238 



MR. A. M. ALTSOX ON THE LIFE- HISTORY AND 



(7) Unlined pnparia, with active Chalcicl larvae. (These had, 



superficially, Hy-remains.) 



(8) Braconid lined pnparia, with dead Chalcid larv?e. (The 



Bracoiiids were in all stages, pup?e predominating.) 



(9) Braconid lined pnparia, with active Chalcid larvfe. (These 



Braconids were in all stages, pupae predominating.) 

 (10) Braconid lined pnparia, with some dead Chalcid imagines 

 and larvae. (These consisted, with one exception, of at 

 least one male.) 



The examination of these puparia showed that where super- 

 parasitism had taken place, with the exception of a very few 

 instances — the numbers were not noted, — the puparium concerned 

 was a very small one, about the size of M. domestica, and con- 

 sequently, in the case of a blow-fly, a puparium with an exception- 

 ally thin integument. And, further, that the attack of the 

 Chalcid larvae had taken place in the abdomen of the Braconid 

 where this was an advanced pupa, the only pa it where soft 

 integument exists, due to the distention of the abdomen 

 consequent upon the presence of the meconium (text- fig. 7) : it, 

 therefore, seems conclusive that a Nasonia female is able to 

 distinguish between a hard sui'face and one yielding to pressure, 

 by means of the apex of her ovipositor. It is worthy to note 

 that Nasonia appeared to be most effective when the Braconid 

 was a pupa — that is to say, in the identical stage of development 

 to that of its normal dipterous hosts. 



The numbers under the heading (B) were (1) 33 pupa.ria, with 

 Chalcid exit-holes and unlined by the Braconid, presumed pri- 

 mary parasitism ; and (2) 17 with Chalcid exit-holes and definite 

 super-parasitism. In each instance the puparium had been lined 

 by the Braconid. A feature of these 17 puparia was the position 

 of the exit-hole : in 3 it was made in or about the middle of the 

 puparium, in 6 at the apex of the anterior end, and in 8 a.t the 

 apex of the posterior en.d. In only one instance had two efforts 

 been made to escape. This occurred in one of the 3 ; a small some- 

 what elongated aperture had been made in a position diametrically 

 opposed to the exit hole used. A point of grea,t interest in the 

 writer's opinion, with regard to the position of the exit-hole in 

 the above, is that in 6 the Chalcid got out at a point where the 

 Braconid lining is weakest — that is, where it is run over the pro- 

 truding chitinized mouth-parts of the late blow-fly larva ; and 

 in 8 the Chalcid got out at the next weakest point — that is, 

 where the lining is run over the blow-fly larva's posterior 

 spiracles. 



The figures under heading (C) are not given in detail ; those 

 for sub-headings (1) to (7) do not materially bear on the subject of 

 the investigation, but for 1 and 2 they were very high, and mainly 

 due, in the writer's opinion, to the unshaded position of the glass 

 receptacle and consequent evaporation of any moisture in the 



