PARASITE, APHIDIUS TESTACEIPES. 



113 



emerge as an adult after the first movements of the pupa begin, and 

 when ready to issue the pupa expands and contracts the abdomen, 

 moving the feet and antennae until these are freed from their gum- 

 like covering. Upon studying the pupae (fig. 27) 

 closely, we find that the prothorax bears two rows 

 of distinct elevations or tubercles, but we have 

 been unable thus far to ascribe any particular 

 function to them and they disappear with the 

 gum-like covering. The junior author finds that 

 the adult gradually works itself about until it gets 

 in a position with its back to the ventrum of the 

 old aphidid shell, when it cuts a circular hole, as 

 described by Mr. Kelly, and crawls out, always 

 with its head pointing toward the head of the old 

 aphidid. Figure 28 represents an old dead body of 

 a " green bug" after the parasite has issued. 



Fig. 27. — Pupa of 

 Aphidius testaceipes 

 immediately after 

 pupation. Much 

 enlarged. (Origi- 

 nal.) 



FECUNDITY. 



fTTT 



From the prompt manner in which Aphidius, under favorable 

 weather conditions, overcomes Toxoptera it will readily be seen that 



the former must be a very prolific breeder. The 

 average adult female contains from 4 to 450 

 eggs. These eggs are lemon-shaped (see fig. 

 19), very pale, and translucent. 



Messrs. Kelly and Urbahns conducted a 

 number of experiments at Wellington, Kans., 

 in 1908, to determine the number of offspring 

 produced by one individual. They found that 

 one Aphidius would parasitize as many as 206 

 Toxoptera. In their experiments, however, 

 they used only a few more than 200 Toxoptera 

 to each individual. Mr. Parks, at the same 

 place in 1909, conducted 16 experiments, using 

 from 300 to 500 Toxoptera and he had a maxi- 

 mum, in one case, of 301 aphidids parasitized 

 from one individual Aphidius. His minimum 

 was 3; his next highest number was 33, and 

 his next was 44. Of the sixteen, 12 fell below 

 100; his average was 94.6. 



Mr. Parks also conducted experiments at the 

 same time as the above to ascertain what the ef- 

 fects of continuous mating of one male to differ- 

 ent females would have on the offspring. In 

 this experiment 1 male was mated to 12 unfertilized females within a 

 period of two hours, after which each female was placed in a separate 

 cage with about 100 Toxoptera that had not been exposed to Aphidius. 

 26675°— Bull. 110—12 8 



Fig. 28.— Dead "green bugs" 

 (Toxoptera graminum), 

 showing holes from which 

 the matured parasites of 

 A phidius testaceipes emerge. 

 The top figure shows the lid 

 still attached, but pushed 

 back; the bottom figure 

 shows the parasite emerg- 

 ing. Enlarged. (From 

 Webster.) 



