Plant resistance to the B and Q biotypes of sweetpotato whitefly, Bemisa tabaci (Gennadius), induced by benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester (BTH or acibenzolar-S-methyl) in tomato ‘Marmande’ plants was evaluated in free-choice and no-choice assays under different conditions. BTH is the active ingredient of the Syngenta plant activator Bion. BTH treatment affected host preference of B. tabaci (B and Q biotypes) adults on plants sprayed with Bion at 0.2 and 0.4 g/liter during the earlier days of free-choice assays. As a consequence, a decrease in the total number of eggs (although female fecundity was not affected) and in the final number of pupae and empty pupal cases was observed. The effect produced by BTH applied at 0.1 g/liter Bion was not significant. In no-choice assays, a reduction of the numbers of first-stage larvae and total individuals and a delay in insect development were observed when local treatment was restricted to one leaflet per plant, 5 d before B. tabaci (biotype B) infestation. This acquired resistance induced by BTH seemed to be locally expressed because of the differences between treated and nontreated leaflets in the same plants, whereas no differences in nontreated leaflets were observed between BTH-treated and control plants.