Metabolism of amino acids, organic acids and sugars extracted from the xylem fluid of four host plants by adult Homalodisca coagulata

The efficiency of amino acid, organic acid and sugar metabolism was quantified for adult Homalodisca coagulata (Say) (Homoptera: Cicadellidae) by comparing chemical profiles of xylem fluid (food source) and insect exudate. Leafhoppers were confined in Parafilm® sachets to stems of 4 host plants: [Baccharis halimifolia (L.), Lagerstroemia indica (L.), Prunus salicina (Lindl.), Prunus persica (L.), Batsch]. Insect feeding rates (0.09-0.27 ml h−1***), exudate osmolarity (7.8–12.8 mM) and exudate composition (mainly inorganic entities) were characteristic of a xylem feeder. Total organic solute concentration in the xylem fluid of B. halimifolia, L. indica, P. salicina and P. persica was ca. 9.4, 13,8, 5.5 and 1.8 mM, respectively. Nineteen protein amino acids, 7 organic acids and 3 or 4 sugars were identified in the xylem fluid. Total amino acids, organic acids and sugars were metabolized with ca. 99% efficiency. Glutamine, asparagine, arginine and citric, malic and succinic acids, the predominant organic compounds in the xylem fluid of all four plant species, were metabolized with greater than 99% efficiency. Cysteine (51%), methionine (74%) and oxalic acid (77%) were metabolized with the lowest efficiency. The primary nitrogenous waste was NH+4; uric acid or urea were not detected. Nitrogen retention was generally less than 60% of dietary nitrogen. High feeding rates, ammonotelism and an extremely high metabolic efficiency of organic compounds permit H. coagulata to subsist on the dilute and skewed chemical profile of xylem fluid. Resume Metabolisms des acides amines, des acides organiques et des sucres extraits de la seve du xyleme de quatre plantes-hotes par Homalodisca coagulata L'efficacite du metabolisme des amino-acides, des acides organiques et des sucres a ete quantifiee chez des H. coagulata Say (Ho***rn. Cicadellidae) adultes, en comparant la composition chimique de la seve du xyleme et du miellat des insectes. Les cicadelles ont ete maintenues dans des sachets de parafilm avec des tiges de 4 plantes hotes: Baccharis halimifolia L., Lagerstroemia indica L., Prunus salicina Lindl. et Prunus persica Batsch. Le taux de consommation (0,09 a 0,27 ml hr−1, l'osmolarite du miellat (7,8 a 12,8 mM) et la composition du miellat (principalement des elements inorganiques) sont caracteristiques des consommateurs de xyleme. Les concentrations organiques totales en solute de la seve du xyleme etaient respectivement: 9,4; 13,8; 5,5; et 1,8 mM chez B. halimifolia, L. indica, P. salicina et P. persica. 19 amino acides proteiques, 7 acides organiques et 3 ou 4 sucres ont ete identifies dans la seve du xyleme. Les acides amines, les acides organiques et les sucres ont ete metabolises dans leur ensemble avec une efficacite de 99%. La glutamine, l'asparagine, l'arginine et les acides citrique, malique et succinique, - les principaux composes organiques de la seve du xyleme de ces 4 plantes, - ont ete metabolises avec plus de 99% d'efficacite. La cysteine (51%), la methionine (74%) et l'acide oxalique (77%) ont ete metabolises avec une plus faible efficacite. Le dechet azote primarie etait NH+4; l'acide urique et luree n'ont pas ete deceles. La fixation d'azote a ete generalement inferieure a 60% de l'azote consomme. Des taux de consommation eleves, l'ammonotelisme et une efficacite extremement elevee du metabolisme des composes organiques permettent a H. coagulata de survivre malgre la composition chimique biaisee et la dilution de la seve du xyleme.