Few insects have been identified as potential pests of switchgrass, and early studies indicate the species is not a preferred host for many insect species (Davis 1914; Walkden 1943). Switchgrass typically is an inferior host relative to other warm-season crops (Nabity et al. 2011; Prasifka et al. 2011a), and fall armyworm (Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)) has reduced survivorship on switchgrass compared with other grasses (Nabity et al. 2011). Variation in armyworm resistance among switchgrass strains cultivars also has been observed (Dowd and Johnson 2009).

While insect damage has been considered minimal, there is potential for this to increase if or when switchgrass for bioenergy systems scale up (Parrish and Fike 2005). Little published data is available on insect pressures during establishment. However, corn flea beetle Chaetocnema pulicaria (Chrysomelidae) damage has been common in Virginia plantings (Dale Wolf, personal communication) and insect pressures during the seedling stage likely represent greatest insect threat to the switchgrass stand productivity.

Grasshoppers (Saltatoria) are known to feed on switchgrass, but the extent of the damage has not been quantified (Parrish and Fike 2005). Schaeffer et al. (2011), in a baseline study of insects in Nebraska switchgrass stands, found that about 60% of arthropods collected were of the orders Thysanoptera and Hymenoptera; leafhoppers, grasshoppers, grass flies and wire worms were noted as the most abundant of potential pest species.

Life stages, geographic distribution, and the symptoms of a stem­boring caterpillar, Blastobasis repartella (Dietz.), recently have been described (Adamski et al. 2010; Prasifka et al. 2010). Switchgrass is the only known host for this caterpillar (Prasifka et al. 2011b), and in a distributional survey B. repartella was found both in cultivated and natural switchgrass stands in eight northern USA states (Prasifka et al. 2010). The species was not observed at southern locations (Arkansas, Louisiana, Oklahoma, and Texas) but lack of observation could not rule out presence at these latitudes. In four northern states (Illinois, Nebraska, South Dakota, and Wisconsin) 1 to 7% of tillers were damaged by B. repartella.

A new species of gall midge (Chilophaga virgate Gagne (Diptera: Cecidomyiidae)) was recently discovered in South Dakota, USA (Boe and Gagne 2011). Proportion of tillers infested with the gall midge in 10 switchgrass genotypes ranged from 7 to 22%. The mass of infested tillers was 35% lower than that of normal tillers, and infested tillers produced no appreciable seed. Such insect pests and associated yield reductions may well become more evident or more common as switchgrass is grown more extensively.