|BERNKLAU, ELISA - Colorado State University
|BJOSTAD, LOUIS - Colorado State University
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2013
Publication Date: 12/12/2013
Publication URL: http://handle.nal.usda.gov/10113/58160
Citation: Bernklau, E.J., Hibbard, B.E., Bjostad, L.B. 2013. Isolation and characterization of host recognition cues in corn roots for larvae of the western corn rootworm (Coleoptera: Chrysomelidae). Journal of Economic Entomology. 106(6): 2354-2363.
Interpretive Summary: The western corn rootworm (WCR) is the most important insect pest of corn in the United States and parts of Europe. By feeding on corn roots, WCR causes economic losses due to decreased nutrient uptake and plant lodging, both resulting in yield loss. Currently, insecticides and transgenic corn containing genes that deliver insecticidal proteins are the only available options for its control under continuous corn production. In the current study, behavioral bioassays were used to isolate compounds from seedling corn roots that direct WCR larvae to the plant (host recognition compounds). When a behaviorally-active extract (one that stimulated the WCR larvae to move towards it) was separated into water and organic fractions, significantly more larvae responded to the recombined partitions than to either partition alone, demonstrating that the active material is a blend comprised of both polar (water soluble) and non-polar (lipid soluble) compounds. A series of chemical proceedures were performed to purify the active components in the extract from inactive components. The active polar fraction contained a blend of small sugars, diacids, amino acids, and inorganic compounds. The non-polar partition was comprised of primarily lipids containing specific subcomponents called fatty acyl groups. Additional management tools for WCR larvae could eventually result from further chemical characterization followed by the manipulation of biosynthetic pathways of these compounds. It may also be possible to use the compunds to attract the larvae to granules with insecticide or capsules with nematodes that kill WCR.
Technical Abstract: Behavioral bioassays were used to isolate compounds from germinating corn roots that elicit a host recognition response (tight-turning behavior) by neonate larvae of the western corn rootworm Diabrotica virgifera virgifera LeConte. When a behaviorally-active extract of germinating corn roots was separated into an aqueous partition and a hexane partition, significantly more larvae (P< 0.05) responded to the recombined partitions than to either partition alone, demonstrating that the active material is a blend comprised of both polar and non-polar compounds. When the aqueous partition was separated with reverse-phase solid phase extraction, most of the behavioral activity was retained in the 100% water fraction (F-1). GC-MS analysis determined that F-1 contained a blend of small sugars, diacids, amino acids and inorganic compounds. The non-polar partition was separated on a silica column and the resulting fractions were tested in combination with F-1 from the aqueous separation. More than 70% of larvae responded to the 100% acetone fraction (fraction B) in combination with F-1, and the response to this treatment was significantly higher than responses to the other non-polar fractions or to F-1 alone. Methyl esterification of fraction B, followed by GC-FAME analysis, confirmed that fraction B was comprised of primarily lipids containing fatty acyl groups.