The Bemisia tabaci (Genn.) complex (Brown et al. 1995b) is a hemipteran (Aleyrodidae) pest that feeds on plant phloem. It also is the most important vector worldwide of several genera of plant virus (Brown 2000, Brown 2001; Brown & Bird 1992).

Bemesia tabaci is best described as a species complex that comprises an unexpectedly large number of genetically variable populations, some of which are discernible owing to distinct phenotypes (Brown et al. 1995a, Brown et al. 1995b). Well-studied B. tabaci populations that have been differentiated are referred to as races (Brown & Bird 1992) or biotypes (Brown et al. 1995a; Costa & Brown 1991). The B biotype (Costa & Brown 1991) is a particularly aggressive B. tabaci variant. It has an extremely broad host range, is highly fecund, and disperses relatively long distances (Brown 2000; Brown et al. 1995b), and has become established in many locations beginning approximately in 1988-present (Costa & Brown 1991; Costa et al. 1993). Since that time, it has been of considerable concern as a pest and virus vector in subtropical and temperate, mild climate zones where the majority of the world's vegetable and fiber crops are produced (Brown et al. 1995a, Brown et al. 1995b; Brown 2000). Population genetics studies have shown that the B biotype probably originated from the Middle Eastern/North African region (Frohlich et al. 1999).

In China B. tabaci has become an important agricultural pest in the late 1990s (Chu et al. 2004; Zhang 2000), and the introduction of the B biotype into China was first reported in 2002 (Luo et al. 2002). The B biotype is now known to be widespread in a number of provinces in China where vegetables, cotton, and ornamentals are produced (Chu et al. 2004; Wu et al. 2003; this report).

In China and elsewhere, the understanding that B. tabaci is a polymorphic, cryptic species that can upsurge without warning and cause great damage to crop and ornamental species is lacking. This has often resulted in the delayed recognition of upsurges in local whitefly populations and/or of exotic introductions (Reitz & Trumble 2002), such as the B biotype. This realization has prompted an accelerated interest in practicing routine monitoring of B. tabaci populations to detect early the potentially invasive B. tabaci, or otherwise upsurgent haplotypes, with particular emphasis on those that are associated with the global commercial plant industry.

The purpose of this study was to determine if the Q biotype (Costa et al. 1993; Guirao et al. 1997) was present in ornamentals and/or annual flowering or bedding plants in China. Such knowledge is important because the Q biotype has only recently been recognized as a potentially invasive pest species in the vegetable and ornamentals industries in the Mediterranean/Middle Eastern region (Guirao et al. 1997; Horowitz et al. 2003). The introduction and establishment of the Q biotype is anticipated, or was possibly expected to already have occurred, in at least certain locations, and is expected to have important and far-reaching economic relevance. The potential for damage will further be exacerbated if Q biotype populations exhibit resistance to a well-known neonicotinoid (Nauen et al. 2002; Rauche & Nauen 2003), upon which the industry presently relies to control B. tabaci. Resistance to this compound has already been reported in Spain and Israel (Ebert & Nauen 2000; Rauche & Nauen 2003).

Recent studies have demonstrated that the mitochondrial cytochrome oxidase I (mtCOI) gene (Brown 2001; Brown et al. 1995b; Frohlich et al. 1999) is a highly informative coding sequence for differentiating populations and haplotypes/biotypes in the B. tabaci complex. In this study, the mtCOI was used as a population genetics marker to detect the presence of and identify the Q biotype, and subsequently to determine its partial distribution in a number of provinces in China, which routinely produce ornamental and bedding plants. Phylogenetic analysis of the mitochondrial COI sequence for B. tabaci collections from China revealed for the first time that the Q biotype is distributed in multiple locations throughout the country.

Materials and Methods

Results

Discussion

Recently, the Q biotype of B. tabaci, which had been a relatively benign pest in the Mediterranean region (Simón et al. 1999), has been recognized as a serious pest and virus vector, owing to its ability to reach high population densities (Moya et al. 2001; Simón et al. 1999) and to develop resistance to at least one neonicotinoid (Rauch & Nauen 2003). These characteristics have been noted together with an increase in Q biotype infestations in southern Spain, where the B biotype is now almost absent, despite its introduction there in the mid-1990s (Simón et al. 1999). What is now recognized as the Q biotype has been identified in the Iberian Peninsula, in Sardinia and Sicily, and in Morocco (Brown 2000; Moya et al. 2001), the general region (Mediterranean/Middle East/North Africa) to which Q-like haplotypes are thought to be indigenous (Brown 2000).

Significant differences in host suitability (Muniz 2000) and developmental parameters (Muniz & Nombela 2001) for the B and Q biotypes, with respect to four weed species that occur in the winter months, were determined in no-choice assays. Except for Lactuca serriola L., the mean reproductive parameters for the Q biotype were significantly greater than those for the B biotype (Muniz 2000). The Q biotype showed higher daily infestation rates than the B biotype on most tomato varieties tested (Nombela et al. 2001). On sweet pepper, the generation time for the Q biotype was found to be shorter than that of B biotype at 33 and 17 d, respectively. The number of cumulative generations of Q biotype also was somewhat greater than for the B biotype (Muniz & Nombela 2001). Furthermore, the resistance of the Q biotype to pesticides has been shown to be more resilient than observed for the B biotype (Anthony et al. 1995; Costa et al. 1993; Rauch & Nauen 2003). These collective results are likely linked to the increased pest status of the Q biotype in the Mediterranean region during the past several years.

Prior to this study, the Q biotype had not been reported in China. The high intra-population homogeneity suggests that a recent introduction of this biotype has occurred in China. Knowledge of insecticide resistant-Q haplotype populations in Spain (Ebert & Nauen 2000) and Israel (Nauen et al. 2002), and also that Spain and the Canary Islands are important producers of ornamentals crops that could have made their way to China in commercial trade, suggests a link between the movement of ornamentals species from the Mediterranean region and the recent presence of the Q type in China. Importation records have revealed that poinsettia and other ornamental plants were imported to China from Spain for the International Horticultural Exposition held in 1999 in Kunming, Yunnan Province. Such plants could have provided one possible route of entry into China for the Q biotype.

Herein, we report that the Q-biotype of B. tabaci was identified for the first time on infested ornamentals plants in several different regions of China. It is now important to closely monitor the potential establishment and spread of the Q biotype in the country to avoid its further dissemination, which could be devastating to vegetable and ornamental production. We have identified the Q biotype in distant locations in China, suggesting that multiple introductions may have occurred, or that plants from a single introduction were moved long distances from the original sources. Additional studies will be required to test this hypothesis and to determine if the Q biotype is sufficiently adapted to conditions in China to establish as an invasive pest and vector of plant viruses in ornamental, vegetable, and fiber crops.