|Bemisia tabaci or maybe not|
The silverleaf whitefly (Bemisia tabaci, which is also referred to as Silverleaf whitefly strain B) is one of several whiteflies that are currently important agricultural pests.Their nymphs use parts of their mouth to stab into the plant and consume the plant’s juices. The honeydew they leave behind can induce the growth of sooty molds, which can then reduce the plants ability to absorb light. This results in less growth, lower yield, and poor quality plants.It is thought that the United States alone has suffered crop and ornamental plant damages in excess of $1 billion through this pest.
For 100 years, outbreaks were sporadic and relatively small, but this changed in the mid-1980s with widespread outbreaks occurring across the south western USA. This was odd because the whitefly was well known across the region as a minor pest yet here it was destroying large amounts of crops. Although there were no morphological differences, molecular and biological data indicated that the outbreak pest was a different species. Using this information, it was proposed that rather than one species, Bemisia tabaci was composed of at least 28 different morphologically indistinguishable species, all separated by at least 3.5% divergence in their DNA Barcode. To date 34 species have been delimited using the same metrics.
These findings are supported by mating compatibility studies. These have shown that crosses between individuals identified as different cryptic species are reproductively isolated to the point that in most cases copulation does not occur and where it does, the resulting progeny are either sterile or reproductively inferior to their parents.
There was only one question left: Who is the the real Bemisia tabaci originally described in 1889?
A group of researchers has now solved this mystery. They were able to sequence a 496 bp DNA Barcode fragment belonging to a single whitefly taken from the original 1889 collection by Panayiotis Gennadius who first described the species. He had travelled to Greece to identify a small fly-like pest that was devastating tobacco crops there. It is clear now that it wasn't this species that invaded the US but rather a species that was provisionally called "Mediterranean". This species has now begun its own global journey of invasion spreading from its Mediterranean home range to at least 10 different countries in Europe.