200 



APPLIED ENTOMOLOGY 



tributed. The adult is a small insect more or less completely covered by- 

 white, cottony or woolly threads of wax which practically conceal the 

 louse beneath. Recent studies have shown that in most cases at least, 

 the winter is spent in the egg stage in crevices in the bark of the elm. 

 The eggs hatch in spring and the young lice pass to the buds and attack 

 the leaves when these develop, causing them to become deformed, curled 

 and clustered together forming "rosettes." Several generations partici- 

 pate in this work. 



During the later spring months winged migrants are produced and 

 these pass to the apple, hawthorn and a few other related trees where 



they locate on the under side of the leaves 

 and produce young which crawl to thin 

 places, wounds or water shoots and there 

 locate and reproduce during the summer and 

 fall (Fig. 192) until cold weather comes on, 

 when migrating forms are produced which 

 return to the elm where the eggs are laid. 



This life history is complicated by the 

 fact that during the summer some of the 

 plant lice migrate from the branches of the 

 apple tree to its roots and feed there, pro- 

 ducing knots and swellings which interfere 

 with the nutrition of the plant, and if suffi- 

 ciently abundant may cause its death. These 

 lice are believed to remain on the roots the 

 year around, generation after generation, but 

 with their ranks recruited from time to time 

 by migrants from the aerial members. Some 

 of the latter also, are believed to remain on 

 the apple all winter as hibernating nymphs. 



The amount of injury to the apple caused 

 by this insect above ground is not very great 

 except perhaps on nursery trees. Woolly spots 

 at scars and wounds on the branches, notice- 

 able chiefly in the fall, are not abundant enough to affect the trees 

 much, usually. The root form, however, is sometimes quite injurious, 

 particularly south of the latitude of Washington, and young orchards 

 may suffer severely. 



Control. — The waxy "woolly" threads covering the bodies of these 

 insects make control more difficult by spraying than would otherwise 

 be the case, as the threads repel the spray. Nicotine sulfate 40 per cent, 

 standard formula, or kerosene emulsion 1 part to 9 of water, driven with 

 much force are about the only treatments for the aerial forms which have 

 given much success. It is evident that elms growing near apple trees 



Fig. 192. — Apple twig show- 

 ing Woolly Apple Aphis 

 {Eriosoma lanigera Hausm.) 

 and swellings of the twig pro- 

 duced by their attacks. About 

 twice natural size. {Original.) 



