THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 



27 



From May 17 to July 17 the mealybug enemies rapidly decreased 

 and disappeared from branches kept free from ants and greatly in- 

 creased on those where ants were present, following, as would 

 naturally be anticipated, the available food supply. In the succeed- 

 ing period of the experiment, from July 17 to September 2, after a 

 certain amount of fluctuation, depending upon the supply of host 

 insects, the natural enemies finally disappeared from all branches 

 with the practical disappearance of their prey. 



Experiment II. 



The second experiment was conducted in the same locality, at 

 Alhambra, Cal., on eight bearing navel-orange trees, four of which 

 were banded with adhesives on April 24 and kept free from ants, 

 while the alternating four were left accessible to ants for compari- 

 son. The results of this experiment, which are summarized in Table 

 V, were similar to those in the preceding experiment, except that 

 on the ant-invaded trees heavy mealybug infestation persisted 

 throughout the experiment, or until September 12. 



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

 trees, Los Angeles County, Cal., 1916. 





Ants present. 



Ants excluded. 





Mealybug infestation. 



Mealybug infestation. 



Date. 



On fruits. 



On other parts of 

 trees. 



On fruits. 







Total 

 number 

 exam- 

 ined. 



Num- 

 ber in- 

 fested. 



Per 

 cent in- 

 fested. 



Total 

 num- 

 ber ex- 

 amined. 



Num- 

 ber in- 

 fested. 



Per 

 cent in- 

 fested. 



On other parts of 

 trees. 



May 24 

 July 10 

 July 24 



Aug. 7 



Aug. 31 

 Sept. 12 



800 

 1,405 

 1,261 



1,596 



1,310 

 1,249 



1200 



328 

 766 



923 



728 

 421 



25 



24 

 60.7 



57.8 



55.5 

 33.7 



Approximately as on 



Apr. 24. 

 242 groups of 1 to 5 



mealybugs. 

 296 small groups, 



many scattered 



young. 

 206 small groups, 



many scattered 



young. 



Many scattered 



do 



800 

 1,154 

 1,263 



1,288 



1,086 

 1,282 



U50 

 5 

 34 



91 



59 



64 



18.7 



.43 



2.6 



7. 



5.4 

 4.9 



Approximately as 

 on Apr. 24. 



12 groups of 1 to 5 

 mealybugs. 



7 small groups, 

 many scattered 

 young. 



Many scattered in- 

 dividuals. 



None. 

 Do. 









i From 1 to 5 mealybugs hidden under the sepals only of each infested fruit. 



At the beginning of this experiment, April 24, mealybug infesta- 

 tion was slight, only 103 scattered individual mealybugs and small 

 groups occurring on the trees from which ants were excluded and 70 

 individuals and small groups on those to which ants were allowed 

 access, the ant-excluded trees being slightly more infested. 



On May 24 young mealybugs were found concealed under the 

 sepals of 25 per cent of the young fruits on the ant-invaded trees 



