46 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



oratory experimenters, working with 

 species having both winged and wingless 

 agamic females, have succeeded in caus- 

 ing the aphids to produce winged forms 

 or only wingless forms at will by sub- 

 jecting the insects to certain tempera- 

 tures and by introducing certain chemi- 

 cals into the food-plants. 



Plant-lice increase very rapidly, some 

 species producing 20 or more generations 

 in a single year, each female on arriving 

 at maturity producing in course of time 

 from 10 to 400 eggs or young, as the case 

 may be, and varying with the species. 

 Their numbers are kept in check by a 

 large number of natural enemies. These 

 include parasitic wasps of the families 

 Braconidae and Chalcididae. and preda- 

 ceous forms such as lady-bird beetles 

 (Coccinellidae). Syrphus-fly maggots (Syr- 

 phidae), spiders, larvae of lace-wing flies 

 fChrysonidae) and aphis-lions (Hemer- 

 obidae), and certain predaceous Heterop- 

 tera. Ants attend aphids to feed on the 

 sweet substance excreted by them, and 

 in certain forms play the role of hus- 

 bandmen towards them, carrying them 

 off and caring for them during the win- 

 ter months. 



Biblioerapliy 



A complete bibliography of economic 

 plant-lice would occupy too much space 

 for the purpose of this paper. The fol- 

 lowing references include literature deal- 

 ing with practically all injurious species: 



"Insect Pests of Farm, Garden and Or- 

 chard"; E, D. Sanderson (.John Wiley & 

 Sons); 1912. 



"The Aphides Affecting the Apple": 

 A. L. Quaintance (U. S. Dept. Agric. Circ. 

 No. 81); 1907. 



"The Melon Aphis": F. H. Chittenden 

 (U. S. Dept. Agric. Circ. No. 80); 1906. 



"The Woolly Aphis of the Apple"; C. L. 

 Marlatt (U. S. Dept. Agric. Circ. No. 20) ; 

 1908. 



"The Pea Aphis": F. H. Chittenden (U. 

 S. Dept. Agric. Circ. No. 43); 1909. 



"Two Plant-Lice of the Peach": C. P. 

 Gillette and G. P. Weldon (Colo. Agric. 

 Exp. Station, Bull. 169); 1910. 



"A Few Orchard Plant Lice"; C. P. 

 Gillette and E. P. Taylor (Colo. Agric. 

 Exp. Station, Bull. 133); 1908. 



"The Potato Plant Louse"; E. M. Patch 

 (Maine Agric. Exp. Station, Bull. No. 

 147); 1907. 



"The Corn-Leaf Aphis and Corn-Root 

 Aphis"; F. M. Webster (U. S. Dept. Agric. 

 Circ. No. 86) ; 1907. 



"The Spring-Grain Aphis"; E. M. Web- 

 ster (U. S. Dept. Agric. Circ. No. 85): 

 1907. 



APPLE 



Tlie Green .Vpple .\pliis 



Aphis pomi De Geer 



This is the green aphis that is often 

 very abundant on the leaves, young 

 shoots and young fruit of apple and pear. 

 It also infests quince, pomegranate and 

 occasionally plum and hawthorn. Its life 

 history is as follows: A week or so be- 

 fore the buds open in the spring the 

 young dark green stem-mothers com- 

 mence hatching from the winter eggs and 

 for a time feed on tender bark or on the 

 bud scales. After the buds open they 

 confine their attentions to the foliage. 

 In about 25 days the lice are full grown, 

 pale green with a dark head, cornicles 

 and tail. The stem-mother lice are always 

 wingless. Upon attaining maturity they 

 at once begin depositing young, produc- 

 ing within three weeks from 25 to 100 

 young. A few of the lice of the second 



Fis. 1. Wingless Female of Green Apple .\phis. 

 Stem Mother — Greatly enlarsed. 



— Author's Illustration. 



