Aphids Injurious to Orchard Fruits, Etc. 39 
Following the other plan, spraying is not done until the insects 
actually have become troublesome, which does not occur as a rule 
until after the foliage is well out. With species that cause the leaves 
to curl this is too late to obtain much benefit from spraying. In view 
of the more or less irregular occurrence of aphids many growers will 
prefer to delay treatment until the insects actually are present on 
Fig. 31.—The adult syrphid fly Allograpta obligua. Much enlarged. (Davis.) 
the plants in destructive numbers, and in the case of those species 
which do not curl the leaves to any extent this plan will be satis- 
factory. Care should be taken, however, to treat the aphids promptly 
when they are found to be becoming abundant. It is a question 
for the grower to decide whether under his conditions danger of 
aphid injury, especially by the leaf-curling species, makes the bud 
application desirable or whether this danger is so small that he is war- 
ranted in taking chances on the insects becoming troublesome. Ex- 
amination of the plants to determine the abundance of winter eggs 
and young stem-mothers on the opening buds should be of assistance 
in this connection, though abundant winter eggs are not always fol- 
lowed by aphid abundance, since many may succumb to unfavorable 
weather conditions. 
INSECTICIDES. 
INSECTICIDES MADE FROM TOBACCO. 
CommeEerctAL NIcoTInE SOLUTIONS. 
Aphids are killed by surprisingly small quantities of nicotine in 
water, and because of the entire safety with which it may be applied 
to plants nicotine is better suited than other sprays to control these 
