INSECT PESTS AFFECTING THE CITRUS. 247 



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

 should be procured. 



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

 duced, presumably from Australia or Japan, into the San 

 Gabriel Valley on orange trees. At first the insect made slow 

 progress, and was not considered a very serious pest. Between 

 the years 1883 and 1889 it spread very rapidly, in fact alarm- 

 ingly, throughout the valley. In 1889 a parasite of the genus 

 Coccophagus was discovered preying upon the scale, and it is 

 now kept in subjection. 



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

 pis Gloverii, Packard, have been introduced on nursery trees, 

 principally from Florida, but 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 from many parts of the world. 



SPECIES IN CALIFORNIA. 

 Genus ASPIDIOTUS, Bouche. 



This genus includes species of Diaspinae, in which the scale 

 of the female is circular or nearly so, with the exuviae 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 

 groups, and in some they are wanting. 



