HABITS OF TWO PARASITES OF BLOW-FLlES. 



231 



of a fly-nymph for evidence of the existence of tlie Braconid of 

 which the chitinized liead-capsule of the first in star or mandibles 

 of the second would be the sole initial evidence of its existence, 

 would require time, which the writer at that time could not 

 spare. 



Later — in October — a reference was found to this subject, 

 Graham-Smith (1) on pp. 532-4 and on p. 537, in which another 

 Ohalcid, Melittohia acasta Wlk. (9), is definitely stated to act as a 

 hyper-parasite* on A. mandiicator^ and a passing reference to 

 N. hrevicornis occurs and to tlie existence of numbers of then 

 undetermined Ohalcid larvae in Braconid-lined puparia. Again, 

 in November, further reference (Graham-8mith) (4) was found to 

 this subject, and this time referring to the presence of JS^. hrevi- 

 cornis reared from pupaiia with tlie silk lining of A . manducator. 

 This observer states : — " Puparia collected in the autumn of 1916 

 and kept outside yielded in May 1917 38 males and 36 females. 

 Some of these autumn pu-paria had been parasitized by ^4. mandu- 

 cator Some of these autumn puparia i-eniained intact, and 



were dissected in March 1918. Of these, 28 were found to 

 contain living Ohalcid larvfe, and were kept in tubes in a warm 

 room. Nineteen of tliese 28 showed infection with A. ma)iducator. 

 Adult iY. hrevicornis, 11 males and 48 females, emerged in May 

 1918, a year and a half after the puparia were collected." 



The writer therefore decided to carry out an investigation into 

 this important matter ; and as the subject is of considerable 

 interest, the various experiments are given in detail. 



To begin with, it might be mentioned that the point previously 

 referred to — i. e., secondai-y parasitism in the early stages of the 

 Braconid larvre— was not investigated, for the reason stated. 



The following two experiments were made to verify the above 

 quoted statement : — 



Experiment No. 1. — A large tube 6 inches x 1 inch was used. 

 Into this was placed — on 25th November — one normal size Calli- 

 phora puparium, in which a small fracture of the pupal case was 

 made so as to disclose the Braconid lining, and therefore denoting 

 the presence of either a full-grown larva,, pro-pupa, or pupa. 

 Three fertilized and lecently-emerged females of N. hrevicornis 

 were then released in the tube, and on the inside of it a small 

 quantity of food was smeared. The tube was kept under occa- 

 sional observation for four days, during which time none of the 

 females were seen to oviposit, but could be seen crawling over 

 the puparium, carrying out the usual critical examination. 

 After 29th November no further observations were made. On 

 17th December — -21 days later — the tube was opened ; the three 

 females were dead, and the puparium was then carefully opened 

 under binoculars. In it was found one a,ctive full-grown Ohalcid 

 larva, two dead and dried-up larvse apparentl}^ nearly full-grown, 

 and two small shrivelled masses of newdy emerged larvse. The 



* There appears to have been nothing else in the tins where this occurred except 

 puparia containing individuals of A. manducator. 



