INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 87 



ter lay the over-wintering eggs. Except that some of the viviparous 

 females pass the winter on grasses, and the fact that they migrate 

 from the trees to the grasses in late spring thus vacating the trees 

 during the summer months, the life history of this aphis greatly 

 resembles that of the green apple aphis. 



Nature of Work. — The aphis works upon the stems and leaves of 

 grains and grasses, often doing very serious damage. In Imperial 

 County the barley crop is sometimes practically destroyed in certain 

 fields by a plant louse supposed to be this species. The leaves of 

 fruit trees are curled similar to the work of the green apple aphis. 



Distribution. — The oat aphis is generally distributed throughout 

 the State. 



Food Plants.— Apple, barley, blue-grass (Kentucky and Canada), 

 brome grass, burdock, cat-tail, celery, cheat, upright chess, choke- 

 cherry, wild black cherry, corn, broom corn, crab-grass, dogwood, 

 fescue grass, hawthorn, Johnson grass, Koeler's grass, meadow grass, 

 melic grass, oat, oat-grass, orchard grass, pear, plum, quince, rescue 

 grass, redtop grass, reed canary grass, rye, Italian rye grass, wild 

 rye (Ely mil s canadensatus and other species), shepherd's purse, sor- 

 ghum, tickseed, timothy and wheat are among the recorded food 

 plants of the oat aphis. 



Natural Enemies. — An internal parasite (ApJiidius testaceipes Cr.), 

 the larvae of the American syrphid fly (Syrphus americanus Wied.) 

 and various ladybird beetles prey extensively upon this aphis in 

 California. 



Control. — Because of the extensive attacks of this aphis in grain 

 fields, the ordinary methods of control are not always practical. 

 Spraying as recommended at the beginning of the chapter may be 

 used on fruit and other trees and to some extent in the grain fields. 

 In the case of the latter, however, crop rotation and especially clean 

 culture during the winter will aid greatly in reducing the spring 

 and summer broods by destroying the hibernating lice. In the locali- 

 ties where the grain is allowed to grow through the winter affording 

 ideal feeding places for the over-wintering viviparous females, the 

 aphis is worst, making control practically impossible. 



THE CLOVER-APPLE APHIS 



Aphis baJceri Cowen 



Description.— The stem-mothers are pink or deep red with green 

 markings on the dorsum arranged in a mottled effect. The honey- 

 tubes are short and pale yellow. The size is medium, the length 

 averaging about 1-12 inch. This form is usually found upon fruit 

 trees early in the spring. The later generations are yellowish-green 

 with an orange-colored spot at the base of each cornicle. The color 

 of specimens feeding on clover varies from yellowish-green to pink. 

 The winged forms are yellowish-green with the antenna?, head and 

 thorax black. There is also a conspicuous shining black patch on 

 the dorsum of the abdomen. The legs, honey-tubes and tail or cauda 



