Recovering plant-associated arthropod communities by eDNA metabarcoding historical herbarium specimens.

Natural history collections are a priceless resource for understanding patterns and processes of biodiversity change in the Anthropocene. Herbaria, which house millions of historical plant records from all over the globe, are particularly valuable to study population genetics of the plants themselves and to understand the assembly of plant-associated microbial communities. Here we test if herbaria can serve yet another essential purpose, namely to provide information on the historical assembly of plant-arthropod interactions. The specificity and temporal stability of these associations are poorly known. Considering their pivotal role in the assembly of terrestrial food webs, this knowledge is paramount to understanding the consequences of global change. We use environmental DNA (eDNA) metabarcoding to characterize communities of plant-associated arthropods from archived herbarium specimens of different ages and origins. The herbarium specimens yield arthropod DNA across various ecological guilds and trophic levels over multiple decades. In an experiment, we also show that the typical dry storage of plants in herbaria does not alter the recovered arthropod diversity and community composition. By analyzing a time series of leaf samples from a forest monitoring project, we then characterize changes in arthropod biodiversity over two decades, showing that archived plants can also provide the time series data that are urgently needed to understand arthropod declines. This use of herbaria and plant archives promises unprecedented insights into plant-arthropod interactions and revolutionizes our ability to monitor spatiotemporal changes in interaction diversity.