SPATIAL AND TEMPORAL GENETIC-VARIATION IN POPULATIONS OF THE WHITEFLY BEMISIA-TABACI (GENN) IN ISRAEL AND COLOMBIA - AN INTERIM-REPORT

Intensive investigations of genetic variation within and among populations of the whitefly, Bemisia tabaci, are under way in Israel and in Colombia. A polymorphic esterase (EST), which seems to be controlled by a Mendelian locus, has two alleles in sufficiently high frequencies to be useful as a genetic marker. The analysis of more than 10,000 individual adult whiteflies shows genetic differences among localities in the frequencies of the fast (F) and slow (S) alleles. These differences seem to be related to the intensity of insecticide use against the whitefly. The frequency of F is high in unsprayed areas and in control laboratory populations, but is close to zero in heavily-sprayed agricultural areas. The frequency of Fon cotton in agricultural areas is high in winter and spring, but decreases dramatically in the summer (coincidental with the onset of pest-control activities on cotton). A similar temporal pattern on untreated Lantana may be due to migration of adults from agricultural fields. There was no indication of differentiation of populations on different host plants. In Colombia, the difference in EST patterns in different States are very pronounced, suggestive of geographical races. Small samples from Florida, California and Kenya indicate that B. tabaci in different countries may be genetically distinct.