HABITS OF TWO PARASITES OF BLOW-FLIES. 



197 



Numbers of the parasite were emerging from the jars at this 

 time, and a lar^^e cac«-e was bronoht into use to contain them. As 

 it was desirable to obtain as man}^ adults as possible, a search was 

 made at the Society's Gardens at the spot where the original 

 material was found, and a further suppl}" of puparia obtained. 

 Whilst sorting out this material preparatory^ to putting the intact 

 puparia into jars, a number of Chalcids w^ere observed crawling 

 about on the soil. Most of these were captured. A closer scrutiny 

 of the puparia disclosed minute holes in several and Chalcids 

 emerging from some of them ; it was also noticed that a few 

 puparia showed that Braconids had emerged from them. In view 

 of the appearance of this Chalcid, each puparium — they were 

 of a CalUphora species and presumably erythrocephala, the same 

 species as the flies — ^was placed in a separate tube. Botli para- 

 ,sites continued to emerge from this material daily for a period of 

 twelve days. 



As no Chalcids appeared from the original material, which had 

 been in the jars for nearly a month, it was evident that they 

 had carried out their attack after the original material had been 

 removed ; and as this consisted entirely of puparia, it seemed 

 reasonable to assume that this Chalcid parasitized the pupal 

 stage. This supposition proved correct, and will be referred to 

 later. 



A constant supply of blow-fl}^ material for parasitization was 

 maintained by putting small receptacles containing meat out in 

 tl>e open and placing it under control as soon as eggs had been 

 deposited on it. No opportunity occurred at this time to obtain 

 meat blown by flies of definite species under control; but with 

 t!iis object in view, small quantities of the larvae from eacli lot of 

 blovvn material were segregated and allowed to develop into 

 adults, Ts^hen their species wore determined, and they were then 

 placed under control in separate cages. 



In the hope that the Braconid was still about, and in order to 

 obtain large numbers of them, receptacles containing soil and 

 meat were put out in the vicinity of the spot from which the 

 original material was obtained ; this, Miss Cheesman kindly 

 undertook to do, and the receptacles w^ere left in the open until 

 the blow-fly larva3 had commenced pupation, when the material 

 was removed to the laboratory to be bi-ed out. It was at once 

 observed that the large parasite was still about. It was seen 

 to come to the receptacles and to attack the larvse. Whilst 

 this was being done, Prof. Lefroy put receptacles out at Heston 

 to see if the parasites could be obtained in this locality. Only 

 the Braconid parasite appeared from the latter place. 



All lots of material obtained from Ilegent's Park and Heston 

 were bred out to observe if any parasites other than the Braconid 

 and Chalcid made their appearance : none did. 



By the end of August large numbers of the parasites were in 

 the cages in the laboratories and extensive bi-eeding operations 

 in progress, and every effort was made to maintain a constant 



14* 



