THE ARGENTINE ANT IN RELATION TO CITRUS GROVES. 43 
and chiefty 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, 
J 914, 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 difficulty. 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 ma}^ 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 was 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- 
damia convergens Guerin) and a few syrphicl-fly larvse also occurred 
on the tree. 
At Duarte, Cal., 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. 
