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 we stern corn rootworm, Diabrotica virgifera virgifera, with significantly mor e sweet corn and winter squash pollen consumed than that of common sunflowe r and Canada goldenrod. Sequential solvent extraction and chromatographic f ractionation of host pollens, guided by a feeding bioassay of respective fr actions, isolated dominant phagostimulatory activity in pools of free amino acids. Amino acid profiles were determined by TLC and HPLC analysis. For s weet corn pollen, proline was predominant, accounting for 70% of a total 95 .3 mu mol free amino acid/g pollen; serine, alanine, gamma-aminobutyric aci d (GABA), and asparagine occurred in decreasing order of concentration. In squash pollen, beta-alanine predominated (30% of 111 mu mol amino acid/g po llen), followed by asparagine, alanine, proline, and GABA. Histidine (42% o f 83.8 mu mol amino acid/g pollen), proline, aspartic acid, asparagine. and alanine were dominant for sunflower pollen; and for goldenrod, proline (51 % of 50.6 mu mol amino acid/g pollen), trans-hydroxyproline, serine, histid ine, and alanine predominated. The five dominant amino acids from each poll en accounted for 80-90% of total amino acid content. Simple mixtures of som e dominant amino acids, approximating levels found in sweet corn and squash pollen, gave phagostimulation similar to that of the crude extracts.