28 BULLETIN" 647, U. S. DEPARTMENT OF AGRICULTURE. 



and 18.7 per cent of those on ant-excluded trees, showing a slight 

 tendency toward worse infestation under ant attendance. The 

 marked tendency of mealybugs to establish themselves under the 

 sepals of the young fruits and in similar situations to secure sheltered 

 feeding places must be taken into account when considering the 

 subject of the transfer of mealybugs by ants to establish new colonies. 



Between May 24 and July 24 mealybug infestation rapidly in- 

 creased on the trees to which ants had access, while it decreased, 

 with slight fluctuations, to an almost insignificant amount on those 

 from which ante were barred. From July 24 to September 2 there 

 was a slow reduction in the amount of mealybug infestation on the 

 art-traversed trees, an increasing number of mealybugs' remains indi- 

 cating increased effectiveness of the natural enemies, which had 

 become more numerous following the food supply. On the trees 

 from which the ants were barred the mealybug infestation in the 

 same period, with minor fluctuations in which the highest point 

 was slight infestation of 7 per cent of the fruit, was maintained at a 

 negligible amount. 



The most important early activity of mealybug predators occurred 

 on the very small fruits, these insects occurring with mealybugs 

 under the sepals as soon as the mealybugs arrived there and pre- 

 venting the growth of infestations from these spots. From July 24 

 to the close of the experiment, September 12, the number of preda- 

 tory enemies, again following the available supply of food insects, 

 was greater on the trees traversed by the ants than on those from 

 which ants were barred, there being from five to eight times as many 

 on the former as on the latter trees at the times examined. The prin- 

 cipal enemies of the mealybugs occurring on these trees were Coc- 

 cinellidae, Hemerobiidae, Chrysopidae, Pyralidae, and Syrphidae. 

 During this latter period of the experiment, following the decrease 

 in percentage of infested fruits on the ant-traversed trees, the in- 

 creasing effectiveness of the mealybug enemies was manifested in the 

 occurrence of an increasing number of fruits which had been rid 

 of mealybugs, their previous infestation being indicated by bits ot 

 cottony secretion, sooty mold, etc. 



Experiments III and IV. 



Two other experiments conducted at Alhambra, Cal., with nursery 

 trees and potted seedling orange trees brought out very similar 

 results. The nursery trees, owing to too late transplanting, failed 

 to thrive and did not become very heavily infested with mealybugs, 

 but showed less plainly but quite as certainly the results of ant 

 attendance in increasing these insects. 



In the experiment on potted orange seedlings, 6 of the young 

 plants were infested artificially with mealybugs, and on May 17, 



