Variation in the guild composition of herbivorous insect assemblages amongco-occurring plant species

Variation in plant traits among plant species may promote the development o f a characteristic functional assemblage of insect herbivores associated wi th each plant species. However, only a small number of studies have detaile d the representation of several herbivore guilds among co-occurring plant s pecies to determine whether the functional structure of herbivorous insect assemblages varies widely and consistently among plant species. The present study provides one of the few published data sets reporting on the density of several guilds of insect herbivores among numerous plant species. Varia tion in guild associations with plant phenology and season are also describ ed. Insect herbivores were divided into 10 guilds, and the representation o f these guilds was examined for 18 co-occurring plant species. Guild densit ies and assemblage composition varied significantly among plant species, ev en when variation over time was taken into account. Variation in guild dens ities and assemblage composition were not strongly related to the taxonomic relationships of the plants. The highest densities of several guilds occur red in spring and summer, although other guilds were not strongly seasonal. Certain guilds were strongly associated with the presence of new leaves, w hereas other guilds appeared to prefer mature leaves. This resulted in asse mblage differences between samples containing new and mature leaves and sam ples containing mature leaves only. Even though the timing and duration of leaf and flower production varied among plant species, this did not explain all variation in guild densities among plant species. It is suggested that additional factors, including plant traits, are contributing to the wide a nd consistent variation in herbivore assemblage composition among plant spe cies.