Interaction of native and invasive grasses with a generalist herbivore insect
Invasive species and their ability to outcompete native species can cause significant environmental problems on different levels: from economic losses and human health problems to changes in natural communities and the loss of biodiversity. The overall goal of this study is to provide greater insight into the successful invasion of introduced plant species, by determining whether an interaction with native generalist herbivores, such as grasshoppers, is a major factor enabling invasive plants to succeed in the introduced range. We address this question from two perspectives simultaneously: (1) resistant responses of invasive versus native plant species (leaf damage) to feeding by grasshoppers; and (2) the feeding preferences of grasshoppers (feeding behavior) with regard to these same plant species. Feeding experiments using invasive (Miscanthus sinensis, ‘Zebrinus’ and ‘Gracillimus’ cultivars) and native (Andropogon gerardii and Bouteloua curtipendula) grasses, as well as their leaves, and nymph grasshoppers of the Melanoplusgenus were conducted under field and lab conditions. Leaf damage (the volume of the grazed portion and frequency of “scarring”) and feeding behavior of grasshoppers (food intake, food assimilation, and feeding activity) were estimated and compared between native and invasive plant species.
In field experiments with intact plants, the volume of grazed portion, number of scars, and frequency of “scarring” were greater in invasive (M. sinensis ‘Zebrinus,’ M. sinensis ‘Gracillimus’) plants than in native (A. gerardii, B. curtipendula) plants (P<0.05). Also, the feeding activity of grasshopper nymphs was higher on invasive plants (P<0.05). However in the experiments with leaves, we did not observe any feeding preferences of grasshoppers or any differences in their food intake and food assimilation on native or invasive plants species (P>0.05). These results suggest that the feeding behavior of grasshoppers differs under natural and artificial conditions, and that these plant species may change their resistance level after they have been clipped.