8 BULLETIN 1040, U. S. DEPARTMENT OF AGRICULTURE. 



RELATION TO ARGENTINE ANT. 



In not a single instance has this mealybug become serious except- 

 ing where it has been attended by the Argentine ant {Irido?nyrmex 

 humilis Mayr). One case was noted in 1918 at Cucamonga where 

 the mealybug had been observed for several years previous to that 

 time, but never considered as doing any commercial damage. During 

 the year 1918-19 the area became infested with Argentine ants and 

 in the summer of 1919 control work on the mealybugs and ants 

 became imperative. In eA^er}^ known locality where this mealybug 

 now occurs it is attended by this particular ant. 



COMPREHENSIVE DEMONSTRATIONS OF CONTROL. 



EXPERIMENT NO. 1. DEMONSTRATION PLOT. 



The orchard selected for demonstration of control methods at 

 Upland in the summer of 1917 was near the center of the mealybug 

 infestation (fig. 5) and was considered one of the worst infested 

 groves, both as regards mealybugs and ants, in the colony. It con- 

 sisted of tw^o distinct plots of 10 acres each. The first 10 acres were 

 planted to Valencia (6 acres) and navel (4 acres) oranges and had 

 in all 674 trees. The second plot was planted largely to navel oranges 

 (8 acres), with approximately 2 acres of old lemons, making a total 

 of 676 trees. The trees were large and the lower limbs rested on the 

 ground. A careful inspection of the Valencia fruit in August, 1917. 

 showed an average of over 50 per cent of the fruit on each tree 

 infested, with from 20 to 35 mealybugs to a fruit, besides the infesta- 

 tions on the foliage and sucker growth. Many of the trees carried 

 from 90 to 100 per cent of infested fruit, with the foliage and new 

 growth as severely infested. Practically every tree had a trail of 

 ants and many were attended by two and even three trails. The 

 infestation on navel oranges and lemons in the second 10-acre plot 

 was as severe but showed only on the small green fruit and new 

 growth. 



Argentine Ant Eradication. 



Investigations, by the senior writer, of the common mealybug of 

 citrus trees resulted in the discovery that this insect was effectively 

 controlled by natural enemies, principally predators, in Argentine 

 ant-infested territory provided the ants were eliminated. Therefore. 

 Avhen a survey showed that the citrophilus mealybug occurred exclu- 

 sively in districts frequented by these ants, the first efforts were con- 

 fined to a campaign against the ant in the hope that only such activity 

 would be necessary, as had proved the case for the common mealybug. 



