THE PEAR LEAF-V/ORM. 



15 



the larvaB had hatched by April 24, and the largest number were enter- 

 ing the soil about May 20, giving an average larval period of about 

 26 days. The table shows an average of 28.1 days, and the only 

 larva that was reared to maturity (No. 3) occupied 26 days from egg 

 to cocoon. This is a longer period than at Walnut Creek, Cal. (18.4 

 days) where the larvae were reared normally on the trees, and a 

 shghtly shorter period than at San Jose (31.6 days), where the larvae 

 were reared under conditions similar to those in Washington State. 



THE COCOON AND PUPA. 



In order to determine how deeply the larvae penetrate the earth 

 for the purpose of spinning their cocoons, 60 full-grown larvss were 

 placed in a screen cage sunk into the soil and filled with 7 inches of 

 average orchard soil April 30, 1913. By May 3 aU the larvae had 

 burrowed and on Jmie 18 the soil was examined with the results 

 enumerated in Table IX. 



Table IX. — Depth in soil for cocooning of the pear leaf-worm, Walnut Creek, Cal., 1913. 



Number of 

 cocoons 

 found. 



Inches be- 

 low soil 

 surface. 



46 

 2 



4 



1 



Otol 

 lto2 



2 to 3 



3 to 4 



Fifty-three out of 60 were thus accounted for, and therefore 88.3 

 per cent of the larvae spun cocoons. It is evident from Table IX 

 that the great majority spin their cocoons not more than 1 inch below 

 the surface. In the above instance this majority was 86.8 per cent. 



Table X shows the depth in the soil at which the cocoons are 

 spun in Washington. On May 21, 1915, 93 larvae just ready to enter 

 the earth were placed in an open jar on top of 6 inches of fairly 

 closely packed, moist, sandy soil, which is typical of the orchards 

 of the region. In a few days the larvae had aU disappeared and 

 on June 1 1 the soil was sifted and 71 cocoons were recovered. Thus 

 76.3 per cent of the larvae spun cocoons, the others being found 

 dead near the surface. The depths at which the cocoons were found 

 are given in Table X. 



Table X. — Depth in soil of cocoons of pear Icaf-vorvi, Wenatchee, Wash., 1915. 



Number of 

 cocoons 

 found. 



Tncbcs 

 bi'low 

 .siiifuco. 



39 



24 



7 



1 



Otoi 

 i tol 

 lto2 

 2 to 3 



