2 BULLETIN 965, U. S. DEPAETMENT OF AGRICULTURE. 



merely as ''an ant" whose presence was believed in no way detri- 

 mental to the trees. The role of the Argentine ant as an orchard 

 pest in California was discovered by Mr. J. D. Neuls and the senior 

 writer in 1915 while conducting an investigation of the common 

 mealybug, and its very direct bearing on the control of the mealybug 

 was conclusively proved by an extended series of experiments. This 

 immediately led to an investigation into methods of ant control with 

 which the junior writer became associated in 1917. The great success 

 which attended these experimental efforts led to control demonstra- 

 tions of considerable proportions in severely ant-infested communi- 

 ties and proved a stimulus to widespread interest in the pest. The 

 demand for relief which followed this awakened interest has already 

 resulted in the treatment of several thousand acres, from a very large 

 part of which the ants have been totally eradicated. This bulletin 

 presents the results of the various remedial methods pursued during 

 the period 1915-1920 and gives full instructions for the control and 

 eradication of ants in the citrus orchards of California. 



RELATION OF THE ANT TO THE CITRUS INDUSTRY. 



The spread of the Argentine ant in California bears an important 

 relation to citrus growing, a relation certain to become more promi- 

 nent with wider distribution and long-established infestations. The 

 very severe damage which this pest can sometimes do in citrus 

 orchards has been impressively stated by Newell and Barber ^ as 

 follows: The bearing qualities of an orchard are severely impaired 

 by the second season of infestation, the crop is almost entirely lost 

 by the third season, and the trees are dying by the fourth year of 

 infestation. This conclusion is based on conditions in Louisiana, 

 and in this respect it should be noted that no systematic effort is 

 made in that State to control citrus scale pests. Such extreme 

 damage has never been observed under California orchard conditions 

 where fumigation and other insecticidal control measures are prac- 

 ticed constantly. 



The damage to trees in ant-infested orchards in California does not 

 arise from direct attacks on the blossoms, fruits, and roots, as has 

 been reported from some regions, but is attributable very largely 

 to its so-called symbiotic manner of living with mealybugs, aphids, 

 and various scales, which results in their increase beyond all custom- 

 ary proportions. The constant attendance of the ant protects the 

 mealybugs or scales from their natural enemies and results in their 

 abnormal increase. (See fig. 1.) The degree of infestation is 

 further stimulated and extended through the fact that the ant 

 distributes these injurious insects to other parts of the tree or even 



> Newell, Wilmon, and Bakber, T. C. the argentine ant. U. S. Dept. Agr., Bur. Ent. Bul. 

 122, p. 192. 1913. 



