THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 41 



excretion in this secondary manner, especially when other food is 

 scarce in the trees. If any large proportion of the white-fly excre- 

 tion were taken by the ants, however, the sooty-mold fungus would 

 be by so much the less prevalent in ant-invaded trees ; this, however, 

 is not the case. The ants do prevent to a very large extent the col- 

 lection of excretory matter and the formation of sooty mold after 

 mealybugs, even inducing such rapid excretion in certain young 

 stages that the mealybug is unable to form the wooly covering, its 

 body remaining almost naked and pink. 



Effect of the Ant on Abundance of the White Fly. 



An experiment to determine the effect of the ants on abundance of 

 white flies was started on April 25, 1914, a young orange tree with 

 S38 white-fly eggs being banded to exclude ants and a similar tree 

 with 1,474 eggs kept accessible to ants for comparison. The per- 

 centages of young stages of the white fly dying from unknown 

 causes and the quantity of new growth on the two trees were noted 

 at every examination to make sure that the difference in white-fly 

 infestation was not due to varying food conditions. 



On May 13 there were on the tree from which ants were excluded 

 949 sound and 113 dead larvae and pupse and 189 unhatched eggs; 

 on the tree that was accessible to ants there were 434 sound and 109 

 dead larvse and pupse and 112 living eggs. Between May 13 and 

 June 12 the nonbanded tree was merely kept under surveillance by 

 scouting ants, but on June 12 white-fly emergence was at its height 

 and the ants had formed a heavy trail into the tree, where they were 

 capturing the emerging adults. Living white-fly larva? and pupse 

 were comparatively scarce and about equal in number on both trees. 

 The remarkable thing was, however, that on the ant-invaded tree 

 there were 167 empty pupa cases from which white flies had emerged 

 and only 8 of the adult white flies, whereas on that from which ants 

 were excluded there were 151 empty pupa cases and 130 of the 

 emerged adults. In other words, the nonbanded tree was swarming 

 with ants, some of which were carrying adults, and only 4.51 per 

 cent of the emerged adults remained on the tree, whereas on the tree 

 from which ants were excluded almost the same amount of emergence 

 had occurred and 86 per cent of all the emerged white flies were still 

 on the leaves. 



From June 12 to about the middle of August the white flies in- 

 creased faster on the tree from which the ants were excluded than 

 on the other. On July 1 there were 5,435 living young on the 

 former and only 1,919 on the latter. The percentage of dead was 

 practically the same on both, being 12.9 per cent of all young on 



