Elevated free amino acids in plant phloem sap fuel aphid growth and reproduction. Green peach aphids fed 50% of normal amino acids showed major drops in weight and fecundity. Nitrogen availability, especially free amino acids, is the limiting nutrient that drives pest outbreaks and host-plant selection.
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What is the first thing you think when you see pests attacking your crop? I'm trying to convince you that the first thing you should think is, could the amino acids in the plant sap be too high and producing an abundant food source for them to eat? I have plenty of review articles and studies to share with you to back this up, so let's get into it. It is well accepted that the supply of nitrogen in the form of free amino acids is a limiting factor in the aphid diet for growth and fecundity. Aphids generally rely on nitrogen-containing amino acids, which only occur in low concentrations in phloem sap. Both nymphs and adults were rarely found on the no amino acids diet. The no amino acids diet seems to be unnatural, as it is unlikely that plant phloem sap is completely devoid of amino acids. However, very low availability of amino acids may occur, for example, when plants are highly nutrient limited, free amino acids are rapidly unloaded from the phloem, or when other factors reduce the availability of free amino acids. Free amino acids in the phloem sap are the dominant nitrogen source for aphids, but their availability is usually poor. Here we examine the performance of the green peach aphid fed a standard diet or a diet containing 50% of the total amino acids of the control diet. Aphid weight and fecundity were significantly reduced in the half diet group. Availability of nitrogen as a nutrient source in plants generally limits the performance of phytophagous insects. Amino acids in plant phloem sap are the dominant dietary nitrogen source for phloem-feeding Hemipterans. Nutritional quality of plant tissue is one of the main characteristics of host plant selection by phytophagous Insects. Nitrogen is the major nutrient required by insects and in most cases the main limiting factor for optimal growth of insects. One of the most reliable generalizations in all of ecology is that differences in insect performance, i.e., in growth, survivorship, and sometimes even fecundity, depend on differences in the nitrogen and water content of host plant tissue. The distinction between free amino acids and those in proteins may be important for insects that are physiologically incapable of ingesting large peptides.
