INJURIOUS AND BENEFICIAL INSECTS OP CALIFORNIA. 



63 



leaves, especially of apple and alfalfa. There are from three to four 

 broods a year. The adults hibernate in sheltered places, under leaves, 

 in the grass and weeds. 



Nature of Work.— During the summer and fall months the leaf- 

 hoppers often become exceedingly abundant, and do much damage by 

 attacking the new growth at the tips of the branches, causing the leaves 

 to turn yellow and curl, and thereby stunting and producing under- 

 sized trees. Young nursery trees suffer most. On older trees they work 

 usually upon the undersides of the leaves. 



Distribution. — This leaf -hopper is apparently limited in its distri- 

 bution in the State. 



Food Plants. — Though the apple leaf -hopper is primarily a nursery 

 pest, affecting especially apple trees, a large number of plants are 

 attacked, including alfalfa, bean, birch, blackberry, box-elder, buckeye, 

 buckthorn, buckwheat, ca- 

 naigre, celery, cherry, choke- 

 cherry, clover, corn, cotton- 

 wood, currant, dahlia, elm, 

 gooseberry, grape, grass, 

 hazelnut, hemp, hollyhock, 

 jimpson weed, linden, maple, 

 oak, oat, pear, plum, potato, 

 raspberry, rhubarb, rose, 

 snowball, sugar beet, sumach, 

 syringa and black walnut. 



Control. — The most effec- 

 tive time to control the apple 

 leaf-hopper is when it is in 

 the nymphal stage, in the 

 spring and summer months. 

 Kerosene emulsion and to- 

 bacco decoction ("black leaf 

 40," 1 pint to 100 gallons of 

 water) give good results if 

 applied before the leaves 

 become curled and afford 

 protection for the hoppers. 

 Nursery trees may be readily 

 cleaned by bending the twigs 

 and dipping the infested tips 

 in a bucket containing one 

 of the above solutions. June and July are the best months for treat- 

 ment. Sticky shields and hopper-dozers are also valuable in capturing 

 the hoppers in nurseries. Clean culture should be practiced in the 

 orchards and nurseries to eliminate as far as possible all weeds and 

 grasses which serve as food plants. 



Natural Enemies. — The most effective natural enemy here is the 

 small dark bug (Triphleps tristicolor White), which preys upon the 

 nymphs by puncturing their bodies and extracting the contents. 



The larvae of the green lacewings also prey upon the young hoppers. 



Fig. 52. — The rose leaf-hopper, Empoa rosce 

 (Linn.). Adults on an apple leaf, which shows 

 their characteristic work. (Original) 



