70 INJURIOUS AND BENEFICIAL INSECTS OF CALIFORNIA. 



and has probably been shipped into many parts of the State along 

 with the laurel trees. 



Food Plant. — The laurel (Laurus nobilis) is the only recorded host. 



Control. — Control measures are same as for the pear psylla. 



APHIDID^ (Family) 



PLANT LICE 



The members of this family comprise one of the most important 

 groups of destructive insects. Every one is familiar with the soft- 

 bodied winged and wingless plant lice which gather so abundantly 

 upon all sorts of plants. The beak or proboscis appears to rise in 

 the middle of the sternum, the legs are rather long and slender; the 

 wings when present, are membranous, with few veins and when 

 at rest are, except in a few cases, held roof-like over the abdomen. 

 Many of the females of this family have the power of producing 

 living young without sexual intercourse, and are usually called 

 viviparous or agamic females. True sexual forms usually appear 

 some time during the life-cycle. Winged or migratory forms also 

 occur. Some species live almost entirely underground while others 

 are aerial in habits. As this family plays such an important part in 

 the role of insect pests, we are including a large number of the most 

 common species. 



Control. — The treatment for insects which are both aerial and sub- 

 terranean in habits naturally calls for entirely different methods 

 for each. form. Of the plant lice two species stand out as splendid 

 examples of the subterranean form. They are the woolly apple aphis 

 and the black peach aphis, but both of these have aerial generations. 



METHODS FOR CONTROLLING UNDERGROUND FORMS 



Prevention. — In setting out a young orchard one of the first things to 

 consider is how to prevent the introduction of certain serious pests 

 and diseases which may be carried on nursery stock. Both the black 

 peach aphis and the woolly apple aphis are easily distributed on young 

 trees. The following precautions should be taken in setting out any 

 new peach, apple or pear orchard: 



1. Set out clean stock. Do not buy trees which have the roots 

 puddled unless the mud is washed off — it may hide the insects and 

 such infested trees would be severely handicapped and not worth 

 planting. 



2. The woolly apple aphis does very little damage to the Northern 

 Spy, especially is this true regarding the attacks on the roots, therefore, 

 if possible, buy apple trees grafted on Northern Spy roots, especially 

 if your section is troubled with this pest. 



3. Set trees fairly deep and keep the soil thoroughly cultivated 

 so as to get the roots down as far as possible. The woolly apple aphis 

 seldom works lower than ten inches below the surface. 



Sprays. — Before making applications around the crown of the tree 

 lor the control of root forms, first remove the earth around the roots 

 to a depth of six or seven inches and a distance of two or three feet 



