BackgroundCassava provides over half of the dietary requirement for more than 200 million poor in Africa. In recent years, cassava has been affected by an epidemic of a virus disease called cassava brown streak disease (CBSD) that is spreading in much of eastern and central Africa, affecting food security and the economic development of the poor. The viruses that cause CBSD are transmitted by the insect vector whitefly (Bemisia tabaci), which have increased to very high numbers in some African countries. Strains of endosymbiotic bacteria infecting whiteflies have been reported to interact specifically with different whitefly populations with varied effects on its host biology and efficiency of virus transmission. The main aim of this study was therefore to investigate the prevalence and diversity of the secondary endosymbiotic bacteria infecting cassava whiteflies with a view to better understand their role on insect population dynamics and virus disease epidemics.ResultsThe genetic diversity of field-collected whitefly from Tanzania, Malawi, Uganda and Nigeria was determined by mitochondrial DNA based phylogeny and restriction fragment length polymorphism. Cassava in these countries was infected with five whitefly populations, and each one was infected with different endosymbiotic bacteria. Incidences of Arsenophonus, Rickettsia, Wolbachia and Cardinium varied amongst the populations. Wolbachia was the most predominant symbiont with infection levels varying from 21 to 97%. Infection levels of Arsenophonus varied from 17 to 64% and that of Rickettsia was 0 to 53%. Hamiltonella and Fritschea were absent in all the samples. Multiple locus sequence typing identified four different strains of Wolbachia infecting cassava whiteflies. A common strain of Wolbachia infected the whitefly population Sub-Saharan Africa 1-subgroup 1 (SSA1-SG1) and SSA1-SG2, while others were infected with different strains. Phylogeny based on 16S rDNA of Rickettsia and 23S rDNA of Arsenophonus also identified distinct strains.ConclusionsGenetically diverse bacteria infect cassava whiteflies in Africa with varied prevalence across different host populations, which may affect their whitefly biology. Further studies are required to investigate the role of endosymbionts to better understand the whitefly population dynamics.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0425-5) contains supplementary material, which is available to authorized users.

Many animal and plant viruses depend on arthropods for their transmission. Virus-vector interactions are highly specific, and only one vector or one of a group of vectors from the same family is able to transmit a given virus. Poleroviruses (Luteoviridae) are phloem-restricted RNA plant viruses that are exclusively transmitted by aphids. Multiple aphid-transmitted polerovirus species commonly infect pepper, causing vein yellowing, leaf rolling, and fruit discoloration. Despite low aphid populations, a recent outbreak with such severe symptoms in many bell pepper farms in Israel led to reinvestigation of the disease and its insect vector. Here we report that this outbreak was caused by a new whitefly (Bemisia tabaci)-transmitted polerovirus, which we named Pepper whitefly-borne vein yellows virus (PeWBVYV). PeWBVYV is highly (Ͼ95%) homologous to Pepper vein yellows virus (PeVYV) from Israel and Greece on its 5= end half, while it is homologous to African eggplant yellows virus (AeYV) on its 3= half. Koch's postulates were proven by constructing a PeWBVYV infectious clone causing the pepper disease, which was in turn transmitted to test pepper plants by B. tabaci but not by aphids. PeWBVYV represents the first report of a whitefly-transmitted polerovirus. IMPORTANCE The high specificity of virus-vector interactions limits the possibility of a given virus changing vectors. Our report describes a new virus from a family of viruses strictly transmitted by aphids which is now transmitted by whiteflies (Bemisia tabaci) and not by aphids. This report presents the first description of polerovirus transmission by whiteflies. Whiteflies are highly resistant to insecticides and disperse over long distances, carrying virus inoculum. Thus, the report of such unusual polerovirus transmission by a supervector has extensive implications for the epidemiology of the virus disease, with ramifications concerning the international trade of agricultural commodities.

Citrus greening disease known also as Huanglongbing (HLB) caused by the phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’ (CLas) has resulted in tremendous losses and the death of millions of trees worldwide. CLas is transmitted by the Asian citrus psyllid Diaphorina citri. The closely-related bacteria ‘Candidatus Liberibacter solanacearum’ (CLso), associated with vegetative disorders in carrots, is transmitted by the carrot psyllid Bactericera trigonica. A promising approach to prevent the transmission of these pathogens is to interfere with the vector-pathogen interactions, but our understanding of these processes is limited. It was recently reported that CLas induced changes in the nuclear architecture, and activated programmed cell death, in D. citri midgut cells. Here, we used electron and fluorescent microscopy and show that CLas induces the formation of endoplasmic reticulum (ER)-associated bodies. The bacterium recruits those ER structures into Liberibacter containing vacuoles (LCVs), in which bacterial cells seem to propagate. ER- associated LCV formation was unique to CLas, as we could not detect these bodies in B. trigonica infected with CLso. ER recruitment is hypothesized to generate a safe replicative body to escape cellular immune responses in the insect gut. Understanding the molecular interactions that undelay these responses will open new opportunities for controlling CLas.