UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 647 
Contribution from the Bureau of Entomology 
L. O. HOWARD, Chief 
Washington, D. C. 
May 3, 1918 
THE ARGENTINE ANT 1 IN RELATION TO CITRUS 
GROVES. 
By J. R. Horton, Scientific Assistant, Tropical and Subtropical Fruit Insect 
Investigations. 3 
CONTENTS. 
Introduction 1 
General belief as to damage to orange trees. . . 2 
General account of orange culture in 
Louisiana 4 
Distribution of the ant in the orange groves 
of the United States 7 
Feeding habits of the ant 8 
Relations with insects injurious to citrus trees 15 
Relations with insect enemies of scales and 
aphids 48 
Page. 
Nests and protective structures of the Argen- 
tine ant 52 
Cultural conditions in ant-invaded vs. ant- 
free orange groves in Louisiana 56 
Demonstration in improvement of ant- 
invaded groves in Louisiana 57 
Experiments in controlling the Argentine ant 60 
Summary and conclusions 71 
INTRODUCTION. 
The Argentine ant {Iridomyrmex humilis Mayr) is a native of 
tropical America, occurring in Argentina, Brazil, Chile, and Uru- 
guay. It was first introduced into the United States at New Orleans 
about 30 years ago and was fairly numerous in parts of that city as 
early as 1891. 3 A few years later it had become established thor- 
oughly in and around New Orleans and was causing great annoyance 
as a household, garden, and field pest. Early it was carried to Cali- 
fornia, where it has become established widely. It is especially 
numerous in parts of the citrus districts of Los Angeles and River- 
side Counties and in the city of Los Angeles and occurs as far north 
as San Francisco and as far south as San Diego. 
1 For a discussion of other phases of the Argentine ant problem see Department of 
Agriculture Bulletin No. 377, by E. R. Barber, entitled " The Argentine Ant : Distribution 
t^Jf. and Control in the United States." 
2 Transferred to Cereal and Forage Insect Investigations, Oct. 1, 1917. 
8 Foster, Ed. The introduction of Iridomyrmex humilis into New Orleans. In Jour. 
Econ. Ent., v. 1, p. 289-293. 1908. 
Note. — This bulletin is of especial interest to citrus growers in the southeastern States 
and generally to the public in that section, 
27139°— 18— Bull. 647 1 
