BIOCHEMICAL-CHARACTERIZATION OF BIOTYPE-SPECIFIC ESTERASES IN THE WHITEFLY, BEMISIA-TABACI GENN (HOMOPTERA, ALEYRODIDAE)

Biochemical properties of the predominant esterases found in two disti nct populations, presently considered to be different biotypes of the whitefly Bemisia tabaci, were investigated. General esterases, previou sly established as diagnostic markers on native polyacrylamide gels (P AGE) for the 'A' and 'B' biotypes, were characterized with respect to molecular masses, isoelectric points (pIs), isomeric relationships, an d substrate specificities. One previously unidentified band in the 'B' biotype was detected on native gels when ethylenediaminetetracetic ac id (EDTA) was added to gel buffers. In each of the (A' and 'B' biotype s, 12 bands were resolved by isoelectric focusing (IEF),and had pIs ra nging from 4.86 to 7.37, and 4.70 to 6.59, respectively. The two bands ('B'1 and 'B'2), used as diagnostic markers on native gels for the 'B ' biotype, were identified as a single band (E7) with IEF. An analogou s E7 band was resolved in the 'A' biotype with IEF, but corresponded t o only one isomer (A6) on native gels. Results of substrate studies re vealed most bands on IEF gels had carboxylesterase activity. The E7 es terase in each biotype was identified specifically as acetylcholineste rase (AChE). Ferguson plots revealed these E7 esterases of the 'A' and 'B' biotypes had equivalent charges, but different molecular masses, indicating they are size isomers. Two dimensional (2D) and IEF analyse s confirmed this relationship.