The reed leafhopper (Pentastiridius leporinus) was originally a specialist, limited exclusively to reed grass as a food source. Within a few years, however, it developed into a dangerous pest that attacks not only reed grass but also sugar beets, potatoes, carrots, and onions. Although the insect itself causes only minor damage to plants, it transmits harmful bacteria that cause plant diseases and lead to massive crop failures—especially in sugar beet and potato production. Two bacterial pathogens are responsible for this: one causes SBR (Syndrome Basses Richesses, or low sugar content syndrome), and the other causes stolbur.
Researchers from the Max Planck Institute for Chemical Ecology in Jena and the Fraunhofer Institute for Molecular Biology and Applied Ecology in Giessen investigated how this insect spread so rapidly and what role its microbial flora might have played in the process. The researchers used state-of-the-art sequencing methods and fluorescence in situ hybridization to identify the microbial community and show where it resides in the insect's body.
"We showed that the reed leafhopper hosts at least seven species of bacteria. The leafhopper appears to be completely dependent on three of these species. These symbionts inhabit specific organs and are passed down through generations alongside the eggs. The bacteria contribute to the leafhopper's nutrition by producing essential amino acids and vitamins. Two other bacteria cause the plant diseases SBR and stolbur. These pathogens are transmitted from leafhoppers to host plants, contributing largely to the harmful effects of leafhoppers. The significance of the two remaining bacteria remains unclear," says lead author Heiko Vogel, summarizing the most important findings. Vogel heads the Host Plant Adaptation and Immunity project group in the Department of Insect Symbiosis .
The two plant-pathogenic bacteria are Candidatus Arsenophonus phytopathogenicus, which causes SBR, and Candidatus Phytoplasma solani, which causes stolbur disease. The research team found five other bacterial species in various organs of the reed leafhopper. The genera Purcelliella, Karelsulcia, and Vidania are mutualists that enable a plant-sap diet. These genera compensate for nutritional deficiencies by providing essential amino acids and B vitamins, or by contributing to the biosynthesis of these substances. The significance of the genera Rickettsia and Wolbachia for the insect host remains speculative. "We were particularly amazed by the complexity of the different microbes, as well as by the fact that Rickettsia bacteria can be found in the cell nuclei of many leafhopper tissues," says Martin Kaltenpoth, head of the Department of Insect Symbiosis at the Max Planck Institute.
How the reed planthopper is able to adapt to the highly diverse defense mechanisms of its host plants is still unknown. However, both the bacteria that cause plant diseases and the symbionts could play a role here.
The results of the study serve as the starting point for developing targeted strategies to manipulate the reed leafhopper's bacterial symbionts. One approach is to inhibit the production of specific salivary proteins in the leafhoppers using RNA interference. Double-stranded RNA (dsRNA) is injected against the target gene to accomplish this. "We are currently developing dsRNA-based sprays in Giessen for the environmentally friendly and targeted control of reed leafhoppers and other pests," says Andreas Vilcinskas from the Fraunhofer Institute for Molecular Biology and Applied Ecology .
Further studies are planned to better understand the role of the reed leafhopper's microbial partners and their interactions. These studies should reveal new approaches to combating this devastating agricultural pest.
