Amino acids as determinants of host preference for the xylem feeding leafhopper, Homalodisca coagulata (Homoptera: Cicadellidae)

Abstract

Homalodisca coagulata is a highly polyphagous xylem feeder with distinct seasonal patterns in it's selection of host plants. These patterns were examined in relation to the amino acid content of the xylem for four common host species; Lagerstroemia indica, Baccharis halimifolia, Prunus persica, and Prunus salicina. Xylem fluid was collected from each host species at times when numbers of feeding leafhoppers were both low and high. In each case, concentrations of amino acids were greatest when numbers were high. Similarly, comparisons between host species at given times showed that concentrations of amino acids were positively correlated with host selection. In a second study, amino acids of xylem were manipulated by budding scions of a non-preferred host (P. persica) on rootstocks of preferred (P. salinica) and non-preferred (P. persica) hosts. Morphology and phenology of the budded trees were similar to that of the scion species yet the xylem composition of amino acids was primarily dependent on the rootstock. Concentrations of amino acids and the preference of leafhoppers were roughly two-fold greater for scions of the preferred than the non-preferred rootstock. In both studies, amides (glutamine plus asparagine) were the amino acids most highly correlated with host selection. These compounds are the predominant amino acids in xylem fluid, have high nitrogen to carbon ratios, and account for a high percentage of the caloric value in xylem fluid. Many of the less abundant amino acids were positively correlated with host preference, but the correlations were less consistent and correlation coefficients were generally lower.

Bottom-up effects of host plant nutritional quality on Plutella xylostella (Lepidoptera: Plutellidae) and top-down effects of herbivore attack on plant compensatory ability

“…10% total nitrogen dry weight basis), which does not accord with earlier reports of low nitrogen levels resulting in poor larval survival (Myers & Post, 1981;Myers, 1985;Cates et al, 1987). Increased levels of nitrogen and other nutrients can lead to unbalanced amino acid profiles and high concentrations of organic acids in plant tissues (Williams & Cronin, 2004); consequently such diets can be detrimental and even toxic to insects (Reese, 1979;Brodbeck et al, 1990). Similar to our results, significantly fewer L. tityrus developing on plants growing in soils that had been treated with a nitrogenous fertilizer survived than on plants growing in un-fertilized soil (Fischer & Fiedler, 2000).…”

Swapping symbionts in spittlebugs: evolutionary replacement of a reduced genome symbiont

“…Genes underlying steps in the TCA cycle are retained, indicating capability for producing energy from carbon skeletons derived from sugar or from amino-acid catabolism. Xylem sap lacks sugar, and amino acids are the primary energy substrates available for use by xylem-feeding insects (Brodbeck et al, 1990). We hypothesize that the Sulcia-encoded glutamate dehydrogenase (GdhA) enables the generation of 2-oxoglutarate from glutamate and that this enters the SLs-PSPU as a substrate in the TCA cycle, providing a major source of ATP for the symbiotic system (Figure 3b).…”

“…We hypothesize that the Sulcia-encoded glutamate dehydrogenase (GdhA) enables the generation of 2-oxoglutarate from glutamate and that this enters the SLs-PSPU as a substrate in the TCA cycle, providing a major source of ATP for the symbiotic system (Figure 3b). This possibility would depend on availability of excess glutamate, while glutamine and asparagine comprise most amino acids in the xylem (Brodbeck et al, 1990). Glutamate could be provided by SLs PSPU, which retains intact gltBD, encoding glutamate synthase, the enzyme that catalyzes the production of glutamate from glutamine.…”

“…P. spumarius ingests the main transpiration xylem stream from a variety of plant species and prefers plants with high aminoacid content in the xylem fluid (Wiegert, 1964;Horsfield, 1977;Hoffman and McEvoy, 1985;Malone et al, 1999). This diet lacks not only essential amino acids but also sugar or other abundant energy substrates; nonessential amino acids, primarily glutamine and asparagine, contain the primary energy content (Brodbeck et al, 1990). Energy demands are heightened further, because xylem is under strong negative pressure in plant shoots (Raven et al, 2005), and P. spumarius must use powerful muscles to extract its food.…”

Effects of elevated CO2 on the nutrient compositions and enzymes activities of Nilaparvata lugens nymphs fed on rice plants

“…Brodbeck et al [23] reported that the total amino acid content in the xylem strongly correlated with the survival and development rates of xylem-feeding insects.…”