56 MISC. PUBLICATION 273, U.S. DEPT. OF AGRICULTURE 



APHIDS 



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 (47). 



The aphids exude quantities of honeydew, which drips over the 

 leaves and onto the ground beneath. This is a favorite food of 

 ants, which 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 feed- 

 ing ; and forest trees are sometimes so weakened that after a sea- 

 son 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 range from one 

 to several in a single season, with more or less overlapping. 



On shade and ornamental trees the aphids can be controlled by 

 spraying, when they are first observed, with 4 or 5 pounds of fish- 

 oil soap in 20 gallons of water, or with 1 2 pint of nicotine sulfate 

 in 50 gallons of water to which 2 pounds of soap has been added. 

 Crude-oil emulsion and commercial lime-sulfur are used as dor- 

 mant sprays to kill the eggs. They are applied in the spring, about 

 the time the buds begin to swell. 



The spruce aphid (Neomyzaphis abietina (Wlkr.)) is by far the 

 most destructive member of this group of sap-sucking insects that 

 attack forest trees in the West. It has killed millions of board 

 feet of Sitka spruce along the tidelands of the Oregon and Wash- 

 ington coast (fig. 22) and the Columbia River, and has caused 

 considerable damage to this conifer on the better inland sites. The 

 wingless aphids occur early in the summer on the old needles. 

 These insects are dull green and range in size from very minute 

 when young to about 3 16 inch in length when full grown. Appar- 

 ently this insect has an alternate host, as it disappears from the 

 Sitka spruce in midsummer only to reappear again the next 

 spring. On shade and ornamental trees the pest can be controlled 

 by spraying with such contact insecticides as nicotine sulfate, 

 miscible oil, or lime-sulfur. 



The Monterey pine aphid (Essigella californica Essig) is a 

 small, light-green, pear-shaped insect about y 8 inch in length and 

 with very long hind legs. It is reported as feeding on the needles 

 of Monterey and ponderosa pines and Douglas-fir in California and 

 Oregon. Schizolachniis yiniradiatae Davidson is a dark-green 

 aphid, much smaller than the last named, and is covered with a 

 cottony wax. This species attacks the needles of Monterey and 

 other pines in central California. S. tomentosus DeG. is a yellow 



