242 



MR. A. M. ALTSON OX THE LIFE-HISTOHY AND 



place, but where artificially propagated, this would be a great 

 advantage in ensuriiig a continual overlapping of generations, 

 and so obtain the benefit of its activity throughout its season. 



On the other hand, the females only of N. hrevicornis are 

 capable of flight, and which — so far as has been observed — 

 consists of long jumps of 6 feet or so at a time, its commonest 

 method of progression being to crawl. The males are semi- 

 apterous and quite incapable of flight, and although they are of a 

 domesticated " temperament," remaining in the vicinity whence 

 they emei'ge, thoy are very liable to ovei-look their natural 

 functions whilst endeavouring to obtain mastery over rivals, and 

 consequently the unfertilized females would, parthenogeuetically, 

 produce a colony of males, possibly isolated and incapable of 

 finding mates or doing any damage to blow-flies. For these 

 reasons, it seems obvious that Nasonia cannot prove to be a 

 decisive factor in blow-fly control unless they are constantly 

 distributed in large numbers over small areas. Whereas, if they 

 were artificially propagated and distributed on these constant 

 refuse-heaps foinid in and around populous areas, and near 

 dung-heaps in town and countiy stables — whence to be farther, 

 unwittingly, distributed, — Nasonia would, on account of its 

 semi-social and " domesticated habits, piove a most important 

 factor in the control of "The Common House-or Typhoid-fly and 

 its allies," which are constantl}^ breeding in such stercoraceous 

 places and where host puparia w^ould l)e within crawling distance 

 of the Chalcid. 



Summary. 



(1) The breeding operations and accumulation of supplies of 

 Alysia maiulvcator Panz. and Nasonia hrevicornis Ashm. com- 

 menced in July and ceased in December 1919. 



(2) Alysia manducator oviposits in the larvae of seveial carrion- 

 feeding Diptera. Only one parasite emerges from each host 

 puparia. Over-parasitism kills the larva. The mean average of 

 the life-cycle is 52 days, and as short as 25. Both sexes are 

 capable of sustained flight, and lived over a month in captivity. 

 Average percentage of parasitism over three years was 43 per 

 cent., observed by Graham-Smith (4). Average contents of 

 ovaries 366 eggs for 12 females. 



(3) Nasonia hrevicornis oviposits in the puparia of several 

 species of stercoral and carrion-feeding Dipterous larvae. From 

 one to 62 individuals have been found in single puparia parasi- 

 tized in captivity. The length of the life-cycle ranges from 11 to 

 22^ days in different countries. Only the female can fly, and then 

 onfy very short distances, and can live, whilst ovipositing, from 

 4 to 6 weeks,but for a considerably less period without host puparia. 

 The male remains near the vicinity of emergence, where its life 

 is spent in fighting and mating. Average progeny in the case of 

 five females — observed by Girault & Saunders and McCarthy — 

 was 113 per female, and aflfecting on the average only 16-4 hosts, 



