Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 1, 1997
Publication Date: N/A
Interpretive Summary: The silverleaf whitefly (Bemisia argentifolii) is a serious pest, causing severe damage to a variety of crop species including cotton. Whiteflies feed on the conductive-tissue of plants deriving nutrition from the sugars and amino acids from the plant sap. Because of the high sugar content of plant sap, sugar is in excess and some must be excreted in the form of a sugary mixture called honeydew. In this study we examined the effect of sucrose concentration on its uptake and metabolism by the silverleaf whitefly. Sucrose is the only sugar present in the phloem sap of cotton. Our results showed that when the sucrose concentration was limiting the whiteflies broke sucrose down to smaller units to use for its metabolism. However, when sucrose was in excess, the whiteflies converted it to an unusual sugar called trehalulose. These results indicate that the synthesis of trehalulose by the whitefly plays an essential role in maintaining proper metabolic activity on a high sucrose diet. This conclusion is important for efforts to control this insect pest for they indicate that inhibiting trehalulose synthesis is a possible strategy for controlling silverleaf whitefly on species like cotton.
Technical Abstract: Uptake and metabolism of sucrose by silverleaf whiteflies (Bemisia argentifolii) was investigated on diets containing 3 to 30% sucrose. At an optimal pH of 7, the volume of liquid ingested decreased with increasing dietary sucrose concentration, but the amount of sucrose ingested increased. Above a dietary sucrose concentration of 10%, a greater amount of the ingested carbon was excreted by than was retained, and the proportion that was excreted increased with increaasing dietary sucrose concentration. Carbohydrate analysis showed that the composition of excreted honeydew changed from predominantly glucose and fructose at low dietary sucrose concentrations to mainly trehalulose at high concentrations, with little change in the proportion of larger oligosaccharides. Measurements of trehalulose synthase and sucrase revealed that the enzymatic potential for metabolizing sucrose shifts from favoring sucrose hydrolysis at low sucrose concentrations to sucrose isomerization at high sucrose concentrations. Thus, trehalulose levels in the whitefly are directly related to the properties of trehalulose synthase and sucrase and the concentration of sucrose in the diet. We propose that trehalulose is synthesized for excretion when the carbon input from sucrose is in excess of metabolis needs.