HABITS OF TWO PARASITES OF BLOW- FLIES. 



215 



in the latter nearly 90 per cent. That the latter figure is a true 

 index of the extent of Biaconid infection in the original stock of 

 pup^e is shown by the fact that 9 per cent, of the pnp?e in the sun 

 tin were not parasitised."' Of two lots of puparia from which — 

 the parasite emerged during 1916, this observer found (4): — 

 ^' At least 25 per cent, of the puparia" from one lot "and 57 per 

 cent, of tliose" from the other "were infected with A. mandu- 

 catory Summarizing his observations on emei'gence of this 

 parasite in 1915-16-17, he says (4):— "Of the 16,028 puparia 

 collected in the autumn of 1914-15-16 from sunny and shady 

 situations 7041 or 43 percent, were infected with A. 7nanducator, 

 while of the 4787 puparia collected during the summer months 

 of 1916-17 only 508 or 10 per cent, were infected." 



From two lots of material collected from Regent's Park on 

 27th July, and where parasitization by " free Braconids occurred 

 under conditions similar to those above, the writer found the 

 percentage of parasitism to be 23*12 per 3ent. and 52'32 per cent, 

 respectively. These lots were both brought in at a time when 

 the larvfe had begun to pupate, they were examined in November, 

 previous to this time emergence had ceased. The figures given 

 are derived from the number of puparia from which A. maiidu- 

 cator had emerged, and from those intact puparia in which dead 

 adults, dead pup?e, and active and dead larva? of the parasite were 

 found, as against the total number of puparia in the leceptacles, 

 including those from which flies had emerged, or failed to 

 emerge, and those containing atrophied fly-nymphs. It would 

 be of interest to know the number of females responsible for 

 these figures. Dead females were always found in the receptacle, 

 but no reliance can be placed on their number. 



In laboratory -bred material, in ten lots, it was found that the 

 percentage of parasitization i-anged from 15*04 per cent, to 48*99 

 per cent., the lattei* figure being due to nin-e females. But the 

 outstanding feature of this examination was, that it took a total 

 of 39 females to reproduce definitely 1306 individuals exclusive 

 of over-parasitized larva? — an average of 33*74 each, or only 

 9*89 per cent, of their average egg-capacity. This result can but 

 be attributed to confinement and to the bad ventilation of the 

 cage, also to the fact that the parasite's sense-organs, which are 

 normally stimulated to bring about the inclination to oviposit, 

 would have been dulled and deadened by the ever-present odour 

 of carrion in the laboratory. Under better caging conditions 

 and when living in an atmosphere unpolluted with the stench of 

 the putrefactive juices of the carrion, better results would 

 certainly be obtained. 



Hihernation. — A. manducator hibernates as a full-grown larv».. 

 This was observed under natui-al conditions by Graham-Smith 

 (1 and 4), and is supported by the condition of the stock material 

 and by the Refrigerating Experiment. 



Attraction to Light. — Artificial light is very attractive, and 

 caused the insects to crowd on that side of the cage nearest to it. 



