OF WASHINGTON. 



41 



of the seeds of this plant. I afterwards repeatedly found 

 these larvae at Manhattan and vicinity but failed to rear any 

 of the parent insects, although efforts to do so were continued 

 for several seasons. 



In November, 1889, the seeds of a Xanthium, probably X. 

 canadense, which occurs abundantly in the vacant lots in 

 Washington and on the Potomac flats, etc., were found to be 

 infested with a larva apparently identical with those previously 

 noted in Kansas. Better success was had in breeding these 

 larvae, and from seeds collected in the fall of 1889 and spring 

 of 1890 the mature insects named above were secured. The 

 exact date of emergence was not noted the flies being found 

 dead in the breeding cage about the ist of September.* 



FIG. i. Trypeta czqualis : a, Xanthium bur in longitudinal and cross 

 section, showing work of larva ; b, larva enlarged, with de 

 tails of anterior and posterior extremities still 

 more enlarged (original). 



The perfect insect appears, without doubt, chiefly in 

 August, during which month the burs of the Xanthium are 

 just forming, and can be easily pierced by the female in ovi 

 positing. 



In no case was more than one larva found in a bur, which 

 normally contains two seeds separated by a distinct and strong 

 septum. The seed proper of the Xanthium is rich in oil, and 

 possesses somewhat of the characteristic pungent odor of the 

 plant. 



The larva inhabits and feeds on this seed, which, in most 

 instances, was nearly consumed. (See Fig. i, a.) Full larval 



*The rearing and determination of this insect was recorded at the 

 October, 1890, meeting of the Society. 



