THE CANKERWORMS 9 



suffer the most severe losses. In orchards which are well cared for 

 and consistently sprayed with arsenicals, there is little opportunity 

 for the cankerworms to gain a foothold. Such orchards are usually 

 comparatively immune from attack, even during a period when 

 cankerworms are abundant in the immediate neighborhood. As far 

 as orchards are concerned, the cankerworm may therefore be rated 

 as a pest which may be easily controlled, but which during periods 

 of abundance may do serious damage if the orchards are neglected. 

 As a shade-tree pest, the cankerworm is periodically of great im- 

 portance. 



FALL CANKERWORM. 



DESCRIPTIONS. 



EGG MASS. 



Counts were made at Wallingford, Conn., of the number of eggs in 

 35 egg masses collected in the field in 1919 and 1920 and 76 egg 

 masses laid in captivity in the fall of 1919. In the field-collected 

 eggs the maximum number in a mass was 244, the minimum 3, and 

 the average 129.3; in those laid in captivity the maximum was 408, 

 the minimum 4, and the average 101.2. Thus the number of eggs 

 in a single egg mass is seen to vary from a very few to several hun- 

 dred, although the largest masses probably resulted from the efforts 

 of more than one moth. The largest cluster noted, that of 408 eggs, 

 is known to have been contributed to by two females. 



Britton (33) reports for 100 egg masses collected in the field an 

 average of 94 eggs, and for 65 laid in captivity an average of 148. 



The eggs are laid in various places, but usually on the smaller 

 branches and twigs, frequently very near the tips. The moths have 

 been known to deposit their eggs on fence posts and the sides of 

 houses. The masses are often found on tree trunks, especially if a 

 barrier has interrupted the progress of the moth. On a tree trunk 

 or other nearly flat surface, they form a flat mass; on a very small 

 twig the cluster is cylindrical, frequently encircling the twig com- 

 pletely (PL I, B ; II, B). The eggs are laid in straight rows follow- 

 ing the length of the twig, each egg opposite the space between two 

 eggs in the adjacent row, and are placed so closely together that their 

 natural circular outline frequently becomes slightly hexagonal where 

 they come in contact at the top. 



The individual egg is somewhat cylindrical, rounded at the base, and smaller at 

 the base than at the top, which is slightly convex with a small pit at the 

 center. Measurements of a number of eggs from several different masses 

 averaged as follows : Height 0.70 millimeter, width at top 0.50 millimeter, width 

 at base 0.42 millimeter. In general color the egg is an ashy gray which is 

 lightest at the base and on the sides. The greater part of the top, or cap, of 

 the egg is a darker gray to brown, having near the outer edge a depressed 

 circle within which is a narrow circle of brown. The surface of the cap of 

 the egg is very minutely and irregularly sculptured, with a few of these fine 

 lines radiating in an irregular fashion from the central depression. 



LARVA. 



First stage. — Width of head 0.36 to 0.39 millimeter, average 0.37 millimeter ; 



l length when newly hatched 1.84 millimeters, when full-fed about 4.5 millimeters. 



General color of newly hatched larva yellowish green to olive green. Head 



75522°— 24 2 



