The influence of early season stimuli on late season communities in Solidago altissima

Plants respond to different types of insect herbivory by modifying their defenses, leading to many physiological changes. Different types of herbivory, including damage from gall insects, lead to induced changes in plant chemical and physical defenses, which can alter the subsequent types and amount of herbivory. Despite demonstrations of plant defense modulation in response to herbivory in experimental settings, little attention has been given to the effects of early season insect activity on the structure of late season communities in natural systems.
Solidago altissima, or tall goldenrod, is an abundant native plant species in the eastern U.S. that is colonized by a well-studied insect community. Furthermore, S. altissima is sensitive to at least two volatile environmental cues that prime its defenses. To understand the influence of early herbivore cues on late season herbivory and plant performance in S. altissima, we visited stems every one to two weeks from May through October, counted present insects including galls, measured damage from herbivores, and measured plant height. At peak inflorescence, we harvested flowers to measure reproductive output. We expected to find differences in late season colonizer populations and plant performance based on the initial type of damage or cue plants experienced early in the season.
Our results provide insight on the influence of early-season stimuli on structure of later season insect communities and may help explain occurrence and abundance of key community members. This work demonstrates under field conditions how early season influences can structure arthropod communities, patterns of herbivory, and plant performance.