44 BULLETIN 647, U. S. DEPARTMENT OF AGRICULTURE. 



Again, at Sierra Madre, Cal., on June 16, scattered groups of 

 aphids attended by ants on several trees revealed a parasitization of 

 92.1 per cent. On one of these trees 14 syrphid larvse with 1 coccinel- 

 lid larva and 15 or 20 ants were found working on the same groups 

 of aphids. 



The relations of the Argentine ant to an aphid commonly occuring 

 on elder in Louisiana were observed especially because of the excep- 

 tional abundance attained by this plant-louse early in the summer 

 and its abundant attendance by the ants. During March and April 

 the aphids become too numerous for the trees to support and thou- 

 sands fall to the ground, covering the grass under the trees and 

 crawling back up the trunks in large numbers for days at a time. 

 This aphid is progressively destroyed by predacious enemies and 

 especially by parasites, until by the middle of June it invariably has 

 been reduced to an insignificant number, which gather about the 

 bases of the stems and leaves, where the best possible shelter occurs. 

 On April 24, 1914, the comparatively few shells and aphids remain- 

 ing on one of these trees were counted. There were only 1,667 in 

 all, 529 of which were living, 68.4 per cent being parasitized. The 

 principal parasite concerned was identified by Dr. L. O. Howard as 

 a species of Aphidencyrtus. 



On March 24, 1914, 9 robust young elder plants in pots were in- 

 fested with the aphids and placed where the ants could get to them. 

 About a month later. May 7, there were on all plants 2.436 living and 

 apparently sound aphids and 985, or 28.7 per cent, parasitized. All 

 parasitized shells were removed, and. on May 13, 1.18 per cent more 

 aphids, parasitized since the previous examination, were removed, 

 after which ant- were excluded from 4 of the plants, on which were 

 418 sound aphids. and allowed access to the remaining 5, on which 

 were 535 aphids. 



On June 3 only 47 living aphids remained on the ant-free plants, 

 but 119 were on the ant-invaded plants: and by June 16, at which 

 time most all the aphids had disappeared from the large elder trees 

 thereabouts, not a living aphid was left on any of the little plants. 



In another experiment 2 robust elder plants were colonized with 

 aphids on March 24. One plant was given 187 aphids and placed in 

 a large trail of ants, and the other was given 185 aphids and placed 

 where the ants could not get to it. By April 8 there were 3,194 

 living, apparently sound aphids on the ant-attended plant, an in- 

 crease in 15 days of 1.708 per cent: and on the ant-excluded plant 

 there were 2,514. an increase of 1.364 per cent. The more rapid rate 

 of increase on the ant-attended plant seemingly was due to the activi- 

 ties of the ant, other factors being apparently the same in both cases. 

 The number of living sound aphids soon began to decrease on both 



