Biology, morphometrics and analyses of non-specific esterases were carried out for populations of Bemisia tabaci (Gennadius) collected from leucaena [Leucaena leucocephala (Lam.) de Wit] in New Delhi, India and compared with those for cotton populations. The developmental periods of the egg, and the first to fourth instars of the leucaena populations were 6.7 ± 0.18, 4.2 ± 0.18, 3.8 ± 0.14, 3.0 ± 0.0 and 5.2 ± 0.18 days, respectively, with a total life-cycle duration of 22.9 ± 0.58 days; fecundity (62.60 ± 61.53 eggs per female) and longevity (male: 13.50 ± 0.12 days, female: 16.50 ± 0.12 days) were higher than those recorded for the cotton population, with a sex ratio (male:female) of 1:3.7 in cotton and 1:4 in leucaena. Morphometrics revealed significant differences in the length of egg, second, third and fourth instars (P < 0.05). Of the 62 measurements of the puparia analysed, 70% of those of the head, 44% of those of the thorax and 51% of those of the abdomen showed significant differences between the cotton and leucaena populations. Mapping of the host association of samples onto principal component ordination showed their significant separation according to host plants, with the first three principal components accounting for 66% of the total variation. The analysis of non-specific esterases showed two bands at Rm E0.18 and E0.23 in the cotton populations but not in the leucaena populations. So far, B. tabaci is known on leucaena only from Taiwan. The present study reports it as a new host record from India in addition to documenting the biology, morphometrics and esterases of this and a cotton population.