AN ECONOMIC STUDY OF NASONIA BREVICORNIS. 261 



wool or other portions of the carcase, and thus they are more easily found than the 

 other species, all of which generally crawl a considerable distance from the carcase 

 and scatter. Where the pupae of these species have been taken while radiating 

 away from carcases, during February to April and during August to October or even 

 into November, they have often been found heavily parasitised by Nasonia 

 brevicornis. 



In the laboratory, it has been found that the pupae of Anastellorhina augur, Pollenia 

 stygia, Lucilia sericata, and, when obtainable, Calliphora erythrocephala and Sarcophaga 

 aurifrons (i.e., the " smooth " pupae) are attacked by the wasps before the pupae 

 of Pycnosoma rufifacies. This is probably due to the shell of the pupa being thinner 

 in the former five species than in the latter and thus more easily perforated. 



No definite reason can yet be assigned to the apparent distaste of the wasps for 

 the pupae of Ophyra nigra and Pycnosoma varipes in the laboratory. In the field 

 the pupae of the latter species are practically always found to be parasitised. 



The actions of the female wasp when placed with the pupae are very interesting. 

 She first crawls over and over them, her body and antennae twitching constantly. 

 She continually touches the pupae with her antennae, as if seeking for the thinnest 

 part of the shell to puncture. When she has finally decided on the spot to be 

 punctured, the tip of the body is curved downwards and the point of the ovipositor 

 is inserted. The apex of the abdomen is then brought back almost to its normal 

 position, and by so doing the whole length of the ovipositor is exposed, its normal 

 position being in a groove along the ventral plates of the abdomen. From this time 

 the body, except for a slight twitching, remains practically motionless, although 

 the antennae are waving continuously. The ovipositor is gradually inserted, 

 apparently by an upward and downward movement of the styles within the sheath. 

 When fully inserted it remains in that position for perhaps a minute, when it is with- 

 drawn about half its length and is again pushed in. This may occur several times, 

 until at last the whole ovipositor is withdrawn and springs back to its normal position. 



After the ovipositor is withdrawn a small globule of liquid is observed where the 

 puncture had been made. The liquid is either a fluid resembling in its nature a 

 synovial fluid, or else it had been acting as a lubricant for the styles ; the former 

 is the more probable. The female almost immediately turns round and sucks up 

 this liquid and after this there is practically no visible sign of the pupa having been 

 perforated, until the spot dries, when a tiny white dot on the pupal shell is seen where 

 the puncture had been made. 



The time occupied for the whole process of insertion, deposition and withdrawal 

 is very variable. The two extremes which have been noted are 4 minutes and 25 

 minutes. Although the female may attempt to puncture the shell in one spot, she 

 may leave it and make more than one choice of a fresh point before beginning 

 definitely to pierce the pupal shell. 



The position of the body during the process of oviposition is characteristic, being 

 arched from the head to the tip of the abdomen with the ovipositor projecting straight 

 down from the mid-ventral surface of the abdomen. 



In considering the economic value of these parasites when bred in centres for 

 distribution, the length of time they live under certain conditions becomes a most 



