Effect of resistant and susceptible alfalfa varieties on free amino acids in Acyrthosiphon pisum

Unable to synthesize all amino acids during growth and development, insects must obtain these via food or alternative sources. Plant phloem amino acids are considered a key limiting factor for aphid production performance. To clarify the effects of resistant aphid alfalfa varieties on the free amino acid content of the pea aphid (Acyrthosiphon pisum), the free amino acid content of pea aphids fed on resistant and susceptible alfalfa varieties (resistant variety ‘Gannong 5’ and susceptible variety ‘Hunter River’) and the free amino acid content of the tested plant materials were determined by liquid chromatography-mass spectrometry. The results showed that the tryptophan content of ‘Gannong 5’ was significantly higher than that of ‘Hunter River’ (P < 0.05), with a difference multiple of 2.25. The content of aspartic acid in pea aphids after feeding on ‘Gannong 5’ was significantly higher than in pea aphids fed on ‘Hunter River’ (P < 0.05), with a difference multiple of 1.48. The contents of proline, glycine, histidine, and total amino acids in the pea aphids fed on ‘Gannong 5’ were significantly lower than those in pea aphids fed on ‘Hunter River’ (P < 0.05), with a difference multiple of 0.31, 0.81, 0.61 and 0.86, respectively. The resistant aphid alfalfa variety ‘Gannong 5’ was found to induce changes in the free amino acid content of the pea aphids, which can affect the survival and development of pea aphids by influencing their proline and total amino acid contents. These results provide a theoretical basis for the prevention and control of pea aphids and the screening of high-quality aphid-resistant alfalfa germplasm resources.