72 BULLETIN" 647, TJ. S. DEPARTMENT OE AGRICULTURE. 



ness of natural enemies, especially certain internal parasites, partly 

 to overcrowding of the trees by armored scales and white flies, and 

 partly because of the poor physical condition of the trees. 



In Los Angeles County, Cal., where the trees are kept free from 

 other scales and vigorously growing, the mealybugs increase tre- 

 mendously as a result of ant attendance. Ordinarily they are kept 

 under complete control, where the ants do not occur, by their preda- 

 tory enemies. In orchards where fumigation has been neglected 

 and the trees become overcrowded with the black scale, the mealy- 

 bug does not benefit so much from ant attendance, and infestation is 

 much milder. 



The fluted scale has never been found in the orange groves proper 

 of Louisiana, and the part played by the Argentine ant in causing 

 the outbreak of this scale at Xew Orleans in 1916 is not known. The 

 occurrence of this outbreak, closely following the 1915 hurricane, 

 suggests the probability that the insect was largely spread by this 

 means. The fluted scale is unable, under present conditions, to thrive 

 on the orange trees of southern California even under the heaviest 

 ant attendance, apparently being held in check principally by the 

 Australian lady-beetle {Navius cardinalis Muls.), the green lace- 

 wings, and the dipterous larva CryptochoMum ?nonophleM Skuse. 



While the black scale occurs in New Orleans under constant at- 

 tendance by the Argentine ant, the ant has failed to bring it into 

 prominence there, and not a single infestation or even a single speci- 

 men has been discovered in any of the orange groves of Louisiana. 

 In California the black scale infestations often become very severe 

 after a single season during which fumigation has been neglected. 

 In two years' time the insect is capable of increasing from almost 

 none at all to such extreme numbers as to occupy every suitable 

 feeding spot on the trees which it infests. Attendance by the ant 

 for a single season does not noticeably increase the infestation of the 

 black scale in California, where it reaches a maximum whether the 

 ant is present or not. The natural enemies of this scale are not 

 numerous and effective enough to control it. 



"While exceptionally large numbers of the soft brown scale occur 

 on certain host plants or parts of such plants under ant attendance in 

 Louisiana, the natural enemies of this scale, especially the internal 

 parasites, continue to hold it to insignificant numbers in the orange 

 groves under present conditions. In Riverside County, Cal., this 

 scale appears to have increased considerably in certain ant-infested 

 orchards, but is generally controlled along with other scales by fumi- 

 gation. In Los Angeles County both the soft brown and the citri- 

 cola scales are scarce in ant-invaded as well as other orchards. The 

 soft brown scale, however, is undoubtedly more numerous on cam- 



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