Comparative study of the insect community visiting flowers of invasive goldenrods (Solidago canadensis and S. gigantea)

Abstract

Giant and Canadian goldenrods (Solidago gigantea and S. canadensis, respectively) are two closely related insect-pollinated plants of the family Asteraceae, native to North America and invasive in the Palearctic region. Here we study the structure of the flower-visitor community associated with these species in seven sites from three geographic locations in Central Russia throughout two flowering seasons, using qualitative (visitor set) and quantitative (visitation rate and relative frequency of different functional groups of flower-visiting insects) approaches. These species do not have a specific visitor set and are visited by a wide range of insects. Most differences in pollinator sets are in rare occasional visitors rather than specific ones preferring one of the two plant species. Hoverflies, honey bees, muscoid flies, and wasps are the most frequent visitors of goldenrods, though this generalization can be done only after obtaining large samples: brief observations at one site can bring about misleading results due to high spatial and temporal variation. Though intra-species spatial and temporal variation exceeds inter-species variation, all else equal, insect visitation rate to S. gigantea is higher. This is especially true of pronounced anthophilous insects. These results, together with the shown flower constancy of flower visitors, suggest that insects can distinguish between these two species.