PARASITE, APHIDIUS TESTACEIPES. 115 



during the summer of 1907, while making observations on the life 

 history of the species; hence, a series of experiments was begun in 

 order to learn something definite in regard to it. Seven female 

 Aphidius were selected, just as they issued from their cocoons (being 

 therefore unfertilized), and placed in separate cages with 30 to 40 

 Toxoptera not previously exposed to parasite attack. All of the 

 parasites began ovipositing at once. After one of the females had 

 apparently parasitized all of the aphidids in her cage she was mated 

 and placed in a second cage with a number of Toxoptera as before. 

 All the offspring from unmated females were males, but the offspring 

 from the single female, after she had mated, comprised 22 females 

 and 4 males. 



Messrs. Kelly and Urbahns elucidated this phenomenon more fully 

 during the summer of 1908 at Wellington, Kans. 1 These experi- 

 ments were conducted as follows : 



Starting with a mated female, the females from among her off- 

 spring were isolated, even before emergence. On their appearance 

 they were given Toxoptera not previously exposed to parasitic attack. 

 The few females from among this second generation were again 

 isolated in the same manner, the females in all cases being kept 

 unmated. Nearly 100 experiments were conducted in this manner, 

 but only 48 gave results. The offspring of 44 out of the 48 isolated 

 were, all of them, males. Of the 4 remaining females, the offspring 

 of 3 were as follows: 70 males antl 3 females; 101 males and 6 females; 

 67 males and 1 female. In the case of the remaining female, some 

 uncertainty exists as to whether she had been fertilized or not, and, 

 for this reason, a census of her offspring is not here included. 



Of the three exceptional cases the offspring from one female were 

 not bred any further; from a second, the offspring became all males 

 in the second generation; the offspring from the third female produced 

 two females in the second generation, all finally becoming males in 

 the third generation. 



In this manner it will be seen that Messrs. Kelly and Urbahns were 

 able to rear a limited number of females parthenogenetically to the 

 tlrird generation. Beyond this all of the offspring were males. While 

 the conditions under which these experiments were conducted would 

 not obtain under ordinary field conditions where the infestation was 

 great, it could very easily occur where there are very few aphidids 

 present. This apparently abnormal feature, then, would greatly 

 assist the species in tiding over periods of scarcity of plant-lice. 



HOSTS OF APHIDIUS TESTACEIPES. 



Since we were able to find Aphidius testaceipes over almost the entire 

 United States, it seemed clear to us that it must have hosts other than 

 Toxoptera graminum. Accordingly Messrs. Kelly and Urbahns con- 



i Ann. Ent. Soc. Amer., vol. 2, No. 2, 1909, pp. 67-87. 



