26 
BULLETIN 647, U. S. DEPARTMENT OP AGRICULTURE. 
from which ants were excluded, remaining, on July 17, about one- 
third as heavy as on May 17. 
Up to July 17, therefore, the presence of the ants had a very 
notable effect in increasing and maintaining mealybug infestation. 
On this date the band was removed from one of the branches so that 
reinfestation under ant attendance might be observed, and one of 
the branches previously free to ant attendance was banded. No 
marked results were obtained from this test. As indicated in Table 
IV, a slight reinfestation of mealybugs occurred on all the branches 
free from infestation on July 17, but there was a general decrease of 
infestation on both types of branches and on the entire tree through- 
out August. The only living mealybugs remaining on either set of 
branches during August were young which were scattered over the 
leaves, the insects being destroyed by their predatory enemies before 
reaching maturity, and by September 2 the entire infestation on the 
tree was reduced to an insignificant amount. In other words, on 
this particular tree the effect of the ant in increasing and maintain- 
ing the mealybug was marked up to the middle or end of July, but 
this effect was practically lost during August. 
Table IV.— Effect 
of the Argentine 
ant 
on 
abundance 
of mealybuas 
on 
orange. 
Los Angeles County, Gal., 1916. 
Ants present. 
Ants excluded. 
From Apr. 14 to Sept. 2. 
From July 17 to 
Sept. 2. 
From Apr. 14 to Sept. 2. 
From July 17 to 
Sept. 2. 
Date. 
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1 All of the leaves examined. 
The efficiency of natural enemies, as affected by the ant, was seen 
in the first period of the experiment, from April 14 to July 17. 
From April 14 to May 17 the number of mealybug enemies occurring 
on the branches from which ants were excluded did not differ widely 
from that on branches to which ants had access; yet, although by 
the latter date these enemies had reduced greatly the number of 
mealybugs on branches kept free from ants, their effect on mealy- 
bugs attended by ants was negligible. It appears that the mealybug 
predators are able to avoid capture by the ants, but are incapable 
of reaching the mealybug groups closely attended by them. 
