134 



The extent to which a parasitic insect can control its host depends on 

 various factors. The most important is the readiness with which the 

 parasite can gain access to the host, its usefulness depending on the 

 ratio of hosts available for attack to those which are inaccessible. A 

 second factor is the relative rates of breeding of both parasite and host. 

 Others are the presence of food for the adult stages of the parasite, the 

 suitability of environment as regards temperature and humidity, and 

 the presence of hyperparasites. The first two factors were investigated, 

 but the results proved unfavourable, mdicating that unless the 

 behaviour of the Chalcids under field conditions in sheep country are 

 different from those observed in Brisbane, they are of little importance 

 as controlhng agents. 



The parasites, Dirhinus sarcophagac, Frogg., Pachycrepoidens 

 dubiiis, Ashm., Hemilexomyia abnipia, Dodd, Chalcis dipterophaga, 

 Gir. & Dodd, C. calliphorae, Frogg., Paraspilomicnis froggatti, Johnst. 

 & Tiegs, and Spalangia miiscidanmi, Richardson, are too scarce to be 

 of economic importance. 



Experiments were undertaken in Brisbane to test the economic im- 

 portance of Nasonia brevicornis, Ashm. From these it was seen that 

 the majority of sheep-maggot flies apparently pupate in places where the 

 Chalcids cannot touch them, only a small number, about 4-37 per cent., 

 which pupate on the surface, becoming parasitised. The flies breed 

 much faster than the Chalcids, a single female Nasonia parasitising 

 on an average about 20 pupae, while a single female blow-fly can deposit 

 about 250 eggs. During the hot season blow-fly pupae, on account of 

 their accelerated development, are more immune from eft'ective attacks 

 by such Chalcids as parasitise the pupal stage. The authors are 

 therefore forced to regard this Chalcid as a greatly overestimated factor 

 in the control of blow-flies. 



The hfe-history of Anstralencyrtus giraiiUi, Johnston & Tiegs, has 

 .already been noticed [R.A.E., B, x, 1]. It is abundant in Brisbane 

 during October and November, but diminishes as the summer advances, 

 ■when N. brevicornis becomes more plentiful. Its chief advantage is 

 that it attacks the larval stage ; the disadvantages connected with it 

 are its long developmental period and periodic appearance, which might 

 be remedied by means of laboratory supplies. It seems worthy of 

 trial imder field conditions in Western Queensland. Stenosterys 

 ftdvoventralis [R.A.E., B, x, 56] appears to be a synonym of this 

 species. 



Careful observations on the relation of Alysia manducator, Panz., 

 to useful flies are necessary before it is utilised as a parasite of blow-fly 

 larvae [R.A.E., B, x, 1, 55]. 



RosENBERGER (G.). Studicii ubei die in- und extrazellular liegenden 

 Bickettsien. [Studies on the intra- and extra-cellular Rickettsia.'] — 

 Arch. Schiffs- u. Trop.-Hyg., Leipsic, xxvi, no. 4, April 1922, 

 pp. 112-119. 



Lice free from Rickettsia proivazeki have been found to be infested 

 by another species, R. rocha-limae, Weigh 



Crumb (S. E.). A Mosquito Attractant. — Science, Garrison, N.Y., 

 Iv, no. 1426, 28th April 1922, pp. 446-447. 

 During 1919 a number of attractants were tested in order to ascertain 

 their possible value in mosquito control. Crude mixtures of the com 

 ponents of blood and of perspiration apparently produced faint and 



