The biology and the biomass impact of Blastobasis repartella (Dietz) (Lepidoptera: Coleophoridae) on switchgrass

ABSTRACT The biology and the biomass impact of Blastobasis repartella (Dietz) (Lepidoptera: Coleophoridae) on switchgrass Veronica Calles Torrez, Insect Biodiversity Laboratory, Department of Plant Science, South Dakota State University – Brookings, SD; Dr. Paul J. Johnson, Insect Biodiversity Laboratory, Department of Plant Science, South Dakota State University – Brookings, SD; Dr. Arvid Boe, Department of Plant Science, South Dakota State University – Brookings, SD The switchgrass moth (Blastobasis repartella (Dietz)) is a recently recognized host specific borer in switchgrass (Panicum virgatum L.). Switchgrass is a native North American species under study as a potential biomass production crop and it is important as a model organism for native species-based biofuel synthesis. The late-instar larva feeds in the basal internodes of the tillers, causing premature death of tillers that directly affect biomass accumulation. The focus of this report was to provide new information on the biology of the insect, data on the frequency of tiller infestation among switchgrass cultivars, and differences in above-ground biomass production and biomass loss. Sampling of tillers in 2011 was conducted in an 8-yr-old stand and a 4-yr-old stand at Aurora, South Dakota. Both plots were arranged in a RCB design with six replications of six cultivars. A 0.30 m2 frame was used to delimit sample areas and all tillers within were cut at ground level. Tillers were categorized as infested and uninfested, counted, dried at room temperature, and weighed. Analysis by ANOVA for differences was used and LSD to compare means. The early instar larva feeds on the new tiller bud formed on subterranean rhizomes from late summer through winter, the frequency of infestation was the same among cultivars in each stand, and differences among cultivars were seen in biomass yield and in biomass loss in the 4-yr-old plants due to tiller infestation but not in the 8-yr-old plants. The larva directly affected biomass accumulation in younger plants during early seasonal growth stages, and this is subsequent to damage on rhizome and tiller buds below ground during the winter. Differences between plant age classes may be due to changes in plant vigor and tiller production rates, and increasing larval parasitism rates.