INSECT ENEMIES OF WESTERN FORESTS 45 
B. Trees appearing in fairly good health but leaves or stems badly 
stunted, galled, or swollen; sometimes with queer protuber- 
CFI CES ae a a al . ae gall makers, page 52. 
1. Cone-shaped galls on terminal twigs of spruce 
spruce gall bark lice, page 47. 
2. Swollen twigs of white pine, covered with white incrusta- 
HONSSe Eo ae ee BESS Sane Pres er woolly pine louse, page 48. 
3. Galls at base of pine needles causing premature  shed- 
(ONG Sega Sass tee ee ee ace econ Pe a ee pine needle mite, page 52. 
APHIDS OR PLANT LICE 
Aphids are small, delicate, soft-bodied insects with pear-shaped or 
globular bodies and long legs. They range from almost colorless 
translucent to greenish or almost black. As a rule they are without 
protective covering and often occur in dense colonies on leaves or 
tender terminals of trees, where they feed by sucking the juices. 
The aphids exude quantities of honeydew, which drips over the 
leaves and onto the ground beneath. This is a favorite food of 
ants, who cultivate and tend the aphids for it, and for this reason 
the aphids are often referred to as “ant cows.” ‘The honeydew also 
becomes a fertile medium for the growth of a black smut that covers 
the leaves, causing the trees to appear as if they had been sprayed 
with crude oil. Shade and ornamental trees are rendered particularly 
unsightly, besides being weakened by the aphid feeding; and forest 
trees are sometimes so weakened that after a season or two they 
die from the injury. 
Aphids are remarkable because of their peculiar manner of de- 
velopment and the difference in the mode of reproduction of sepa- 
rate generations of the same species. They reproduce both sexually 
and also without mating, and both winged and wingless forms 
occur. The number of generations of aphids may vary from one or 
two to several in a single season, with more or less overlapping. 
On shade and ornamental trees the aphids can be controlled by 
spraying the insects, when they are first observed, with a mixture 
of 4 or 5 pounds of fish-oil soap in 20 gallons of water, or with one- 
half pint of nicotine sulphate in 50 gallons of water in which 2 
pounds of soap has been dissolved. Crude-oil emulsion and com- 
mercial lime-sulphur solutions are used as dormant sprays to kill 
the eggs. They are applied in the spring, about the time the buds 
begin to swell. | 
The spruce aphid (Aphis abietina Walk.) is by far the most 
destructive member of this group of sap-sucking insects that attack 
forest trees in the West. In recent years it has killed millions of 
feet of Sitka spruce along the tidelands of the Oregon and Wash- 
ington coast (fig. 20) and the Columbia River, as well as having 
caused considerable damage to this conifer on the better inland sites. 
The wingless aphids occur early in the summer on the needles and 
tender growth of Sitka spruce. These insects are dull green and 
range in size from very minute young insects to full-grown winged 
aphids about three-sixteenths of an inch in length. Apparently this 
insect has an alternate host, disappearing from the Sitka spruce in 
midsummer, only to reappear again the next spring. No practical 
remedy has been suggested under forest conditions, but on shade 
and ornamental trees the pest can be controlled by spraying with 
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