Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: June 1, 1998
Publication Date: N/A
Technical Abstract: The polyhydroxy alcohol, mannitol, was identified in the body of the cotton aphid. It accumulated in the bodies of aphids during the course of the day, analagous to the previously reported accumulation of sorbitol in the silverleaf whitefly. Polyol synthesis was stimulated by elevated temperatures. Hemolymph polyol during mid afternoon in these insects reached approximately 500 mM. The enzyme catalyzing this reaction, an NADP(H)-dependent ketose reductase/mannitol dehydrogenase, is analagous to the NADP(H)-dependent ketose reductase previously shown to produce sorbitol from fructose in SLW. We did not find evidence of a glucose to sorbitol interconversion in whiteflies, and whitefly honeydew was found to contain only traces of this polyol. Cotton aphid honeydew did not contain mannitol. Glucose was not converted to mannitol by aphid extracts in the presence of either NADH or NADPH. This suggests that in both insects polyols are converted back to fructose during periods when hemolymph concentrations decrease. SLW living on water-stressed plants accumulated higher concentrations of sorbitol than those on well-watered plants. SLW which were allowed to feed and thereby accumulate sorbitol were more resistant to elevated temperatures than those prevented from feeding. These results suggest that polyol accumulation in these insects is a physiological adaptation for their survival in hot, dry environments.