June, 1922.] 



Leiby: Biology of Gnorimoschema. 



85 



The first moult takes place while the young larva is secluded in 

 the terminal bud of the goldenrod shoot and the succeeding moults 

 (five altogether) are undergone in the gall chamber, since the larva 

 never abandons the gall. During growth it was observed that the 

 excrement is packed in the apex and base of the gall but mostly in 

 the base (Plate VIII, Figs. 4, 6 and 8), the chamber always being 

 scrupulously clean. This detritus was carefully examined for the 

 moult skins upon a number of occasions and four head capsules rep- 

 resenting four additional instars were always found. The last moult 

 skin is always found either in the base of the gall chamber or adhering 

 to the pupa (Plate VIII, Fig. 6). 



The length of the instars was determined by measuring the size 

 of the head capsules and comparing them with the size of the heads 

 of a large number of larv?e during June and July, and further compar- 

 ing them with the length of the larvae. This data is given in Table I 

 and indicates that the length of the instars averages 8, 8, 9, T5 and 24 

 days respectively although the last instar includes a semiquiescent 

 prepupal period of about a week during which time the larva shrinks 

 perceptibly in size. No descriptions of the instars are given since all 

 stages are uniformly colored, a condition to be rather expected since 

 the larva spends the last four instars of its life in complete darkness. 



Table i. Number and Length of Larval Instars — Season 1914. 



The Pupa: The pupa averages 9-5 mm. in length. It is shiny 

 mahogany brown in color which changes to an almost jet black 

 (Fig. 6) just before the adult emerges. It shows no striking charac- 

 teristics in which it might differ from the usual lepidopterous naked 

 pupa. 



Biology and Habits. 



The writer has had occasion to follow the complete life-history of 

 this gall-maker during several years and to rear the insect from the 



