THE IMPORTED CABBAGE WEBWOKM. 



31 



cultivated plants, such as " Japanese radish," are subject to attack 

 and injury. Among weeds and wild food plants are the common 

 shepherd's purse (Bursa [Capsetta] bursa- pastoris) and "pussley" 

 or "cutter's grass," otherwise purslane (Portulaca oleracea). 



NATURAL ENEMIES. 



Natural enemies of cruciferous insect pests are of great value in 

 keeping their hosts in check, and some dependence must be placed 

 upon these agencies in restraining the undue multiplication of this 

 webworm. Indeed, there is evidence that they do hold it in check 

 in many regions, al- 

 though they have not 

 prevented its natural 

 spread. 



In spite of the short 

 time that we have 

 known of its occur- 

 rence in this country 

 as a pest — since about 

 1899 — we are already 

 certain that at least 

 five natural enemies, 

 and probably more, 

 are at work in deci- 

 mating its numbers. 



Exorista pyste Walk, 

 (fig. G), a tachina fly, 

 has been repeatedly 

 reared from the cater- 

 pillar of Hellula undalis from July 27 to as late as October 27. 



Limneriwm tibiator Cress., a very abundant parasite reared with 

 this species, is an ichneumonid. It was reared from the latter part 

 of October until the last week of December. It has not been posi- 

 tively ascertained to prey upon this larva, as it is a well-known enemy 

 of the diamond-backed moth (Plutella cruciferarum Curt.), which 

 was also present in smaller numbers, but as it is also known to attack 

 the cabbage looper (Autographa brassicce Eiley) and Mineola indi- 

 ginella, it seems probable that it is in reality an enemy of this web- 

 worm. 



- Plagiprospherysa sp., a tachinid fly parasite, was reared June 12 

 ano! 17, 1908 ; from its host from Brownsville, Tex. The identifica- 

 tion was made by Mr. C. H. T. Townsend. 



Two other hymenopterous parasites of this webworm, reared in 

 1899, were identified by the late Dr. William H. Ashmead as Meteorus 

 vulgaris Cress, and Temelucha (Porizon) macer Cress., female. The 



Pig. 6. — Exorista pyste, a parasite of the imported cabbage 

 webworm (after Titus). 



