SUMMER NUMBER 27 
been customary with crews spraying for whitefly or purple scale. 
A great advantage of spraying is the possibility of combining 
the control of aphids with that of whitefly, scale, thrips, rust 
mite, or red spiders. 
(8) Begin the fight in the fall. Aphids can be fought most 
economically during the winter. The first step in preparation 
for next year’s fight (we can see no valid reason on which to base 
a hope that they will not again appear in destructive numbers 
next season) is to employ every means consistent with good 
grove practice to throw the trees into complete dormancy in the 
late fall, about November in most sections. Then during 
December and January watch the trees carefully and destroy 
every aphid found. It would probably be an excellent idea to 
cut off those occasional sporadic sprouts that start out on young 
trees. Make every effort to have the groves free of aphids by 
the first of February. In the spring, as early as is considered 
reasonably safe from the standpoint of danger from frost, do 
everything consistent with good grove practice to rush the 
growth along and get a good crop of new foliage out before the 
aphids become numerous. 
(4) With the exception of the fungus Empusa, the natural 
enemies of the aphid are generally incapable of checking an out- 
_ break. The lady beetles and syrphus fly larvae destroy many 
aphids, but their multiplication is checked by numerous super- 
parasites. The hymenopterous parasite, which is usually the 
most effective check on the increase of the melon aphis:on citrus, 
has been repeatedly bred out on the green aphis, but its occur- 
rence on this species in the groves is still so uncommon that the 
presence of any considerable number of dead, swollen aphids 
with emergence holes is a sure indication of the presence of the 
melon aphis. 
OTHER Hosts. In addition to spiraea and citrus the aphid 
occurs occasionally on a number of hosts. Three of them are 
quite common in citrus groves and are often quite heavily in- 
fested. Perhaps the most dangerous of these is the “Jerusalem 
oak” (Chenopodium sp.). Even more heavily infested is fireweed 
(Erechtites hieracifolia (L) Raf.) but it is not as common in 
citrus groves, being found mostly on lower more moist land es- 
pecially when newly cleared. These two plants should be cut down 
before a grove is dusted or sprayed. Cudweed (Gnaphalium 
sp.) is a very common winter and early spring annual in citrus 
