A century and a half ago an alien insect alighted in Europe.
It displaced millions, ruined local economies and forced scientists, politicians and ordinary folk into a frenzy of defensive activity.
Phylloxera, a member of the group known to entomologists as Hemiptera, or "true" bugs
(as opposed to all the other critters known colloquially as bugs),
appeared in France in the 1860s and proceeded to eat its way through many of the Old World's vines.
It then spread to pastures new. It was first recorded in Australia in 1875 and in South Africa in 1886,
threatening similar devastation to the vineyards of those European colonies.
Eventually, French and American scientists found a solution by grafting European vines onto the imported roots of American ones.
Now, a more recent group of French and American researchers report in BMC Biology that they have sequenced phylloxera's genome,
and that hidden within this lie clues to the insect's origins and spread.
Nineteenth-century agronomists rapidly divined that phylloxera had come from North America.
That fact provided the rationale behind their graft-based answer to the problem—which is still all that stands between cultivated vines and the bug.
This is that having co-evolved with the insect, American vines had developed resistance to it.
But where exactly it came from on that continent, nobody knew.
One theory held British gardeners responsible because they had brought wild American vines to Europe for decorative purposes.
From Britain, this theory went, phylloxera reached the European mainland via the south of France, the first place where it devastated vineyards.
That, though, turns out to be a calumny against les Anglais.
By comparing the genetic sequence of European phylloxera with those of populations from wild vines in the United States,
Claude Rispe and Fabrice Legeai of the French National Research Institute for Agriculture, Food and the Environment (INRAE)
来自法国国家农业、食品和环境研究所（INRAE）的Claude Rispe和Fabrice Legeai
and their colleagues have narrowed the search to the once-French territory of the Mississippi Valley
(the upper Mississippi, to be precise—though one of the paper's authors,
Paul Nabity of the University of California, Riverside, plans to keep following the river south, sampling phylloxera as he goes, so the matter is not closed).
The evidence is that there is a striking similarity between the European sequence
and that of two phylloxera populations on a wild vine called Vitis riparia in Wisconsin and Illinois.
This is enough, Dr Nabity says, to indicate that V. riparia was the bug's original host and the upper Midwest its source.