12 BULLETIN 598, U. S. DEPARTMENT OF AGRICULTURE. 
~~. 
ECONOMIC IMPORTANCE. 
Injury by this insect is intensive and not extensive. It is due to 
the gregarious larve of the early stages which strip branches and 
sometimes small trees of their foliage. The injury to young trees in 
particular may be severe. After the gregarious habit is lost the 
larve scatter so widely that the injury done by them is inconspicuous. 
Infestation by this insect so far as the writer has observed is not 
general even within an orchard. Several colonies of larve may be on 
one tree, but the writer has never seen a large tree completely stripped. 
Usually damage occurs in young orchards on which the codling- 
moth sprays have not been applied. The increasing importance of 
the cultivated walnut trees in the northeastern United States prob- 
ably will cause this pest to become correspondingly more important. 
CONTROL. 
Spraying with arsenicals is the usual recommendation for the con- 
trol of this pest. In orchards which have been thoroughly sprayed 
for the codling moth the writer has never noted an infestation. 
Nevertheless, the caterpillar soon becomes very hard to poison, and 
very large amounts are required to kill it in the later stages. 
If control measures are not adopted until the larvee are in evidence, 
they probably will not be applied until some of the larve are in the 
third or fourth instar. Spraying at this time is likely to produce dis- 
couraging results. Two trees infested with colonies of fourth-stage 
larvee were sprayed with arsenate of lead July 31, 1915; on one the 
poison was applied at the rate of 3 pounds (paste) to 50 gallons and 
on the other 5 pounds (paste) to 50 gallons. None of the larve died 
until two days later on the tree sprayed with the larger amount of 
poison, and not until three days later on the tree sprayed with the 
smaller amount. On the tree sprayed with the smaller amount about 
10 per cent of the larve survived. It was evident that unless they fed 
on poisoned leaves continuously for some time they were not affected 
at all. Unless the larve are confined on a sprayed tree they are very 
likely to migrate to another before eating enough to kill them. 
In the gregarious stages colonies of these larve are easily collected 
and destroyed. When the infestation is scattered throughout an 
orchard this method is much the cheapest that can be employed and is 
entirely effective. 
On young orchards which would not receive the spring spray ap- 
plications for the codling moth, an application about the last of June 
cf arsenate of lead (paste), 3 pounds to 50 gallons of liquid, would 
be of value in preventing injury by this pest. 
