be required to
treat the pathological troubles of the grape fully; only such details
of the life histories of the several pests to be discussed as are
essential to a proper understanding of the control of the parasites
can be given here.

INSECT PESTS

Insects troubling the grapes are numerous, at least 200 having been
described in America, most of which have their habitat on the wild
prototypes of the cultivated vines of this continent. For this reason,
with a few exceptions, the insect pests of the grape in America are
widely distributed, abundant, and, therefore, often very destructive
to vineyards unless vigorously combated. The many pestiferous species
vary greatly in importance, depending on locality, weather and the
variety. Phylloxera, however, the country over, is most common and
deserves first attention.

_Phylloxera._

This minute sucking insect (_Phylloxera vastatrix_), injures the grape
by feeding on its roots. Decay usually follows its work on the roots
and is often more injurious than the harm done directly by the
parasite. This decay is always much more serious on European vines
than on those of our native species. The phylloxera is a native of the
United States east of the Rocky Mountains, from whence it was
introduced into France and from France into California, where it
causes much greater damage than elsewhere in the United States.
Wherever the pest is found, it is more injurious in heavy than in
sandy soils. In fact, in very sandy soils the vines are often
sufficiently resistant to be practically immune.

[Illustration: FIG. 36. Leaf-galls of the phylloxera.]

The life history of the phylloxera is very complex where the different
forms of the insect appear and need not be entered into in detail
here. East of the Rockies, the most evident indication of the presence
of the pest is great numbers of leaf-galls on the under side of the
leaves of the grape as shown in Fig. 36. These galls, however, are
seldom to be seen in California and are not present on Concords and
some other varieties in the East. The winter egg may be taken as the
beginning of the life cycle of the phylloxera. From a single winter
egg a colony may arise, the first insect after hatching making its
way to the leaves where it becomes a gall-maker and gives rise to a
new generation of egg-laying root-feeders. On varieties and in regions
where the gall form is not found, the insect probably goes directly
from the winter egg t