Insect diversity and pest status on switchgrass grown for biofuel in South Carolina

Switchgrass (Panicum virgatum L.) has tremendous potential as a biomass and stock crop for cellulosic ethanol production or combustion as a solid fuel. The first goal of this study was to assess diversity of insects in a perennial switchgrass crop in South Carolina. A three-year study was conducted to sample insects using pitfall traps and sweep nets at the Pee Dee Research and Education Center in Florence, SC, from 2007-2009. Collected specimens were identified to family and classified by trophic groups, and predominant species were identified. The diversity and density of weeds in the field during the establishment year (2007) were greater than the following years. Insect diversity at the family level varied significantly across sampling dates only for sweep net samples, with diversity peaks in May of each year. Diversity at the trophic-group level showed significant differences for predators in pitfall traps and for predators and herbivores in sweep net samples across sampling dates. The second goal was to determine the potential impact of insect herbivores on switchgrass yield. Selected plots received applications of 1,3-dichloropropene and chloropicrin soil fumigation before planting and foliar applications of acephate during the season. Dry weight biomass was not significantly affected (P > 0.05) by treatments and visible herbivory was limited to sporadic grasshopper feeding. The most abundant herbivore family collected in pitfall traps was Gryllidae and in sweep net samples Cicadellidae. Chewing, sucking and boring feeding guilds were negatively correlated with the biomass of switchgrass in sweep net samples and sucking insects for pitfall traps. Predominant herbivore species were Draeucolacephala sp. and Melanoplus possibly sanguinipes and an undetermined species of Tettigoniidae. The predominant predator was Solenopsis invicta Buren. Assessing arthropod diversity in switchgrass is a first step in identifying potential pests and beneficial insects in this crop. The results of this study provide important information related to the pest status of insects in switchgrass in South Carolina.