Vector-Virus Mutualism Accelerates Population Increase of an Invasive Whitefly

The relationships between plant viruses, their herbivore vectors and host plants can be beneficial, neutral, or antagonistic, depending on the species involved. This variation in relationships may affect the process of biological invasion and the displacement of indigenous species by invaders when the invasive and indigenous organisms occur with niche overlap but differ in the interactions. The notorious invasive B biotype of the whitefly complex Bemisia tabaci entered China in the late 1990s and is now the predominant or only biotype in many regions of the country. Tobacco curly shoot virus (TbCSV) and Tomato yellow leaf curl China virus (TYLCCNV) are two whitefly-transmitted begomoviruses that have become widespread recently in south China. We compared the performance of the invasive B and indigenous ZHJ1 whitefly biotypes on healthy, TbCSV-infected and TYLCCNV-infected tobacco plants. Compared to its performance on healthy plants, the invasive B biotype increased its fecundity and longevity by 12 and 6 fold when feeding on TbCSV-infected plants, and by 18 and 7 fold when feeding on TYLCCNV-infected plants. Population density of the B biotype on TbCSV- and TYLCCNV-infected plants reached 2 and 13 times that on healthy plants respectively in 56 days. In contrast, the indigenous ZHJ1 performed similarly on healthy and virus-infected plants. Virus-infection status of the whiteflies per se of both biotypes showed limited effects on performance of vectors on cotton, a nonhost plant of the viruses. The indirect mutualism between the B biotype whitefly and these viruses via their host plants, and the apparent lack of such mutualism for the indigenous whitefly, may contribute to the ability of the B whitefly biotype to invade, the displacement of indigenous whiteflies, and the disease pandemics of the viruses associated with this vector

Factors Affecting Population Dynamics of Maternally Transmitted Endosymbionts in Bemisia tabaci

While every individual of Bemisia tabaci (Hemiptera: Aleyrodidae) harbors the primary symbiont (P-symbiont) Portiera, the infection frequencies of the six secondary symbionts (S-symbionts) including Hamiltonella, Arsenophonus, Cardinium, Wolbachia, Rickettsia and Fritschea vary greatly among different populations. To characterize the factors influencing the infection dynamics of the six S-symbionts in B. tabaci, gene-specific PCR were conducted to screen for the presence of the P-symbiont Portiera and the six S-symbionts in 61 (17 B and 44 Q biotypes) field populations collected from different plant species and locations in China. All individuals of the 61 populations hosted the P-symbiont Portiera, but none of them harbored Arsenophonus and Fritschea. The presence and infection rates of Hamiltonella, Cardinium, Rickettsia, Wolbachia and their co-infections Rickettsia + Hamiltonella (RH), Rickettsia + Cardinium (RC), Hamiltonella + Cardinium (HC) and Rickettsia + Hamiltonella + Cardinium (RHC) varied significantly among the 61 field populations; and the observed variations can be explained by biotypes, sexes, host plants and geographical locations of these field populations. Taken together, at least three factors including biotype, host plant and geographical location affect the infection dynamics of S-symbionts in B. tabaci

Occurrence of three genotypic clusters of Bemisia tabaci and the rapid spread of the B biotype in south India

The whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), is generally considered to have originated from the Indian subcontinent, although little information has so far been collected on the molecular diversity of populations present in this region. The genetic diversity of B. tabaci populations from Karnataka State, south India was analysed using the random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) technique and partial mitochondrial cytochrome oxidase I (mtCOI) gene sequences (689 bases) of 22 selected samples. A total of 108 whitefly samples analysed by RAPD-PCR produced 89 polymorphic bands, and cluster analyses grouped them according to their geographic origin into ‘north’ and ‘south’ Karnataka. Phylogenetic analysis of mtCOI gene sequences with reference B. tabaci sequences from other Asian countries divided them into three genotypic clusters. Each cluster was supported with high bootstrap values (82–100%) and the individuals belonging to each cluster shared high nucleotide identities (up to 100%). This indicated at least three distinct genotypes, apparently indigenous to India, which are also present in China, Malaysia, Nepal, Pakistan, and Thailand. These coexist with the B biotype, which was first reported in India in 1999, and has since spread rapidly to other states in south India. The B biotype was more common than the indigenous B. tabaci, in locations where it had been present for more than 2 years. This is reminiscent of the situation in the Americas during the early 1990s, where the B biotype replaced existing biotypes and caused unprecedented losses to agriculture