312 



THE XANTHIUM TRYPETA. 



{Trypeta cequalis Lw.) 



By C. L. Marlatt. , 



The species of Xanthium are such pestiferous weeds and are so wide- 

 spread in the TJuited States that a knowledge of any insect enemy of 

 importance becomes interesting. The plants of this genus are rank, 

 strong growers, and possess a pungent odor which seems to protect 

 them in a measure from insect attack, as but few insects are known to 

 feed on them as compared with other similarly widely distributed and 

 abundant plants. 



But two insects, I believe, have been hitherto recorded to feed upon 

 the Xanthium. These are Bhodobcenus tredecimpunctatus ID. {-Spheno- 

 pliorus pulchellus Schoen.), an account of which, with figures, is given 



in Eiley's Third Eeport on the Insects of 

 Missouri, p. 60, and Syphocoryne xanthi 

 (Est., an aphid which occurs on the leaves, 

 and which was described by CEstlund in 

 the Fourteenth Eeport of the Geological 

 Survey of Minnesota, p. 36. In addition 

 to these. Professor Eiley has reared Gor- 

 tyna nitela Guen. from the stems, and has, 

 from Mr. Webster, Cecidomyiid larvae 

 from the roots. Mr. Schwarz informs me 

 that he has reared an undescribed Cur- 

 culionid {Baris sp.) from the roots, and 

 I have taken a very handsome Ceram- 

 bycid (Dectes spinosus Say) on the plant 

 in Kansas under circumstances which 

 leave no doubt but that the Xantliium is 

 its normal food plant. I have also found infesting the seed-pods of 

 this plant a microlepidopterous larva, which I have been unable to rear. 

 Of greater promise of economic importance, perhaps, than any of these 

 is the Trypeta named above, the larvae of which I have known for a 

 number of years to infest the Xanthium seeds, but which, until the last 

 summer, I have not succeeded in rearing to the adult stage. A full ac- 

 count of this insect is given in ]S"o. 1, Vol. ii, of the Proceedings of the 

 Entomological Society of Washington (pp. 40-44). 



It seems to be as widely distributed as its food-plant, as I have found 

 the larvae both at Manhattan, Kans., and in the District of Columbia, 

 and the adult is recorded from Illinois, Ohio, and Maryland, and spec- 

 imens slightly differing but probably of the same species have been 

 taken in Colorado. A single female was also recently sent to Professor 

 Eiley, for determination, by Professor Gillette, of Iowa. 



The accompanying illustrations will give a good idea of the habit and 

 appearance of the larva. (Fig. 276 ) 



Fig. 21 .—Trypeta cequalis : a, sectional 

 view of theXanthiftm bur, sliowrng larva 

 in position ; &, larva enlarged with oral 

 and anal plates still more enlarged with 

 details of the anal and anterior stigmata 

 (original). 



