Colonization of non-cassava plant species by cassava whiteflies (Bemisia tabaci) in Uganda

Bemisia tabaci(Genn.) (Homoptera: Aleyrodidae) is the vector of cassava mosaic geminiviruses (CMGs), which are the main production constraint to cassava [Manihot esculenta Crantz (Euphorbiaceae)],both in Uganda and elsewhere in Africa. TwoB. tabaci genotype clusters, Ug1 and Ug2, differentiated at 8% nucleotide (nt) divergence within the mitochondrial cytochrome oxidase I (mtCOI) gene, have been shown to occur on cassava in Uganda. However, the role of alternative hosts in the ecology of cassavaB. tabaci genotypes and their possible involvement in the epidemiology of cassava mosaic disease (CMD) in Uganda remain unknown. In this study, we investigated the restriction of cassava B. tabaci genotypes to cassava and the colonization of alternative host species in select cassava-growing areas of the country in 2003 and 2004. Bemisia tabaci adults and 4th instar nymphs were collected from cassava and 11 other cultivated and uncultivated species occurring adjacent to the sampled cassava fields Phylogenetic analysis of mtCOI sequences revealed that only a single genotype cluster, Ug1, was present on both cassava and non-cassava plant species sampled in this study. The Ug1 genotypes (n = 49) shared 97–99% nt identity with the previously described cassava-associated B. tabaci populations in southern Africa, and were ∼ 8% and ∼ 13% divergent from Ug2 and the ‘Ivory Coast cassava’ genotypes in Uganda and Ivory Coast, respectively. The Ug1 genotypes occurred (as adults) on all 12 source-plant species sampled. However, based on the presence of B. tabaci 4th instar nymphs, the Ug1 genotypes (n = 13) colonized cassava and five other non-cassava plant species: Manihot glaziovii, Jatropha gossypifolia, Euphorbia heterophylla, Aspilia africana, and Abelmoschus esculentus, suggesting that cassava B. tabaci (Ug1 genotypes) are not restricted to cassava in Uganda. No Ug2-like genotypes were detected on any of the plant species sampled, including cassava, in this study. The identification of additional hosts for at least one genotype cluster, Ug1, known also to colonize cassava, and which was hitherto thought to be ‘cassava-restricted’ may have important epidemiological significance for the spread of CMGs in Uganda

Phylogenetic analysis of Bemisia tabaci (Hemiptera: Aleyrodidae) populations from cotton plants in Pakistan, China, and Egypt

Bemisia tabaci is a species complex, of which the B and Q biotypes are globally distributed. B. tabaci feeds on more than 600 plant species including cotton, which is one of the main crops in Pakistan. In this study, the biotypes/haplotypes of B. tabaci populations collected from cotton plants in Pakistan, China, and Egypt were identified, and their phylogenetic relationships were investigated. None of the populations from Pakistan or Egypt belonged to the B or Q biotype: all 16 samples from Pakistan belonged to haplotype “PCG-1” and it is a group of unresolved populations all from Pakistan, while all three populations from Egypt belonged to unresolved haplotype “ECG.” The three populations from China belonged to the B biotype. Phylogenetic analysis indicated that the PCG-1, ECG, and B biotypes clustered into different clades even though they share the same cotton plant species as their host. The association between the outbreaks of cotton leaf curl disease and the occurrence of the PCG haplotype of B. tabaci in Pakistan is discussed