Submitted to: National Research and Action Plan for Silver Leaf Whitefly
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 1998
Publication Date: N/A
The silverleaf whitefly accumulated high levels of sorbitol in its hemolymph in a diurnal pattern. The greatest sorbitol concentrations in the hemolymph were found in the early afternoon in insects collected from fields of upland cotton. Hemolymph concentrations during early morning hours were found to be approximately 10-fold lower than in the early afternoon. In laboratory and greenhouse experiments, elevated temperature stimulated this polyol accumulation. Assay of enzymes extracted from adult insects showed that hemolymph sorbitol was produced from fructose by an unusual ketose reductase. Other insect systems such as the silkworm synthesize sorbitol during diapause from glucose originating from glycogen using an aldose reductase. At the end of diapause, such insects convert accumulated sorbitol to fructose. We could not detect interconversion of glucose and sorbitol in B. argentifolii. We found only traces of sorbitol in the honeydew of this insect. This suggests that at the end of the day when sorbitol in the hemolymph decreased, sorbitol was converted back to fructose rather than being excreted. Insects living upon water-stressed plants had greater levels of hemolymph sorbitol than insects on well- watered plants. Insects were also much more resistant to high temperature when allowed to feed and accumulate sorbitol, than those prevented from feeding. This suggests that sorbitol accumulation in this insect is a physiological adaptation for survival in its hot, dry environment.