Intraspecific plant chemodiversity at plot level has contrasting effects on arthropod functional groups

Abstract Plant chemistry mediates interactions between plants and their environment. While intraspecific chemodiversity at the individual plant level is well studied, the effects of chemodiversity at the plant community level on arthropod interactions need more attention. We conducted a field experiment to test how intraspecific chemodiversity affects plant–arthropod interactions. We manipulated plots of Tanacetum vulgare L., varying in chemotype richness and composition, and monitored four arthropod functional groups (herbivores, flower visitors, predators, and ants) over three seasons. We hypothesized that higher plot‐level chemotype richness would enhance occurrence across all studied arthropod groups, but have functional group‐specific effects on abundance , resulting in reduced herbivore and ant abundance and increased flower visitor and predator abundance with increased chemotype richness. Using mixed models, we found that increasing plot‐level chemotype richness had a limited effect on most arthropod group occurrences but led to significant changes in abundance. Increasing chemotype richness decreased herbivore abundance, while it increased flower visitor abundance. Predatory arthropods and ants remained largely unaffected. Furthermore, we found that the presence of specific plant chemotypes within a plot had variable effects for herbivores across years, as some chemotypes initially promoted higher abundances but were associated with lower abundances in the later years. We also found that the presence of specific chemotypes had a positive effect on the abundances of various flower visitor taxa. Predators and ants, on the other hand, showed weaker and more variable responses to specific chemotypes. Specifically, higher chemotype richness reduced the abundance of herbivores such as Uroleucon tanaceti (2022 and 2023) and Brachycaudus cardui (2023), while increasing visitation by flower visitors. These results highlight the role of plant chemodiversity in shaping insect communities and influencing ecosystem dynamics. Read the free Plain Language Summary for this article on the Journal blog.