1909] 



Toxoptera graminiim and its Parasites 



85 



The celerity with which an invasion of Toxoptera is overcome 

 by Lysiphlehus, is frequently a matter of wonder, as it hardly 

 seems possible that this host alone could be the source of the 

 swarms of individuals that make their 

 appearance after a few warm days have 

 elapsed, in the midst of an unseason- 

 ably cool spring, preceded by a winter 

 abnormall^^ mild. 



In order to determine the origin of 

 these myriads of parasites, Messrs. 

 Kelly and Urbahns began a long series 

 of experiments at Wellington, Kansas, 

 to determine whether there might not 

 be a multiplicity of host species from 

 which greats numbers of Lysiphlehiis 

 would emanate to fall upon and destroy 

 Toxoptera whenever it becomes exces- 

 sively abundant. The entire failure to 

 introduce these parasites in advance of 

 an invasion of this character from the 

 south, as was the case in Kansas in 

 May, 1907, has indicated that such intro- 

 ductions were not possible and that to 

 attempt it was a veritable carrying of 

 coal to Newcastle. 



Female Lysiphlehus from Aphis hrassicce taken from the field 

 w^ere first bred into Toxoptera from which adults were obtained. 



Fig. 10— Dead "green 



bugs," showing hole from 

 which the matured parasite 

 of Lysiphlehus tritici emer- 

 ges. The top figure shows 

 the lid still attached, but 

 pushed back; the bottom 

 figure shown the parasite 

 emerging. Enlarged (ori- 

 ginal.) 



W Fig. 1 1 — a, Larva of Lysiphlehus tritici working its way premature- ^ 

 ly from body of Toxoptera graminum; b, same larva, somewhat further 

 developed; c, same, still more developed. Enlarged (original). 



