Grape phylloxera

Description

Grape phylloxera, sometimes called simply phylloxera, is a native, very small, soft-bodied, aphid-like insect. It is most common in Europe and North America, but it is a serious economic pest wherever commercial grape vines are grown. In the United States, it occurs east of the Great Plains, where it coevolved with native grape species, and in the southwest, where it is a problem for commercial growers of table grapes and wine grapes.

Most adults are wingless females. They are oval in shape, less than 1 ⁄32″ long, less than 1 ⁄64″ wide, and yellowish-green, green, orangish-brown, or brown. As they age they become darker brown or purplish-brown. Reproductive females are pear-shaped. Nymphs are similar to adults but smaller.

Adults are difficult to identify because of their extremely small size. Grape phylloxera is usually identified by the galls it produces on the roots and leaves of grape plants. Galls on the tips of rootlets (nodosities) are yellowish-brown, hook-shaped swellings. Galls on larger roots (tuberosities) are rounded, wart-like swellings. Galls on the underside of leaves are small, green, rough, and more or less globular. They are not fuzzy.

Grape phylloxera originated in southeastern United States. Some American grape species, including wild grape (Vitis riparia), co-evolved with the pest and are resistant to it or tolerant to it. Others, including silverleaf grape (Vitis aestivalis var. bicolor), are more susceptible. Nodosities kill rootlets. Tuberosities weaken the roots and create decayed areas where other infections can invade, sometimes killing whole sections of root. Both result in reduced vigor of the growing plant. Once established, phylloxera cannot be eradicated.

It was introduced into France in 1860 when infected vines were imported for their resistance to powdery mildew. In the next 40 years the pest destroyed nearly two-thirds of wine grape (Vitis vinifera) vineyards in Europe.

Size

Less than 1 ⁄32″ long

Similar Species

Habitat

Ecology

Season

Up to 10 generations per year, late April to late October

Behavior

Life Cycle

Grape phylloxera has a complex life cycle with up to eighteen stages and four distinct forms: a wingless, root-feeding form (radicole); a winged, egg-laying form (alate); a wingless, sexual form; and a wingless, leaf-galling form (gallicole).

Radicoles are found on the roots year-round. They are the only nymph form that overwinters. They become active in the early spring and begin feeding on the roots as soon as the roots initiate growth. During the summer, fourth-instar larvae (crawlers) develop into mature females. These females reproduce asexually (parthenogenetically). They lay bundles of yellow, oval, female-producing eggs on the roots. Each female lays up to 400 eggs.

There are up to seven generations of crawlers per year. If there is a large infestation resulting in heavy competition for food, crawlers will disperse by crawling on the soil surface or climbing the plant and being blown by the wind. The last generation overwinters, most as hibernants, some as first or second-instar nymphs.

In the late summer some nymphs develop into winged alates that live only a few days. During this time they lay two to six eggs in bark on the trunk of a vine. Larger eggs are females, smaller ones are males. The eggs develop into wingless sexual form nymphs. These nymphs do not have mouth parts and do not feed. They molt four times, become sexually reproductive, and the female lays a single overwintering egg in a bark crack or crevice.

Nymph Hosts

silverleaf grape (Vitis aestivalis var. bicolor), hybrid grapes

wild grape (Vitis riparia) is resistant

Adult Food

Adults do not feed