THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 



29 



after the mealybugs had become located, the ants were excluded 

 from 3 of the plants on which there were 4,573 young bugs and 

 allowed free access to the remaining 3, on which there were 3,094 

 mealybugs. On August 21 there were only 577 mealybugs left on 

 the plants from which ants were excluded, 40.6 per cent of the 

 leaves being infested with an average of 3.2 mealybugs each ; whereas 

 on the plants traversed by ants there were 5,461 mealybugs, 74.5 

 per cent of the leaves being infested with an average of 29 mealy- 

 bugs each. 



Experiment V. 



In the fifth experiment, which was conducted at Duarte, Cal., it 

 was demonstrated that the effect of the ants in increasing the abund- 

 ance of mealybugs may be largely neutralized in the presence of un- 

 checked infestation by the black scale {Saissetia oleae Bern.). Ten 

 bearing naval-orange trees of about equal condition and equal 

 mealybug, ant, and black-scale infestation, the last-named being 

 heavy, and with fully 90 per cent of sooting of the leaves, the trees 

 not having been fumigated since 1913, were selected for this experi- 

 ment. On April 20 five of the trees were banded with adhesive mix- 

 ture to exclude ants, and the alternating five left accessible to ants 

 for comparison. The results of this experiment are summarized in 

 Table VI. 



Table VI. — Effect of the Argentine ant on abundance of mealybugs on orange 

 trees heavily infested with the black scale (Saissetia oleae). Los Angeles 

 County, Cal., 1916. 





Ants present. 



Ants excluded. 





Mealybug infestation. 



Mealybug infestation. 



Date. 



On fruits. 



On other parts of 



On fruits. 







Total 



number 







Total 



num- 

 ber ex- 

 amined. 







On other parts of 





Num- 

 ber in- 



Per 

 cent in- 



trees. 



Num- 

 ber in- 



Per 



cent in- 



trees. 





ined. 



fested. 



fested. 





fested. 



fested. 











Per ct. 









Per ct. 





May 25 



100 



80 



80 



Many scattered 

 mealybugs and 

 small groups. 



100 



94 



94 



Many scattered 

 mealybugs and 

 small groups. 



July 7 



437 



156 



35.6 



11.4 per cent of new 

 shoots infested. 



304 



165 



54.2 



33.1 per cent of new 

 shoots infested. 



July 21 



455 



154 



33.8 



51 groups of 1 to 30 

 young and 17 adults 

 with egg masses. 



382 



193 



50.5 



36 groups of 1 to 15 

 young and 47 

 adults with egg 

 masses. 



Aug. 15 



409 



143 



34.9 



81 groups of 1 to 5 

 mealybugs each. 



376 



165 



43.8 



20 groups of 1 to 5 

 mealybugs each 



Sept 11 



364 



198 



54.5 



79 groups of 1 to 5 

 mealybugs each. 



340 



137 



40.2 



41 individual 

 mealybugs only. 



