CONTROL OF ARGENTINE ANT IN CALIFORNIA. 
to adjacent trees. The chief damage done by the Argentine ant in 
California citrus orchards has been through its relation to mealybug 
infestations, particularly the common mealybug, Pseudococcus citri 
(Risso) . Prior to the reported presence of this ant in the Southwest, 
one species of mealybug was recorded as a serious citrus pest in only 
three or four limited districts, where it was characterized by sporadic 
outbreaks which would quickly disappear. In the last decade, 
which is contemporaneous 
with the Argentine ant inva- 
sion, the severe infestation 
of the common mealybug has 
increased many hundred per 
cent and districts have been 
invaded from which mealy- 
bugs were never before re- 
corded. 
In the course of investiga- 
tions under the direction of 
the senior writer to establish 
effective control of the com- 
mon mealybug, Pseudococcus 
citri (Risso) , it was discovered 
that the Argentine ant not 
only brings about increased 
severity of infestation but 
causes the mealybug to per- 
sist year after year. It was 
furthermore discovered that 
the common mealybug was 
attacked by many predatory 
insects, some of such high 
efficiency that in ant-freed 
territory they were capable 
of keeping the mealybug un- 
der commercial control ex- 
cept at those infrequent periods normal in the "ups and downs 7 ' of 
biologically controlled pests. Demonstrations carried out in several 
mealybug-ant infested orchards in the San Gabriel Valley during the 
years 1915 and 1916, in which alternate rows were kept free of ants, 
proved that trees rid of ants quickly become freed of mealybugs, 
although on adjacent ant-attended trees the mealybug infestation 
persists. The results of these demonstrations are verified by the 
fact that in every experiment performed by the writers during the 
period of 1915-1920 equally good results have been obtained. The 
Fig. 1.— Ants attending a group of mealybugs. Their 
almost constant presence protects the mealybug from 
its natural enemies. 
