38 BULLETIN 647, U. S. DEPARTMENT OF AGRICULTURE. 



INFLUENCE OF THE ANT ON ABUNDANCE OF THE SOFT BROWN SCALE IN CALIFORNIA. 



There was no opportunity during the season of 1916 to study the 

 effect of the ants on abundance of the soft brown scale in the orange 

 groves of southern California because of the scarcity of the scales. 

 Larger groups of this scale occur on various ornamentals where 

 attended by the ants than where there are no ants, and its abundance 

 on camphor, bottle, and pepper trees and many others along some 

 of the streets of Pasadena where the Argentine ant occurs makes it 

 appear that the ant has the effect of greatly increasing the infesta- 

 tions there. Xeither the soft brown scale nor the closely related 

 citricola scale 1 occurred in any greater number in the ant-invaded 

 orange groves of Los Angeles County than in those where the ant 

 did not occur. In Riverside County, on the contrary, large groups 

 of the soft brown scale were found more easily in the ant-invaded 

 than in the noninvaded orchards. Quayle 2 has noted that the soft 

 brown scale becomes especially serious under the influence of the ant 

 in that county. Several orchards were mentioned by Mr. D. D. 

 Sharp, Riverside County horticultural commissioner, in which the 

 soft brown scale had become so numerous as a result of attendance 

 by the ant as to attract general attention. In one of the most severely 

 ant-infested orchards, however, which it was said had not been fumi- 

 gated for several years, there was a large parasitization of the soft 

 brown scale, as high as 82 per cent of them being found destroyed 

 by parasites in a group under heavy ant attendance. 



It appears, therefore, that the Argentine ant may afford enough 

 protection to the soft brown scale at times on certain trees or in cer- 

 tain localities to cause the formation of larger groups than is cus- 

 tomary and retard the destruction of the insect by its natural ene- 

 mies. This effect has not, however, been marked enough either in 

 California or Louisiana to change the rank of the scale as a citrus 

 pest of merely minor importance. This is due to the fact that in- 

 ternal parasites and not predacious enemies are the chief factor in 

 the natural control of the scale. 



RELATIONS WITH THE CITRUS WHITE FLY.» 



The Ant as an Enemy of the White Fly. 



The only direct relation which the Argentine ant bears to the 

 citrus white fly is that of predator. The first knowledge of this fact 

 came as a result of observations made in an orange grove at Happy 

 Jack, La., in April, 1913. At that time the prevailing belief, which 



1 Coccus citricola Campbell. 



2 Quayle, H. J. In Jour. Econ. Ent, v. 9, p. 472. 1916. 



3 The citrus white fly (Dialeurodes citri Ashm.). The cloudy-winged white fly (Dialeu- 

 rodes citrifoUi Morgan) also occurs in Louisiana, but is greatly outnumbered by the 

 first-named species. 



