Structure-phagostimulatory relationships for amino acids in adult western corn rootworm, Diabrotica virgifera virgifera

Abstract

The effects of 52 amino acids and derivatives on feeding responses of adult western corn rootworm Diabrotica virgifera virgifera (WCR) were investigated. L-Alanine was the most phagostimulatory amino acid, followed by L-serine, and β-alanine. All three amino acids showed a dose–response pattern but at the highest dose (500 nmol/disk) feeding by WCR decreased. In structure–activity relationship studies, four structural features for stimulating WCR feeding were found. First, terminal carboxyl and amino acid groups must be intact since all structural modifications in these groups led to a considerable decrease in feeding. Second, a hydrophobic region sterically limited to a two-saturated-carbon insert between the amino and carboxyl groups is associated with stimulatory effects at the L-alanine taste receptor. Third, L-alanine and L-serine are much more potent stimulants than the D enantiomers of these amino acids. Fourth, the hydrogen domain on the α-carbon of L-alanine is sterically constrained. A β-hydroxyl group on the amino acid side chain, such as in L-serine, does not reduce stimulatory taste, which indicates the presence of another binding domain. Therefore, L-alanine and L-serine either have separate binding sites on the taste cells of WCR or an un-ionized, polar grouping extending from the hydrophobic domain of the L-alanine binding site is permitted. The three most phagostimulatory amino acids (L-alanine, L-serine, and β-alanine) are nonessential amino acids, suggesting that amino acid sensitivity in WCR may be tuned to quantitatively relevant signals rather than just nutritionally important amino acids in a food.