IDENTIFICATION OF THE POINSETTIA STRAIN OF BEMISIA-TABACI (HOMOPTERA, ALEYRODIDAE) ON BROCCOLI BY ELECTROPHORESIS

The sudden occurrence of sweetpotato whitefly, Bemisia tabaci (Gennadius), on cruciferous crops in southern California prompted investigation into the basis for the apparent expansion in host range of this species. Isoelectric focusing (IEF) procedures were used to determine the allozymic variation among whiteflies collected from broccoli, poinsettia, and cotton. Tentative interpretation of the IEF banding patterns in terms of allelic variation at 18 loci encompassing 14 enzymes were made. Six of the loci were polymorphic and, at each polymorphic locus, the cotton strain had one or more unique alleles. In contrast, whiteflies collected from broccoli and poinsettia were identical in terms of the presence or absence of alleles at each of the 18 loci. These results suggest that whiteflies from broccoli and poinsettia recently derived from the same source. In corroborative experiments, whiteflies collected from broccoli and reared on mustard produced squash silverleaf symptoms as did whiteflies reared on poinsettia but the cotton strain did not. These data verify the occurrence of the poinsettia strain of B. tabaci in southern California agricultural areas. The implications of this introduction on virus epidemiology and crop production in the area are discussed.