Biology and Rearing of an Emerging Sugar Beet Pest: The Planthopper Pentastiridius leporinus

SIMPLE SUMMARY: Syndrome des Basses Richesses (SBR) is a bacterial yellowing disease of sugar beet (Beta vulgaris) that reduces the sugar content of the root tissue significantly. There is currently neither a cure for the disease nor effective control measures for the main insect vector, the Cixiid planthopper Pentastiridius leporinus. SBR is therefore spreading in Germany and has caused substantial yield losses in recent years. The development of effective control measures requires a better understanding of P. leporinus biology, including its life cycle and feeding behavior. We therefore established methods for the continuous mass rearing of P. leporinus. In host plant choice experiments, we found that the nymphs are polyphagous when offered sugar beet, winter wheat or maize. Life cycle data indicated that adult planthoppers emerge 170 days after hatching, having passed through five larval instar stages. We developed a state-of-the-art qRT-PCR protocol using TaqMan probes to study the prevalence of two bona fide SBR pathogens: Candidatus Arsenophonus phytopathogenicus (Gammaproteobacteria) and Candidatus Phytoplasma solani (stolbur phytoplasma). These were identified during field studies in newly-infected regions of Rhineland-Palatinate and south Hesse, Germany, where we also observed insect mobility patterns in two consecutive years, including the abundance of adults at four locations and soil-depth monitoring of nymphs. We documented the spread of P. leporinus northward and eastward in Germany, accompanied by an increase in the number of SBR-carrying planthoppers. Interestingly, P. leporinus does not appear to hibernate during winter. Stolbur phytoplasma has a significant impact on SBR pathology in sugar beet. ABSTRACT: The rapid spread of the bacterial yellowing disease Syndrome des Basses Richesses (SBR) has a major impact on sugar beet (Beta vulgaris) cultivation in Germany, resulting in significant yield losses. SBR-causing bacteria are transmitted by insects, mainly the Cixiid planthopper Pentastiridius leporinus. However, little is known about the biology of this emerging vector, including its life cycle, oviposition, developmental stages, diapauses, and feeding behavior. Continuous mass rearing is required for the comprehensive analysis of this insect. Here we describe the development of mass rearing techniques for P. leporinus, allowing us to investigate life cycle and ecological traits, such as host plant choice, in order to design agronomic measures that can interrupt the life cycle of nymphs in the soil. We also conducted field studies in recently-infected regions of Rhineland-Palatinate and south Hesse, Germany, to study insect mobility patterns and abundance at four locations during two consecutive years. The soil-depth monitoring of nymphs revealed the movement of the instars through different soil layers. Finally, we determined the prevalence of SBR-causing bacteria by designing TaqMan probes specific for two bona fide SBR pathogens: Candidatus Arsenophonus phytopathogenicus (Gammaproteobacteria) and Candidatus Phytoplasma solani (stolbur phytoplasma). Our data suggest that P. leporinus is spreading northward and eastward in Germany, additionally, the abundance of SBR-carrying planthoppers is increasing. Interestingly, P. leporinus does not appear to hibernate during winter, and is polyphagous as a nymph. Stolbur phytoplasma has a significant impact on SBR pathology in sugar beet.