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 larvae 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 

 larvae 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 larvae 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 larvae afre in evidence, 

 they probably will not be applied until some of the larvae 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 

 larvae 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 larva? 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 larvae survived. It was evident that unless they fed 

 on poisoned leaves continuously for some time they were not affected 

 at all. Unless the larvae 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 larvae 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 

 of arsenate of lead (paste), 3 pounds to 50 gallons of liquid, would 

 be of value in preventing injury by this pest. 



