Assessment of pospiviroid transmission by Myzus persicae, Macrolophus pygmaeus and Bombus terrestris

During the past decade, pospiviroid outbreaks in tomato and sweet pepper crops have been regularly reported worldwide. Although seed transmission was often suspected, transmission from asymptomatic ornamentals and weeds through pruning tools, or via insect vectors could not be excluded. To evaluate the risk of pospiviroid transmission via insects, three insect spp. commonly observed in these crops were used in multiple transmission experiments with Potato spindle tuber viroid (PSTVd), Tomato apical stunt viroid (TASVd), Pepper chat fruit viroid (PCFVd) and Tomato chlorotic dwarf viroid (TCDVd)-infected source plants, such as tomatoes, petunias and peppers. The insect species belong to three different functional groups: a phloem-feeding pest (Myzus persicae Sulzer), a pollinator (Bombus terrestris L.) that feeds on pollen and nectar, and a generalist predator (Macrolophus pygmaeus Rambur), that consumes several species of insect pests and feeds on plant saps and pollen. For each insect, four transmission experiments were conducted in which different receptor host plants were challenged. During the experiments, insects that were seen probing or feeding on were captured and tested for viroids using PCR. The percentage of each insect species that was pospiviroid positive was 100 % for M. persicae, 4 % B. terrestris, and 0 % for M. pygmaeus. Although these results indicate that M. persicae may be a vector, none of the receiving host plants in four separate experiments tested positive. However, transmission by B. terrestris is possible since one of 18 receiving tomato plants tested positive for TCDVd in one of four transmission experiments, resulting in an overall transmission rate of 2.6 %. Based on these results, we believe that the use of pollinating insects and biological control agents in greenhouses does not imply a major phytosanitary risk for viroid dispersal.