October, '11) GAHAN: NOTES ON PARASITES 425 



site was present in small numbers, but it was not until May 25 that 

 evidence was found of the advent of a new generation of the parasite. 

 On this date several swollen bodies of lice were found and from two of 

 these the parasites had already emerged. Maj^ 27 I was able to collect 

 a considerable number of pupating parasites, and by the thirtieth, the 

 dead, swollen bodies of the parasitized lice were very abundant on 

 the leaves, stems and heads of both rye and oats. It was also notice- 

 able that many of the large living aphides were of a very much darker 

 color than normal and upon dissection these were invariably found to 

 contain the nearly full grown larva of the parasite. It was also noted 

 that these dark colored individuals were rarely surrounded with colonies 

 of newly born aphides, as was the case with normal specimens, thus 

 showing that reproduction had been stopped some time before the 

 death of the louse, a fact having considerable bearing on the efficiency 

 of the parasite, as previously pointed out by Professor Webster in his 

 account of the Lysiphlehus parasite of Toxoptera graminum. 



An attempt to determine the length of the life cycle of the parasite 

 was unsuccessful, owing to the fact that it was carried out in an ordinary 

 glass-covered insectary, the temperature of which proved to be too 

 high for their development. Observations, however, warrant the 

 belief that the normal development in June covers a period of from 

 fourteen to sixteen days. The period from the death of the host 

 until emergence of the parasite is usually about five days. 



The parasites continued to increase in abundance until the grain 

 was cut, by which time the majority of the aphides in the fields were 

 parasitized. There can be but little doubt that had it not been for 

 the presence of this parasite, the damage to the grain on the Experi- 

 ment Station farm would have been severe in both seasons. As it 

 was, little damage was done. -_ 



NOTES ON THE LIFE HISTORY OF THE TICK PARASITE 



Hunter ellus hookeri Howard ^ 

 By H. P. Wood, Bureau of Entomology 



Introduction 



Only two hymenopterous parasites of the Ixodoidea or ticks have 

 ever been discovered. About one of these (Ixodiphagus texanus How.) 

 almost nothing is known. The other, belonging to the same tribe of 

 encyrtine chalcidids, Hunterellus hookeri Howard, is of peculiar 



Published by permission of the Chief of tlie Bureau of Entomology 



