532 



HYMENOPTERA 



CHAP. 



shown, is possibly a Chalcid of the genus Monodontoynerus, or 

 may be Callimome hedeguaris. It is clear that, as we cannot 

 ascertain what is inside a gall without opening it, and thereby 

 killing the tenants, it is a most difficult matter to identify the 

 larvae ; the only safe method is that of observation of the act of 

 oviposition ; this may be supplemented by rearing the flies from 

 galls, so as to ascertain what variety of flies are associated with 

 each kind of gall. This last point has been well attended to ; 

 but the number of cases in which oviposition of inquiline gall- 

 flies in the galls formed by the Psenides has been ascertained by 

 direct observation is still very small ; they are, however, sufficient 

 to show that the inquilines deposit their eggs only after the 

 galls are formed. 



Fig. 350. Larvae in- 

 habiting bedeguar 

 gall at Cambridge, 

 1, Rhodites rosae 

 in cell ; 2 and 3, 

 larvae of inqui- 

 lines ; 4, larva of 

 a parasitic Hymen- 

 opteron. 



Bassett recorded the first case of the kind in connexion with a 

 North American species, Cynips {Ceroptres) quercus-arhos Fitch. 

 He says : " On the first of June galls on Quercus ilicifolia had 

 reached their full size, but were still tender, quite like the 

 young shoots of which they formed part. Examining them on 

 that day, I discovered on them two gall-flies, which I succeeded 

 in taking. They were females, and the ovipositor of each was 

 inserted into the gall so deeply that they could not readily free 

 themselves, and they were removed by force." 



The great resemblance of the inquiline gall-fly to the fly that 

 makes the gall both dwell in, has been several times noticed by 

 Osten Sacken, who says " one of the most curious circumstances 

 connected with the history of two North American blackberry 

 galls is, that besides the Diastroplius, which apparently is the 

 genuine originator of the gall, they produce another gall-fly, no 

 doubt an inquiline, belonging to the genus Aulax, and showing 

 the most striking resemblance in size, colouring, and sculpture to 

 the Diastro'phus, their companion. The one is the very counterpart 



