Host plant richness and abundance drive populations of a super‐generalist xylem‐feeding insect

Abstract Due to their wide diet breadth, generalist herbivores are often less sensitive to bottom‐up forces compared to specialists. Despite this, some generalist insects can be significantly affected by the diversity and structure of the plant communities. Here, we investigated the effect of habitat and plant richness on the abundance of the super‐generalist meadow spittlebug, Philaenus spumarius (Hemiptera: Aphrophoridae), at both juvenile and adult stages. We sampled 93 sites representing four habitat types (olive groves, vineyards, meadows and field margins) across eight heterogeneous agricultural landscapes in central Italy. Nymphs were sampled by quadrat sampling in April along with the herbaceous vegetation community, while adults were sampled using a sweep net in June, August and October. Nymph abundance was positively associated with plant species richness and vegetation cover at a small scale (2 m 2 ), a scale consistent with the limited movement capability of nymphs, while it did not differ between habitat types. A positive correlation between adult and juvenile densities was also observed. However, this effect weakened towards the end of the growing season. The findings indicate that bottom‐up effects associated with plant community composition can significantly influence the local abundance of a super‐generalist xylem‐feeding insect. The positive relationship between plant species richness and nymph abundance suggests that broad host use does not necessarily buffer P. spumarius against local vegetation effects. Furthermore, the marked weakening of the juvenile–adult abundance relationship is consistent with increased dispersal of adults in the fall. Given that P. spumarius exhibits variability in host use and population dynamics across its distribution range, the strength of these bottom‐up effects, as well as its dispersal patterns, is likely context dependent and may vary across environmental and geographical gradients.