THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 
25 
comparatively free from other infesting insects. Several experi- 
ments were conducted in that county in the summer of 1916 which 
bring out pretty well the varying effects of ant attendance on the 
mealybugs under different conditions. 
Experiment I. 
The subject of Experiment I was an orange tree whose 6 main 
branches had been cut back to stubs about 2 to 3 feet long. Three 
of the stubs, with 28 new shoots, were banded to exclude the ants, 
while the other 3, with 27 shoots, were left free to the ants. Mealy- 
bug infestation, prevalence of mealybug enemies, ant attendance, 
and vigor of tree were noted at intervals from the beginning of the 
experiment, April 14, to its conclusion, September 2, 1916. The re- 
sults are summarized in Tables III and IV. 
Table III. 
-Effect of the Argentine ant on abundance of mealybugs on orange. 
Los Angeles County, Cal., 1916. 
Date. 
Apr. 14 
May 3 
May 17 
July 6 
July 17 
Ants present. 
Mealybug infestation. 
74 clusters and groups 
106 groups 
361 groups of 10 to 150 bugs each 
112 groups, 10 to 50 ovipositing fe- 
males with egg masses 
As on July 6, but more young scat- 
tered over leaves 
Number 
of mealy- 
bug ene- 
mies seen 
28 
89 
19 
38 
301 
Ants excluded. 
Mealybug infestation. 
73 clusters and groups 
83 groups 
45 groups of 10 to 30 bugs each 
12 ovipositing females only with 
egg masses; 9 masses of destroyed 
mealybug material 
No living mealybugs 
Number 
of mealy- 
bug ene- 
mies seen. 
The larger groups or clusters of mealybugs at first occurred on 
the main branches, where they had passed the winter, but the mi- 
grating young formed smaller but populous groups at the bases of 
the smaller branches and of the leaves. It will be noted that at the 
outset of this experiment there was nearly complete uniformity in 
the amount of infestation between the branches from which ants 
w^re excluded and those to which ants had access. Substantial 
uniformity of infestation persisted up to May 3, when there was a 
somewhat greater number of groups of mealybugs and more scat- 
tered individuals on ant-invaded branches than on those kept free 
from ants. Between May 3 and July 17 the mealybugs rapidly 
diminished to complete disappearance on the branches from which 
ants were excluded, whereas on those to which ants had access mealy- 
bugs continued to increase rapidly for a time, reaching the high 
point of infestation on May 17. Thereafter the infestation de- 
creased on these branches also, but much more slowly than on those 
