Herbivory of native and exotic North-American prairie grasses by nymph Melanoplus grasshoppers

Abstract

Although the general interaction between native and exotic plants and specialist insect herbivores has received considerable attention in ecological studies, plant responses to herbivory by generalist insects, as well as feeding preferences of generalist insects, are still poorly understood. Experimental studies comparing leaf damage of native and exotic plants to generalist insects have provided inconsistent results due to irregularities in methodology such as using only one type of experiment or using nonstandard measurements. Our study addresses these issues by examining leaf damage caused by generalist Melanoplus grasshoppers in morphologically and physiologically similar native (Andropogon gerardii and Bouteloua curtipendula) and exotic grasses (Miscanthus sinensis and Bothriochloa ischaemum) in Ohio and Maryland. In a 2-year study, we explored whether exotic grasses sustain less damage than native grasses, and consequently, whether generalist grasshoppers may potentially pose biotic resistance to exotic grasses. Using a combination of choice and nochoice feeding experiments with intact plants and with clipped leaves under different (field and greenhouse) conditions, we found that overall both herbivory and grasshopper performance (body length) were greater on the exotic grasses compared to native grasses. Our results suggest that exotic grasses which do not share a coevolutionary history with native generalist Melanoplus grasshoppers might have lower physical and chemical defenses than native plants. Consequently, Melanoplus grasshoppers may provide biotic resistance to these exotic grasses should these plants invade natural areas at the study regions. These results have important applications for predicting the interaction between exotic plants and generalist herbivores in the introduced range, which is critical for understanding factors facilitating plant invasions.

Responses of grassland arthropods to an invasion by nonnative grasses

“…Generalist herbivores may be more likely to feed on novel plant species than forage-specialized arthropods (Strong et al 1984;Tallamy 2004). Consequently, taxa dominated by polyphagous species might be less vulnerable to invasions that displace their native food sources, especially if nonnative grasses lack effective defenses against evolutionarily novel herbivores (Parker et al 2006;Avanesyan and Culley 2015). They might even increase in abundance if nonnative plants produce more biomass than native species.…”

Defoliation reduces soil biota – and modifies stimulating effects of elevated CO2

“…The average of all units was 14.4 cm ±3.9 with no treatment differences. At each defoliation event, the vegetation was cut down by 1/6 of the pretreatment median height in each individual defoliation unit to simulate the effect of foliar insect herbivores such as grasshoppers (e.g., Avanesyan and Culley ). Thus, by the end of the treatment, the defoliation had removed 2/3 of the original vegetation, and the median height was approximately 8–10 cm above the soil, depending on the original median height.…”

Should I Eat or Should I Go? Acridid Grasshoppers and Their Novel Host Plants: Potential for Biotic Resistance

“…The biotic resistance hypothesis is particularly well explored in studies on invasive plants [20], and it predicts that native generalist herbivores will prefer to feed on introduced plants that do not share coevolutionary history with these native herbivores, and, therefore, will be less defended compared to native plants [18]. Following Maron and Vilà [18], many studies published in subsequent years demonstrated that exotic plants can be preferentially consumed in a plant’s introduced range by non-coevolved native herbivores [11,19,21,22,23,24,25,26,27,28]. Similar results on generalist herbivores’ preferences for exotic plants were also obtained from studies on non-insect invertebrates [29].…”

“…Many authors emphasized that by incorporating exotic plants into their diet, native generalist insect herbivores can contribute to the biotic resistance of native communities to plant invasions [19,22,25,27,28]. In this regard, orthopterans, which are the most abundant aboveground insects [30], and particularly grasshoppers, are especially unique study organisms for exploring the role of native generalist insect herbivores in the biotic resistance of native communities.…”

“…Thus, researchers can investigate the feeding responses from grasshoppers to a wide range of introduced plants—plants with different life forms, perenniality, etc., and presumably different herbivore resistance and tolerance traits. Finally, previous studies have shown that grasshoppers can utilize introduced plants [13,25,26,27,28,32], including highly invasive plants [33]. So, researchers can explore grasshopper feeding patterns on the introduced plants and grasshoppers’ potential for suppressing plant growth and preventing plant establishment in the introduced range.…”