THE AEGEXTIXE AXT IN EELATIOX TO CITEUS GBOVES. 43 



and chiefly the internal parasites, have so reduced it by July or 

 August that it is difficult to find specimens. 



The following examples will serve to illustrate the ineffectiveness 

 of the ant against the parasites of the orange aphis: On April 22, 

 1914. in an orange grove overrun with ants at Happy Jack, La., 

 aphids were very numerous, averaging about 34 per leaf of the worst 

 infested leaves, and undoubtedly would have done much damage 

 had their increase continued long at the same rate. Even at this 

 time, however, the aphid shells punctured by parasite exit holes indi- 

 cated a parasitization of 29.7 per cent. Three hymenopterous para- 

 sites seen ovipositing in the aphids among the ants were watched 

 until they had parasitized nearly every aphid on their respective 

 leaves. While ovipositing in the aphids these little insects nimbly 

 avoided the ants without flying. On May 15 living aphids could be 

 found on these trees only with difficult}'. In the meantime, too, 

 many of the parasitized remains previously seen had been blown 

 from the leaves, so that there was very little evidence that aphids 

 had ever been numerous there. 



On April 28, 1915, 15 per cent of the ant-attended aphids in an 

 orange grove at Ollie. La., had been parasitized, but living aphids 

 were still rather numerous, averaging 20 per leaf on those leaves 

 examined. By May 12 the aphis infestation in this grove had de- 

 creased more than 50 per cent, and 49 per cent of the remaining 

 aphids were parasitized. On May 27 an examination of twenty-five 

 times as many suitable leaves as before revealed an average of only 

 about two aphids per leaf, and 92.6 per cent of these were parasitized. 

 The foregoing observations are merely examples of what may be 

 seen annually in almost any grove in Louisiana in which ants and 

 aphids occur. 



At Alhambra, Cal., early in April, 1916, a trail of ants w T as found 

 leading to flourishing small colonies of aphids on the new sprouts 

 of an orange tree that had been cut back about 4 feet from the 

 ground. The aphids were very numerous and not more than one per 

 group showed evidence of parasitism. On April 21 fully half of the 

 aphids had disappeared from this tree and 79.6 per cent of the re- 

 mainder were parasitized. Ten aphid-feeding lady-beetles (Hippo- 

 Jamia convergens Giierin) and a few syrphicl-fly larvae also occurred 

 on the tree. 



At Duarte, Gal., 20 young ant-invaded orange trees, badly infested 

 with aphids on the new leaves about the middle of April, were almost 

 completely free from them when examined on May 19. The few 

 aphids remaining alive were being attended by the ants, but not 

 one-tenth of 1 per cent of what had previously been present remained 

 on the trees at this time, and discolored and dried shells with their 

 parasite exit holes were everywhere present. 



