The influence of early-season colonizers on later season insect communities of Solidago altissima

While the insect communities of goldenrod (Solidago altissima) have been studied for decades, little attention has been given to the effects of early season herbivorous insects on the structure of later season communities. Feeding damage, and associated upregulation of plant defense metabolites, can influence plant growth and performance as well as the insect community that subsequently colonizes plants. Some insect community members of S. altissima have been studied extensively, but few researchers have focused on how early-season herbivore communities influence colonization by other herbivore species, including gall insects, phloem feeders, and leaf feeders later in the season. In early spring around State College, PA, we marked young stems of plants infested with different herbivores and tracked their growth, development, and herbivore community. We selected four types of stems with natural infestations of: 1) high herbivore load ( >20 individual insects per stem); 2) low herbivore load ( >5 individual insects) and little evidence of feeding damage; 3) stems with evidence of feeding by caterpillars on their terminal bud, and 4) undamaged stems. From May through Oct, we visited stems every two weeks, counted insect occupants, quantified their populations, measured the amount of damage, and measured plant height. At the end of the season, we harvested flowers to get a measure of reproductive output. Our results provide insight on the influence of early-season herbivory on structure of later season insect communities and may help explain occurrence and abundance of key community members.