HABITS OF TWO PARASITES OF BLOW-FLIES. 



239 



soil, which was aided by the delay in removing the contents. 

 Whereas the figures for (8), (9), and (10) do bear on tlie subject ; 

 they are as follows : — 



(8) 69 Braconid lined puparia, with dead Chalcid larvae. 



(9) 15 ,, ,, with active* Chalcid larv?e. 

 (10) 23 ,, ,, with some dead Chalcid ima- 

 gines and larvae. 



The outstanding point in this instance of super-parasitism is 

 tliat most of it did not take place in the open, so far as (B) (2) 

 and (C) (8), (9), and (10) are concerned ; it actually took place in 

 the jars in the laboratory, and in proof of this postulation, the 

 puparia could not have been lined by the full-grown larvse 

 by 14th August, or the adults would have emerged before the 

 3rd September, and further super-parasitized Braconids would 

 have been in the larval stage if it had taken place in the open, 

 whereas the contrary was the case. 



To conclude : it has been shown in experiments Nos. 1 and 2 

 that under certain circumstances Xasonia is capable of super- 

 parasitizing a Braconid larva within its lined puparium ; and in 

 experiments Nos. 3 and 4 that blow-fly larvae attacked by the 

 Braconid are stimulated to escape and pupate, and that the 

 majority of them — 76 per cent. — reached 2 inches and more 

 })elow the surface of the soil; and in experiment No. 5 was 

 unable to bui-row to the depths reached l)y the majority, 93 per 

 cent, of the unparasitized blow-fly larvie; and in experiment No. 7 

 definitel}^ failed to reach any one of 93 puparia 2 inches under 

 the surface, which is consistent with their behaviour in the field. 



And, it must be pointed out, that in each instance of super- 

 parasitism reported by Graham-Smith (1 and 4) it appears that the 

 puparia — subsequently ascertained to contain the Braconid 

 primarily — were collected and moved from a "sun" tin to a 

 " shade " tin or vice versa ; and in the case reporter! by the 

 writer, emerging Rasonia remained in the jars containing 

 Braconid parasitized puparia., which were no doubt dislodged by 

 the frequent handling of the jars when releasing Bi-aconids. So 

 that in none of these instances were the conditions even 

 appi'oach ing n at u ra 1 . 



It therefore appears that if super-parasitism takes place in 

 nature, it is not very frequent and then only accidental, and that 

 where it does take place in a puparium of a full-grown blow-fly 

 larva which has been reinforced by a noimal Braconid lining, 

 it is doubtful whether the small, short, and rectangular mandibles 

 (text-fig. 20, a, c) of Nasonia will enable it to escape ; whilst 

 in the case of the female Alelittohia acasta, this is aided by the 

 distinctly acute mandible (text-fig. 20, d) with its one large outer 

 tooth. 



* A few of these were found singly in tlie puparia, and are the largest Wasonia 

 larvae seen by the writer. 



