POLYOL METABOLISM IN HOMOPTERANS AT HIGH-TEMPERATURES - ACCUMULATION OF MANNITOL IN APHIDS (APHIDIDAE, HOMOPTERA) AND SORBITOL IN WHITEFLIES (ALEYRODIDAE, HOMOPTERA)

Examination of four species of aphid and four of whitefly showed that mannitol was present in each species of aphid, while sorbitol was pres ent in the whitefly species. In the cotton aphid, Aphis gossypii Glove r, the total body content of mannitol was considerably higher at noon than during the early morning. A similar increase in the sorbitol cont ent of the silverleaf whitefly, Bemisia argentifolii Bellows and Perri ng, was also demonstrated. In both species, polyol synthesis is stimul ated by elevated temperatures. Enzyme assays were used to show that fr uctose is the substrate for mannitol synthesis in A. gossypii. The enz yme catalyzing this reaction, an NADP(H)-dependent ketose reductase/ma nnitol dehydrogenase, is analogous to the NADP(H)-dependent ketose red uctase/sorbitol dehydrogenase that produces sorbitol in whiteflies. We stern blot analysis verified that A. gossypii does not contain a prote in that cross-reacts with antibodies against B. argentifolli NADP(H)-d ependent ketose reductase/sorbitol dehydrogenase, whereas the greenhou se whitefly, Trialeurodes vaporariorum Westwood, does. Analysis of sug ars in honeydew from aphids and whiteflies showed that the sugars in t he excrement from these insects are very different from the sugars pre sent in their bodies. Only small amounts of mannitol and sorbitol are excreted in the honeydew from these insects. Sorbitol accumulation pro vides a mechanism for thermo- and osmoprotection in whiteflies. Mannit ol appears to function in a similar capacity in aphids. (C) 1998 Elsev ier Science Inc. All rights reserved.