There is another group of weevils, nearly related to the common plum
curculio, the species of which attack immature nuts. In this group the
snout is much shorter than in the group just described, and the insects
are considerably smaller. There is one species, _Conotrachelus
juglandis_, that confines its attacks to the young fruits and shoots of
walnuts of the butternut group, another, _Conotrachelus retentus_, that
seems to attack exclusively the black walnut fruits from the time they
set until they are half grown, still another, _Conotrachelus affinis_,
that appears to attack only half-grown hickory nuts. Another species,
_Conotrachelus aratus_, feeds abundantly in some localities within the
leaf petioles of hickory. At least two other species of the group
commonly attack acorns. Those injuring walnuts lay their eggs on the
concave side of crescent-shaped punctures which they eat in the husks of
the young nuts. The larvae developing from the eggs cause the nuts to
drop within a few weeks and the larvae enter the ground to complete
their transformation. There is a divided tendency with some of these
species to attack the young wood and leaf stems of the introduced
species of walnut. Dr. Morris states that he has had young Japanese
walnut trees killed by _C. juglandis_ feeding in the grub stage within
the branches. He has, however, found that the pest succumbs to an
arsenate of lead spray.

Species of this group are apt to have alternating periods of increase
and decrease and a year of great abundance may be followed by a year of
comparative scarcity. This variation is due, at least in part, to the
fact that the larvae, as they feed within the tissues of their host
plants, often become rather heavily parasitized by certain two-winged
and four-winged flies, the parasitized larvae dying before they reach
the adult stage. Nature in this way does considerable toward holding the
pests in check, but artificial means of control will often need to be
considered.

The third group referred to is represented by a two-winged fly, about
the size of the common house fly, known technically as _Rhagoletis
suavis_, and commonly as the walnut husk-maggot. The fly is light brown
in color, with broad, irregular, dark brown bands on the wings. It
appears when walnuts are nearly grown and deposits clusters of small,
white eggs within punctures in the husks. Maggots hatch from the eggs
and at the time the walnuts drop these maggots are ofte