INSECT PESTS AFFECTING THE CITRUS. 255 



and where the Vedalia do not appear, colonies of the Vedalia 

 should be i)rocured. 



In 18 , 2, the Aspidiolus aurantii, Maskell, was introduced, also 

 on trees from Australia. These were planted at Los Angeles, 

 and subsequently some were taken to Orange, from which 

 localities the pest spread. This species was described by Prof. 

 Maskell, and was imported into New Zealand from Sydney, 

 thus settling the question as to its source. Prior to 1880, little 

 or no damage was done by this pest. The greatest injury and 

 spread occurred between 1880 and 1890. While no effective 

 parasite that preys on this species has been found, the discovery 

 of the hydrocyanic acid gas treatment has proved a great boon 

 to the citrus industry, through which means the pest is kept 

 under control. 



In 1872 the Aspidiotus citrimts, Coquillett, was also intro- 

 duced, from Japan, into the San Gabriel Valley, on orange 

 trees. At first the insect made slow progress, and was not con- 

 sidered a very serious pest. Between the j^ears 1883 and 1889 

 it spread very rapidly, in fact alarmingly, throughout the val- 

 ley. In 1S89 a parasite of the genus Coccophagus was discov- 

 ered preying upon the scale, and it is now kept in subjection. 



Other species, the Mytilaspis citricola, Packard, and Mytilas- 

 pig Glovcrii, Packard, have been introduced on nursery trees, 

 principally from Florida, Ijut as yet they have been confined 

 to those trees in certain localities and have not spread. 

 Numerous other species are continually being discovered on 

 plants and trees imported from many parts of the world, and 

 promptly destroyed by Quarantine Officer Craw at San Fran- 



SPECIES IN CALIFORNIA. 



Genus ASPIDIOTUS, Bouche. 



This genus includes species of Diasjjwn-, in which the scale 

 of the female is circular or nearly so, with the exuvite at or 

 near the center, and the scale of the male somewhat elongated, 

 with the larval skin at one side of the center or near one 

 extremity. The last segment of the female usually presents 

 four groups of spinnerets; in a few species there are five 

 gronpS; and in some they are wanting. 



