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Isolation and characterization of host recognition cues in corn roots for larvae of the western corn rootworm (Coleoptera: Chrysomelidae)

E. J. Bernklau, B. E. Hibbard, L. B. Bjostad
Journal of economic entomology 2013 v.106 no.6 pp. 2354-2363
Diabrotica virgifera virgifera, acetone, amino acids, aqueous solutions, behavior modification, bioassays, corn, dicarboxylic acids, esterification, fatty acids, gas chromatography, germination, hexane, host plants, insect behavior, larvae, liquid chromatography, mass spectrometry, neonates, plant extracts, polar compounds, roots, silica, solid phase extraction, sugars
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.