310 Report of the Entomologists of the 



looked for and destroyed. If the orchard has been badly infested 

 it will pay to make a special search for them. 



Destroying the caterpillars. — Many methods have been sug- 

 gested for destroying the caterpillars but there are three especially 

 feasible ones, which, if carefully carried out, will usually prove 

 effectual. 



First, spraying with an arsenical compound. — Any good arseni- 

 cal will answer the purpose if applied before the caterpillars are 

 half-grown. Some of the principal arsenical insecticides are 

 Paris green, green arsenite and arsenite of lime. For a discussion 

 of green arsenite and arsenite of lime see Bulletins 143 and 152 

 of this Station. A third arsenical, arsenate of lead, has been found 

 by the Gypsy Moth Commission of Massachusetts to be especially 

 effectual against the gypsy moth and to be almost harmless to 

 foliage. The formula is as follows: ]1 ounces acetate of lead, 4 

 ounces arsenate of soda, 150 gallons of water. The directions for 

 making arsenate of lead as given by Professor C. H. Fernald^^ are 

 as follows: "Arsenate of lead is easily prepared by putting 11 

 ounces acetate of lead in 4 quarts of water, in a wooden (not 

 metal) pail, and 4 ounces of arsenate of soda (50 per ct.) in 2 

 quarts of water in another wooden pail, and when entirely dis- 

 solved mixing them in a hogshead containing 150 gallons of water, 

 when a chemical reaction will take place forming arsenate of lead 

 in a fine white powder in suspension of water. If cold water be 

 used in the wooden pails, the solution of the acetate of lead will 

 require a little time, but, however, if the water be hot, it will dis- 

 solve very quickly. It is customary to add from 2 to 4 quarts of 

 glucose to the above amount of water. If it is desired to use larger 

 proportions of the arsenate of lead, it is only necessary to use more 

 acetate of lead and arsenate of soda, but always in the proportions 

 given above." To ensure success in spraying two points should be 

 kept in mind, namely, promptness and thoroughness. The poison 

 will be much more effective if applied before the caterpillars are 



32 Ann. Kept. Mass. Bd. Agr. 1897. 



