CHALCID PARASITES OF AUSTRALIAN SHEEP MAGGOT-FLIES. 117 



become heavily infested with these two species, ^^^len the 

 maggots had begun to pupate the box was closed by a '" wasp- 

 proof " gauze, and 250 Nasonias liberated in the box. The 

 Avasps could perhaps scarcely have had a better opportunity 

 for demonstrating their action on pupae buried in the soil, 

 as well as on recently pupated Pycnosoma pupae. As stated 

 above, about a hundred pupae were found beneath the sheep's 

 head, but the result of the experiment showed that several 

 thousand had entered the soil. Pycnosomas hatched in due 

 course in immense numbers . Thirteen days later twelve Nasonias 

 hatched, probably all from one unfortunate pupa ! Here, under 

 the best conchtions, except that they were in captivity (which 

 does not seem to make much difference Avith Nasonia), the 

 wasps were helpless in the face of a reduced pupal jDeriod on 

 the part of their host-fly. It is at least possible that these 

 facts will account for the field observations above quoted. 



If these laboratory experiments can be confirmed in the 

 field, it is evident that little can be hoped from such wasps as 

 oviposit in pupae. Parasites which attack the larvae shoukl 

 be much more useful, since they can obtain access to all the 

 individuals that the former class can, as Avell as man}' that 

 the former cannot. To tliis grovxji belong Chalcis spp. and 

 A ustralencyrtus giravlti. 1'he former can probably be dismissed 

 on account of their rarity, though of course they might 

 be bred up in the laboratory. The latter is more hopeful, as 

 it appears to be fairly common in Brisbane and breeds very 

 easily, but has, unfortunately, a rather long developmental 

 period. The first factor, namely, access to its host, is very 

 favourable ; of the others, hoAvever, nothing is known, and it 

 might turn out quite useless in the field. We hoi)e to distribute 

 a large number later in the year in the ho])e that this Encyrtid 

 lua}^ be of some use. 



To this latter group of maggot attackers belongs also an 

 English Braconid species, Alf/sia mandiirator. This has all 

 the advantages possessed by the above-mentioned maggot- 

 parasitizing wasps, and has also the additional qualification of 

 lajdng a very large number of eggt, and distnbuting them 

 among an equal number of maggots. A A\'asp living under 

 Enghsh conditions might be unable to exist in the Australian 

 climate ; but, on the other hand, it might be stimulated to 

 greater activit)^ and it is certainly a parasite well worth 



