no PROCEEDINGS OF THE KOVAL SOCIETY OP (^IJEENSLAND. 



fertilisation actually took place before the wasps had emerged 

 from the fly puparium. If this method alone took place in 

 nature then the only opportunity for true interbreeding 

 instead of inbreeding would occur when two females chanced 

 to parasitize the same maggot. Copulation has been observed 

 to take place immediately after emergence, the act occupying 

 about a quarter cf a minute. 



The Avasp is an exceedingly active little creature, and is 

 easily distinguished from Nasonia by the brown colour of the 

 \inder side, as well as by its much greater activity often mani- 

 fested by leaping movements. It does nov appear to live very 

 well in close captivity, where our method adopted in keeping 

 them has been merely to place them in glass tubes and provide 

 them with a little diluted honey. Under these conditions they 

 began to die on about the third day, and we have not kept 

 them alive longer than seven days. 



B. - THE ECONOMIC SIGNIFICANCE OF THESE 

 CHALCID PARASITES. 



The extent to which a species of parasite is capable of 

 destroying or checking the numbers of its host species depends 

 on numerous factors, all of which must be taken into account, 

 yet which it is often exceedingly difficult to estimate, even 

 roughly. These factors, in the case of the parasites of Aus- 

 tralian sheep-flies, are very complex. 



The most important of these factors is the accessibiUty 

 of the host species to the parasite. If the parasite has relatively 

 little opportunity of access, it cannot do much harm to the 

 species as a whole. It may destroy large numbers of specimens 

 of its host species, but the really important question, from an 

 economic standpoint, is the ratio of the number destroyed to 

 the number not available for attack. The relative importance 

 of this factor will depend, therefore, partly on the habits of 

 the host species and partly on that of the parasite. Unfor- 

 tunately these habits are but scantily known at present. 



A second important factor will be the capacity of the 

 parasite for inhabiting a certain locahty in sufficient numbers. 

 This will depend i:)artly on the presence or absence of necessary 

 food or of enemies, and partly on climatic conditions. 



A third important factor, and one wliich it is impossible to 

 ■estimate in the laboratory, may be stated as follows : — Given 



