EFFECT OF SUCROSE CONCENTRATION ON CARBOHYDRATE-METABOLISM IN BEMISIA-ARGENTIFOLII - BIOCHEMICAL-MECHANISM AND PHYSIOLOGICAL-ROLE FOR TREHALULOSE SYNTHESIS IN THE SILVERLEAF WHITEFLY

Uptake and metabolism of sucrose by adult silverleaf whiteflies (Bemis ia argentifolii) were investigated on defined diets containing sucrose concentrations from 3 to 30% (w/v), At an optimal pH of 7, the volume of liquid ingested decreased with increasing dietary sucrose concentr ation, but the amount of sucrose ingested showed a net increase, Above a dietary sucrose concentration of about 10%, a greater amount of the ingested carbon was excreted by the whiteflies than was retained, and the proportion that was excreted increased progressively with increas ing dietary sucrose concentration, Carbohydrate analysis showed that t he composition of excreted honeydew changed from predominantly glucose and fructose at low dietary sucrose concentrations to predominantly t rehalulose at high concentrations, with little change in the proportio n of larger oligosaccharides. Measurements of whitefly trehalulose syn thase and sucrase activities revealed that the enzymatic potential for metabolizing sucrose shifted from favoring sucrose hydrolysis at low sucrose concentrations to sucrose isomerization at high sucrose concen trations, Thus, the amount of trehalulose synthesized by the silverlea f whitefly was directly related to the properties of trehalulose synth ase and sucrase and the concentration of sucrose in the diet, We propo se that trehalulose is synthesized for excretion when the carbon input from sucrose is in excess of metabolic needs.