THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 47 



all others. Ants, with scales, also were traced to underground tun- 

 nels, which led neither to tree roots nor to any plant roots on which 

 the scales could live. 



Aphids, too, are transported only when the infestation is very 

 heavy. The largest numbers carried were upon maple and elder 

 trees, on which aphis infestation persisted somewhat longer than on 

 orange trees because of more rapid parasitism of the orange-infesting 

 species. A great majority of the aphids carried were dead. Since 

 almost all are destroyed by parasites, some undoubtedly contain 

 parasites when taken by the ants, but the number thus destroyed 

 is too small to reduce the effectiveness of these enemies. The destina- 

 tion of the aphids carried was generally the underground nest, Only 

 a very small percentage of the ants carry these insects up tree, 

 and, when traced, these always havj gone into one of the ant shelters 

 for rest or, ultimately, retraced the^r steps down the tree. 



Experiments have been tried several times to induce the ants to 

 remove scales and aphids from unsuitable food to a place where they 

 could thrive. As an example of these experiments, about two dozen 

 elderberry stems, very heavily infested with aphids, were on one 

 occasion placed in the midst of thousands of ants at the base of an 

 elderberry tree and examined at intervals thereafter. At the end 

 of an hour aphids were leaving the stems, many were scattered about 

 in the short grass, and a considerable number of others were travel- 

 ing up the tree trunk. A great majority of the ants paid no atten- 

 tion to these wanderers, but a few followed and stroked individual 

 aphids while in motion. One such ant, becoming impatient after a 

 few minutes of unrewarded effort, seized an aphid by a leg and 

 pulled it about this way and that for a distance of fully a foot, when 

 it let go and went its way. 



Similar experiments were performed with mealybugs, infested 

 stems being cut and placed among numerous ants in pots containing 

 vigorous young orange trees. The ants would attend and stroke these 

 mealybugs indefinitely, but in not a single instance did one transport 

 a mealybug from a dying stem to the flourishing growth of the 

 young orange tree. Many of the mealybugs would wander off the 

 dry stems, and some of them would find their own way sooner or later 

 into the healthy tree. 



On one occasion, in California, a good opportunity was presented 

 to the ants to assist mealybugs to regain trees from which they had 

 been knocked by spraying with water under high pressure. The ant 

 invasion was from " very heavy " to " extremely heavy " in about 70 

 per cent of the trees examined, the remainder having " light " or 

 " very light trails. Some of the mealybugs hit by the water were 

 27139°— 18— Bull. 647 4 



