Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Can molecules solve the bemisia conundrum when morphology cannot? A taxonomist’s perspective
California Department of Food and Agriculture, Sacramento, CA, USA. Correspondence: rgill@cdfa.ca.gov
Bemisia tabaci has a number of synonyms produced partly due to the extreme plasticity of the pupal stages. And even though the mechanisms for the pupal variability are now largely understood, as are the limits of this variability within some generic groupings, we still do not understand the relationships of the general morphology of whiteflies to species limits, or even to generic limits. Early work by Laurence Mound and Louise Russell showed that whitefly pupal morphology could be morphologically altered by environmental factors at least in the genera Bemisia and Trialeurodes. Further studies have shown variable pupal morphology to be common in many other genera, at least within the whitefly subfamily Aleurodinae. Current molecular studies are beginning to shed some light on a few morphological structures that could be reliable generic and specific characters for some of the Bemisia species and related genera, by giving us a glimpse of evolutionary relationships that have not been visible to the classical taxonomist previously. Hopefully this research will give us some indication of which morphological characters are useful in this way, and those characters, which are not of importance. While there are no good morphological characters for separating the various races of tabaci (as currently understood), there are some interesting differences in biology, mating behavior, cross fertility and virus transmission. Are there cryptic species involved? Some interesting molecular data is emerging that suggests strongly that there could be, considering the close morphological similarities of Bemisia formosana and graminus, and some of the Lipaleyrodes species studied so far. Recent molecular work has given us some insights into the relationships of many of the variants (biotypes=strains=races, genetic variants) of the Bemisia tabaci complex. Several of the species that are very close to tabaci morphologically include B. capitata; B. formosana and B. graminus and these are being included in a tabaci complex of species. But as an example of what we need to learn is the relationships of some other species in other genera that may in fact belong in the genus Bemisia and may even be part of the tabaci complex, such as Bemisiella, Lipaleyrodes, some species of Pealius (i.e. P. azaleae), and Parabemisia myricae. And a few of the races of those species appearing to be related to B. afer are also open for question. It will be of interest to see whether other genera such as Asterobemisia and Neobemisia are actually part of the B. afer complex, or are actually part of the same species. There are some schools of thought that the afer complex of species including tuberculata in South America, B. berbericola in North America, leakii and moringae from India and others may all be the same species that has been spread by humans, as has tabaci. One of the most important pupal characteristics that occur in Bemisia is the morphological shape of the vasiform orifice and lingula. The vasiform orifice is open at the posterior end, and the lingula usually protrudes beyond the operculum. However, a number of other genera share these characteristics to some degree. So far, only molecular data have been able to clarify certain generic positions within the Aleyrodinae, as it relates to these characters. Clearly, much additional work is needed to achieve a robust understanding of Bemisia.
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