THE MARGUERITE FLY. 45 



in temperature. Of interest, also, is the fact that the range of variation 

 in the two lots was the same. 



The newly emerged perfect female may be described as follows: head, 

 pale yellow, with a broad central longitudinal black band on the occiput: 

 antennae, black; thorax, grayish; macrochetse, black; wings, gi-ay, pale 

 at base, unspread; legs, black, with pale-yellow markings on femora and 

 tibiae; abdomen, pale yellow, dorsally and ventrally, with darker trans- 

 verse, broad bands, one on each segment; seta?, black; terminal segment, 

 black. 



Length of Life Cycle. 



The leng-th of a generation varies, owing to the variability of the stages 

 constituting it. The mean or average length of a life cycle, however, may 

 be obtained bj- combining the mean or average length of each stage. 



The average lengths of the periods constituting the Ufe cycle during 

 November, at a temperature at which marguerites are usually kept (see 

 temperature in connection with length of egg stage), are as follows: — 



Days. 

 Time elapsing between emergence of adult and oviposition, . . . IJ 



Length of egg stage, .......... 5 



Length of larval stage, .......... 13 



Length of pupal stage, .......... 14 



Average length of one generation, ....... 33J 



Number of Generations in the House. 

 Knowing the length of a generation, we can calculate the approximate 

 number of overlapping generations or broods which occur in the house 

 from the setting in of the cooler season, when the flies make their first ap- 

 pearance in the house, or when they reappear, or appear in greater numbers, 

 to about Easter, when most of the marguerites are sold out, or to the end 

 of May, in cases where the plants are grown for their bloom. Thus there 

 are at least four complete broods for the period between November 1 and 

 April 1, and at least six complete broods for the period between November 

 1 and June 1, for a hfe cycle of tliirty-three and one-half days. Owing to 

 the higher temperature during April and May there may be an additional 

 generation, or partial generation, for the period between November 1 and 

 June 1. 



Hibernation. 

 Is the insect able in some one of its stages, say pupa, to pass the winter 

 out of doors? This question is suggested by a letter from Mr. Walker 

 Holden. According to tliis letter the marguerites and feverfews in Mr. 

 Holden's greenhouse were badly infested by the insect during the winter 

 of 1911. The following spring these plants, as was the practice, were 

 removed from the house to the garden for the summer, and towards fall 

 furnished the cuttings for a new crop. That faU and winter (1911-12), 

 however, there were no signs of the insect in the greenhouse. In the spring 



