Isolation and identification of primary metabolite feeding stimulants for adult western corn rootworm, Diabrotica virgifera virgifera leconte, from host pollens

Consumption of pollens from several host plants was quantified for adult western corn rootworm, Diabrotica virgifera virgifera, with significantly more sweet corn and winter squash pollen consumed than that of common sunflower and Canada goldenrod. Sequential solvent extraction and chromatographic fractionation of host pollens, guided by a feeding bioassay of respective fractions, isolated dominant phagostimulatory activity in pools of free amino acids. Amino acid profiles were determined by TLC and HPLC analysis. For sweet corn pollen, proline was predominant, accounting for 70% of a total 95.3 μmol free amino acid/g pollen; serine, alanine, γ- aminobutyric acid (GABA), and asparagine occurred in decreasing order of concentration. In squash pollen, β-alanine predominated (30% of 111 μmol amino acid/g pollen), followed by asparagine, alanine, proline, and GABA. Histidine (42% of 83.8 μmol amino acid/g pollen), proline, aspartic acid, asparagine, and alanine were dominant for sunflower pollen; and for goldenrod, proline (51% of 50.6 μmol amino acid/g pollen), trans- hydroxyproline, serine, histidine, and alanine predominated. The five dominant amino acids from each pollen accounted for 80-90% of total amino acid content. Simple mixtures of some dominant amino acids, approximating levels found in sweet corn and squash pollen, gave phagostimulation similar to that of the crude extracts.