6 



CIRCULAR 4 6 4, U. S. DEPARTMENT OF AGRICULTURE 



As the habits and the variable mortality of the gypsy moth and its 

 food-plant limitations cause wide differences in its abundance in 

 various parts of the infested area, it has seemed that the damage done 

 and the possibilities of greatest future injury could be gaged most 

 accurately by determining the defoliation caused by the species over 

 the area as a whole. The total acreage showing from 25- to 100-per- 

 cent defoliation each year beginning in 1924, when defoliation was less 

 than in any previous year, is as follows: 



Year Acres defoliated 



1924 825 



1925 48, 560 



1926 80, 822 



1927 140, 920 



1928 262, 514 



1929 551, 133 



1930 288, 225 



Year Acres defoliated 



1931 204, 720 



1932 286, 395 



1933 397, 730 



1934 492, 361 



1935 540, 769 



1936 428, 622 



Figure 2.— Life stages of the gypsy moth: A, Female moth; B and F, pupae; C, larvae or caterpillars; 

 D, male moth; E, egg mass. All about three-fourths natural size. 



The danger of reinfestation of the barrier zone depends largely on 

 the severity of infestation east of the zone. In the last 3 years the 

 areas of defoliation were smaller in eastern Massachusetts and certain 

 sections of southeastern New Hampshire, which comprise most of the 

 older infested territory. In the same years heavy defoliation was 

 noted much farther west in Massachusetts, and in 1934 and 1935 

 extensive areas of complete defoliation occurred in the Connecticut 

 River Valley and the adjoining territory about 20 miles from the zone. 



LIFE HISTORY 



The gypsy moth passes through four stages — the egg, the larva or 

 caterpillar, the pupa, and the adult or moth (fig. 2). There is one 

 generation a year. The times of the year when the different forms 

 may be found in the field are shown in figure 3 . 



