DEMONSTRATION AND PRELIMINARY CHARACTERIZATION OF ALPHA-AMYLASE IN THE SWEET-POTATO WHITEFLY, BEMISIA-TABACI (ALEYRODIDAE, HOMOPTERA)

An alpha-amylase that hydrolyzes unmodified starch or amylopectin azure was demonstrated in crude and partially purified extracts prepared from whole carcasses of sweetpotato whiteflies (SPW) (Bemisia tabaci Genn.). All nymphal instars and adult SPW, including newly eclosed crawlers that had not yet fed on plant materials, were found to have active alpha-amylase. alpha-Amylase activity per mg protein was greatest in 1st instars and decreased with age up to the ''pupal'' stage, with a very slight increase in activity in adults. However, activity per individual did not differ substantially as a function of age. The alpha-amylase had an apparent molecular weight of about 70 kDa, an isoelectric point of 6.32 and eluted with about 250 mM NaCl from a strongly basic anion-exchange column. The enzyme activity was inhibited by EDTA and not activated by either NaCl or KNO3. CaCl2 strongly enhanced activity. alpha-Amylase activity was greatest at pH 7.0, but there was considerable activity at pHs above 7.0. The K-m of the alpha-amylase was 1.47 Mm with p-nitrophenyl alpha-D-malto-heptaoside as substrate. The presence of an amylolytic enzyme in a phloem-feeding insect is unexpected and raises questions about current assumptions of feeding behavior of this species.