Sedum as host plants for caterpillars? Introducing gut content metabarcoding to green roof research

Insect populations are declining due to a multitude of causes. One major cause is the loss of suitable habitat. Recently, green roofs have been investigated for their potential to mitigate this loss of habitat in urbanized environments. In Belgium, most installed green roofs are characterized by a thin layer of mineral substrate and a vegetational composition that is mainly dominated by species of Sedum, i.e. extensive Sedum-moss roofs or Sedum-moss-herbaceous planting. Lepidoptera, as well as many other insects, exert specific plant-herbivore interactions during at least one phase in their life cycle, but no attention has been paid to investigate the potential of Sedum to serve as host plants. Using a molecular approach, we identified caterpillar communities on both types of extensive green roofs and investigated their gut contents. Ten nocturnal moth species were identified: eight polyphagous macromoths and two monophagous micromoths. All species were found to feed on Sedum, a first record thereof for every species. Based on these findings we conclude that both types of green roofs provide larval habitat for at least some moth species. This can have broad implications considering the fact that moths play a crucial role in multiple trophic interactions. However, when the goal is to increase butterfly diversity in urban environments, other types of green roofs need to be reconsidered. While we did not observe larvae of diurnal butterfly species, there have been reports of imagines on wildflower green roofs or biodiverse (semi-)intensive green roofs.