Network Centrality as an Indicator for Pollinator Parasite Transmission via Flowers

SIMPLE SUMMARY: Understanding the transmission of disease is a key aspect to unravel the epidemiology of a disease. Multiple bee species face a global decline caused by an interplay of several factors, one of which is disease-causing parasites. Laboratory studies have identified that most of these parasites have an oral–fecal transmission route and that flowers may serve as a transmission spot between bee species. Within this study, we look if the transmission of parasites via flowers is actually occurring in the field under natural conditions. Furthermore, we look at plant–pollinator interactions, which can be represented as a network, and show that the centrality of a flower in the plant–pollinator network, weighted by visitation frequency, is a good predictor of the presence of parasites on the flower. In other words, we provide evidence to support the transmission mechanism via flowers in the field and show that flowers that are more central in the plant–pollinator network are most likely to contain parasites. Furthermore, we also explore the mechanism of external vectoring, where parasites hitchhike on the exterior of bees and are deposited on the flowers. This study further paves the path to epidemiological studies using the plant–pollinator network as a tool to assess the transmission of bee parasites. ABSTRACT: Parasites are important actors within ecosystems. However, a key aspect to unraveling parasite epidemiology is understanding transmission. The bee pollinator community harbors several multihost parasites, which have been shown to be able to spread between species via flowers. Hence the plant–pollinator network can provide valuable information on the transmission of these parasites between species. Although several controlled experiments have shown that flowers function as a transmission hub for parasites, the link with the plant–pollinator network has rarely been addressed in the field. Here, one can hypothesize that the most central flowers in the network are more likely to enable parasite transmission between species. In this study, we test this hypothesis in three local plant–pollinator networks and show that the centrality of a plant in a weighted plant–pollinator network is a good predictor of the presence of multihost pollinator parasites on the plant’s flowers.