Phylloxera (
Daktulosphaira vitifoliae) is a tiny,
aphid-like
insect believed native to the eastern
United States which lives parasitically on grapevine leaves and roots. From a purely entomological perspective, phylloxera is interesting for having a fairly complex lifecycle. A single year will see multiple generations, some of which might live on leaves, some of which might live on roots, and only one of which will have wings and reproduce sexually.
Phylloxera is more well known for its historical effect on the viticultural industry, however. The insects form blister-like galls on leaves and roots which can result in defoliation and serious root damage, both potentially fatal to the vine. Native North American vitis labrusca grape vines, which coevolved with phylloxera, are fairly resistant to its damaging effects, but European vitis vinifera vines were not significantly exposed to phylloxera until the 19th century, when they proved extremely vulnerable to the pest. This became a major problem when in the late 1800s the transplantation of American rootstock spread phylloxera to vinifera vineyards around the world. The insect proceeded to decimate the European vines, creating a general viticultural crisis.
Grape growers theoretically could have responded by replacing vinifera plants with the resistant labrusca, but abandoning multi-thousand-year-old strains in favor of undomesticated labrusca, known for lending a strong, distinctive, and often disagreeable "foxy" taste to wine, was unthinkable. Attempts were made to solve the problem through crossbreeding, resulting in "French-American" hybrids, but eventually a more effective solution was found in the grafting of vinifera vines onto labrusca rootstock. This yielded phylloxera-resistant plants that retained traditional varietal characteristics, and most modern wine grapes are grown in this manner.
Phylloxera is now present in almost all grape-growing regions of the world, with some exceptions like Chile and parts of Australia where geographical isolation and quarantine have halted its advance. The one-two punch of phylloxera and Prohibition is widely credited with decimating the nascent American wine industry of the late 19th century, delaying the emergence of a mature native wine tradition until the 1970s.