A pest’s genome reveals its past

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...