The Relationship Between Native Insects and an Invasive Grass (Oplismenus undulatifolius) in the Mid-Atlantic United States

Abstract

Understanding relationships between insects and invasive plant species in their introduced range is important for management of a new invader and prioritization of its control. This study investigates the insect communities associated with Oplismenus undulatifolius (Wavyleaf Basketgrass), an invasive grass in the mid-Atlantic US, and looks at the effect of herbivory on the species’ growth and reproduction. We surveyed aerial and ground-dwelling insect communities in areas with and without Wavyleaf Basketgrass and examined leaf samples from caged and uncaged patches of Wavyleaf Basketgrass for type and amount of insect damage. Insect richness, evenness, and diversity were similar between invaded and uninvaded areas. At the plot level, there was no difference in abundance of insects caught in pitfall traps, but there were more insects captured in sticky traps at the uninvaded area. Orthoptera in general and Rhaphidophoridae specifically, were indicators of uninvaded plots, along with Sciaridae in the Diptera and Scarabaeidae in the Coleoptera. Indicators of the invaded plots included Blattidae within the Blattodea and Staphylinidae and Carabidae within the Coleoptera. Leaf damage was minor; the 6 most heavily damaged leaves lost between 15% and 21% of their leaf area. Punctures, stippling, and mining were the most common types of leaf damage observed, and most leaves had fewer than 25 incidences of damage per leaf. There was no significant difference in leaf damage, plant biomass, or inflorescence production between caged and uncaged plots. Differences in insect community composition in invaded and uninvaded areas may be due to Wavyleaf Basketgrass itself or concomitant increases in plant cover and changes in microclimate. At least some insect groups are using Wavyleaf Basketgrass as habitat, which may be important in areas where excessive deer browse has removed most of the herbaceous layer.