symbiotically associated with endosymbionts, but little is known about the interactions between endosymbionts, aphid and BYDV. Therefore, two aphids’ geographic populations, differing in their BYDV transmission efficiency, after characterizing their endosymbionts, were treated with antibiotics to investigate how changes in the composition of their endosymbiont population affected BYDV transmission efficiency. After antibiotic treatment, Rickettsia was eliminated from two geographic populations. BYDV transmission efficiency by STY geographic population dropped significantly, by −44.2% with ampicillin and −25.01% with rifampicin, but HDZ geographic population decreased by only 14.19% with ampicillin and 23.88% with rifampicin. Transcriptomic analysis showed that the number of DEGs related to the immune system, carbohydrate metabolism and lipid metabolism did increase in the STY rifampicin treatment, while replication and repair, glycan biosynthesis and metabolism increased in the STY ampicillin treatment. Proteomic analysis showed that the abundance of symbionin symL, nascent polypeptide−associated complex subunit alpha and proteasome differed significantly between the two geographic populations. We found that the endosymbionts can mediate vector viral transmission. They should therefore be included in investigations into aphid–virus interactions and plant disease epidemiology. Our findings should also help with the development of strategies to prevent virus transmission.

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