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

Populations of the whitefly, Bemisia tabaci collected from the Americas 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. Esterase markers were used to detect polymorphisms among regional B. tabaci populations and to establish the present distribution of B. tabaci biotypes in the region. The A biotype occurred only in contiguous locales in northern Mexico and the southwestern US, while the B biotype was present throughout much of the Caribbean Basin and the US, and in Brazil. Distinct C and D type esterase markers were observed for Costa Rican 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 almost equally sensitive to an organophosphate, profenofos. The B biotype was more resistant to a pyrethroid, permethrin, suggesting the existence of a biotype of B. tabaci, with a history of exposure to pesticides with a pyrethroid-based chemistry. In mating studies involving reciprocal crosses between the A and the B biotypes, very few F1 female progeny were produced, indicating either minimal or non-existent reproductive 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 locations.