APHlDIDiE OF SOUTHERN CALIFORNIA VIII 



Plant Lice Affecting the Citrus Trees* 



E. O. EssiG 



HORTICULTURAL COMMISSIONER OF VENTURA COUNTY 



Tliere has been much speculation in the minds of many of the citrus growers 

 and horticultural commissioners in Southern California regarding the plant lice 

 which affect the citrus trees. In fact, the ignorance regarding these insects, as 

 expressed by the secretary of the horticultural commissioner in a neighboring 

 county, certainly justifies tlie publication of a study such as this is intended to be. 

 At a recent meeting held in Los Angeles by the Los Angeles County Horticultural 

 Society, for the purpose of discussing the topic, "Insect Pests and Methods for 

 Their Control," it was emphatically argued b_y members of the Los Angeles Horti- 

 cultural Commission that the Black Peach Aphis, Aiphis niger Smith, was attacking 

 certain orange groves in Southern California. When it was said that the Black 

 Peach Aphis did not work on citrus trees there was such a confusion created in the 

 minds of all present that I do not wonder if many of the citrus growers, especially 

 in the districts where entire peach orchards are now being uprooted because of 

 that insect, are not afraid that the citrus trees may go next. Though this is an 

 extreme and remote possibility even under most ignorant direction, still it shows 

 how little is actually known regarding these aphids, which are designated by the 

 orchardists as small beetles, gnats, flies, etc., and it shows also liow great the 

 value of a thorough knowledge of them will be. 



Practically every locality in which citrus trees are grown, has been visited, 

 and extensive collections of plant lice made for the purpose of this study. Perliaps 

 some of these insects have been passed unobserved, but all the common injurious 

 forms are here presented, and comprise four genera and five species as follows : 

 Aphis cookii n. sp.. Aphis gosst/pii Glover, Macrosiphum citrifolii (Ashmead), 

 Green Peach Aphis, Myzus persicae (Sulz.), and the Citrus Aphid, Toxopteru 

 aurantiae Koch. All of these have been carefullj^ drawn and described from fresli 

 and living specimens so as to get accurate color notes and body shapes. 



In connection with the following descriptions I have also worked up, as 

 thoroughly as possible, all of the natural parasites and predaceous enemies which 

 prey upon the plant lice and which are responsible for their not doing greater 

 damage ; in fact, these practically control all infestations on citrus trees, with 

 the exception of sometimes a few localized cases during the early spring and 

 summer months. 



For the specific cases where tlie aphids are not controlled by natural enemies 

 and where it is necessary to employ artificial means of control I have prepared 

 spray formula", which are specially ada})ted for citrus trees, and which will usually 

 bring immediate relief if applied as directed. It is sometimes very imi)ortant to 

 have these at hand, particularlj' in cases of heavy infection of very young trees, 

 where considerable damage may be done in a very short time. 



*This masterly study of the Citrus Plant Lice, indicates again most clearly and indubit- 

 ably, the preeminent importance of having only men with some technical training, for the 

 important work in the office of County Horticultural Commissioner. It is not possible for 

 men without this training to work either intelligently, or with safety to the important 

 interests which they are supposed to guard. — EtI. 



