THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 
.Experiment VI. 
31 
In the following experiment, verifying the results of the one pre- 
ceding, 4 trees longer subject to unchecked black-scale infestation 
were used, 2 of them being banded on June 2, the other 2 left free 
to ants. 
Table VII. — Effect of Argentine ant on abundance o fmealybugs in the presence 
of heavy black-scale infestation on orange. Los Angeles County, Gal., 1916. 
Ants present. 
Ants excluded. 
Date. 
Fruit infestation. 
Fruit infestation. 
With 
mealy- 
bugs. 
With 
black 
scale. 
With 
sooty 
mold. 
With 
mealy- 
bugs. 
With 
black 
scale. 
With 
sooty 
mold. 
Per cent. 
37.5 
32.9 
48.1 
39.6 
Per cent. 
Per cent. 
Per cent. 
32.5 
20.2 
20.5 
21.2 
Per cent. 
Per cent. 
July 7 
94.4 
53.5 
91.7 
100 
100 
100 
100 
45.7 
98.7 
100 
Aug. 15 
100 
Sept. 11 
100 
The fruit infestation on different dates, summarized in Table VII, 
shows that mealybugs were always somewhat more numerous on the 
fruit patrolled by ants, but that almost no change in degree of in- 
festation occurred on either lot of trees. Most of the fruit on all 
trees was infested with young black scales, and all was sooty through- 
out the experiment. 
RELATION OF THE ANT TO MEALYBUG OUTBREAKS IN SOUTHERN CALIFORNIA. 
The foregoing experiments establish beyond a doubt that the at- 
tendance of ants upon mealybugs in Los Angeles County, Cal., has 
the effect of greatly increasing their abundance, particularly during 
the first half of the summer, upon healthy trees comparatively free 
from other scale insects, causing severe infestations where otherwise 
they would be so scarce as hardly to come to notice at all. 
This does not mean, however, that the mealybug outbreaks do not 
occur in southern California except in the presence of ants. More 
than 300 outbreaks of the citrus and other species of mealybugs were 
reported during the summer of 1916 in and about Pasadena by Dr. 
A. G. Smith, the local county inspector. The writer inspected 167 of 
these for ants, but, while the Argentine ant was present in 72 of 
them, and other ants in 16 more, there were no ants in the remaining 
79. Nevertheless, it is a fact that in Los Angeles County the enemies 
* of the citrus mealybug bring it under control early in the season and 
generally cause its almost complete disappearance when there are no 
ants present to prevent. 
27139°— 18— Bull. 647 3 
