Differential accumulation of leucine and methionine in red and green pea aphids leads to different fecundity in response to nitrogen fertilization

BACKGROUNDNitrogen fertilization affects plants directly and herbivorous insects indirectly. Although insect species and even genotypes are known to differ in their responses to nitrogen fertilization, the physiological and molecular mechanisms remain unclear. This study assessed the fecundity and related regulatory signaling pathways in the green and red morphs of pea aphid (Acyrthosiphon pisum) feeding on Medicago truncatula with and without nitrogen fertilization. RESULTSNitrogen fertilization significantly increased foliar amino acid concentrations and consequently increased the concentrations of several individual essential amino acids in body tissue of the green morph. The increased concentration of Leu, Ile, Met and Val was consistent with enhanced biosynthesis of these amino acids in the endosymbiont Buchnera. Under nitrogen fertilization, Leu and Met accumulated in the green morph enhanced the target of rapamycin (TOR) signaling pathway, which consequently increased fecundity by promoting vitellogenin synthesis. In the red morph, however, nitrogen fertilization did not change the concentration of essential amino acids, TOR signaling or fecundity. CONCLUSIONSpecific amino acids accumulation and the nutrient transduction pathway in pea aphids are responsible for genotype-specific fecundity in response to nitrogen fertilization, which could be used as potential target for pest control. (c) 2018 Society of Chemical Industry