REGIONAL DISTRIBUTION, INSECTICIDE RESISTANCE, AND RECIPROCAL CROSSESBETWEEN THE A-BIOTYPE AND B-BIOTYPE OF BEMISIA-TABACI

Populations of the whitefly, Bemisia tabaci collected from the America s and the Caribbean Basin were examined for non-specific esterases and for the ability to induce characteristic phytotoxic disorders in key assay species as a means of investigating biogeographic diversity. Est erase markers were used to detect polymorphisms among regional B. taba ci populations and to establish the present distribution of B. tabaci biotypes in the region. The A biotype occurred only in contiguous loca les in northern Mexico and the southwestern US, while the B biotype wa s present throughout much of the Caribbean Basin and the US, and in Br azil. Distinct C and D type esterase markers were observed for Costa R ican and Nicaraguan B. tabaci populations, respectively. The 0 or null type population was collected only from Jatropha gossypifolia (L.) in Puerto Rico. Laboratory colonies of the A and the B biotypes were alm ost equally sensitive to an organophosphate, profenofos. The B biotype was more resistant to a pyrethroid, permethrin, suggesting the existe nce of a biotype of B. tabaci, with a history of exposure to pesticide s with a pyrethroid-based chemistry. In mating studies involving recip rocal crosses between the A and the B biotypes, very few F1 female pro geny were produced, indicating either minimal or non-existent reproduc tive compatibility between these haplo-diploid B. tabaci populations, presently considered to be the same species. Evidence is presented for the recent and widespread introduction, and subsequent spread of the B biotype throughout the US, the Caribbean Basin, and other proximal l ocations.