8 BULLETIN 1040. U. S. DEPARTMENT OE AGKICULTUKE. 
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 (iridomyrmex 
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 every 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 two distinct plots of 10 acres each. The first 10 acres were 
planted to Valencia (6 acres) and navel (± acres) oranges and had 
in all 074 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, 
when 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. 
