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Location: Corn Insects and Crop Genetics Research

Title: Stem-boring caterpillars of switchgrass in the midwestern United States

item Prasifka, Jarrad
item Buhay, Jennifer
item Sappington, Thomas
item Heaton, Emily
item Bradshaw, Jeffrey
item Gray, Michael

Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2011
Publication Date: 5/1/2011
Citation: Prasifka, J.R., Buhay, J.E., Sappington, T.W., Heaton, E.A., Bradshaw, J.D., Gray, M.E. 2011. Stem-boring caterpillars of switchgrass in the midwestern United States. Annals of the Entomological Society of America. 104(3):507-514.

Interpretive Summary: Switchgrass is a native perennial prairie grass that is being developed for large scale planting as a biofuel feedstock. Very little is known about the insect species that feed on this plant and how damaging they may become once switchgrass is grown in large acreages. Stands of switchgrass of different ages (1-5 years) were sampled in Illinois and Iowa to characterize the caterpillar species that bore into the stems, as well as details about the damage they cause. Three species were found, one of which was restricted to Illinois. Two of the species, Blastobasis and Haimbachia, may feed only on switchgrass. The third, stalk borer (Papaipema), is better known because it feeds on many plant species and is an occasional pest of corn. It is a relatively large insect that cannot complete development on switchgrass alone because of its small stem size, and there is evidence that the older, larger caterpillars moved out of switchgrass and began feeding on nearby weeds. In some conditions, nearby corn or Miscanthus crops could be at risk of damage by stalk borers leaving switchgrass. Sampling of adult Blastobasis through the night indicated that peak flight activity occurs around 2:30 am. This information will be useful to university, government, and industry scientists and farmers as switchgrass increases in importance as a biofuel crop and is monitored for pest damage.

Technical Abstract: Lepidopteran stem-borers were collected from switchgrass, Panicum virgatum L., tillers showing symptoms of infestation at seven locations in Illinois and Iowa, with additional observations made on larval and adult activity. Blastobasis repartella (Dietz)(Coleophoridae), whose only known host is switchgrass, was common in stands grown for more than five years, while the polyphagous stalk borer, Papaipema nebris (Guenée)(Noctuidae), was abundant in newly established (i.e., first- and second-year) switchgrass. Haimbachia albescens Capps (Crambidae) also was collected from two locations in Illinois, making switchgrass the first known host for this species. Entry holes made by B. repartella and H. albescens were usually 1–2 cm above the soil surface, precluding discrimination between these species based on external appearance of damage. Though P. nebris often entered stems within 5 cm of the soil surface, they also appeared to move between stems and were the only species entering stems at heights above 15 cm. B. repartella adults were active on and above the switchgrass canopy by 2130 hours, with peak activity around 0230. Activity of B. repartella adults appeared greatly reduced on one night with relatively cool temperatures and low wind speeds. Data from switchgrass and giant ragweed, Ambrosia trifida L., suggest P. nebris move out of switchgrass stems during July in search of larger diameter hosts. If weed hosts like giant ragweed are controlled, the risks from movement of P. nebris larvae out of switchgrass and into other crops may be low, as hosts like corn, Zea mays L., or Miscanthus spp. may have outgrown the potential for serious damage.