HYMENOPTERA OAK GALLS. 



157 



far as hitherto ascertained, are a rule without any exception. Yet 

 another point is noticeable viz., that galls appear on certain levels, 

 certain zones of height ; and here we find the apterous flies, in order 

 to reproduce the next generation, have reached the highest zone. 



There is a special entomological interest attached to the oak-apple 

 gall, inasmuch as the list of parasites reared and given by Cameron 

 is quite a little study in itself. The interest is intensified on account 

 of various species appearing throughout the whole year. 



LlORHIZA RENUM (Htg.) 



This is a kidney-shaped gall, as the name implies (fig. 155). It is 

 not very common, but when found is generally abundant on the under 



side of the leaves, and 

 arranged in rows attached 

 to the veins. It is found 

 in September and October, 

 but though I found it sev- 

 eral consecutive years in a 

 Cheshire lane, I yet failed 

 to rear a single fly, 

 which is described as wing- 

 less, and of a brownish-red 

 colour. 



By experimental breed- 

 ing Adler found the fly 

 alternated with Trigon- 



ASPIS MEGAPTERA (criist- 



alis), which is found on 

 adventitious buds on old 

 oak stems near the roots. 

 The gall is about the size 

 of a large pea, of a beauti- 

 ful pink colour, soft and 

 succulent. This gall may be first observed towards the latter end of 

 April, and by the middle of May we find it fully matured, and the 

 insects hatching out. It is very generally distributed throughout the 

 country, but is not always equally abundant every year. Thus in 

 1893 it was very common, but comparatively rare in 1894 and in 



Fig. 155. Galls o/Biorhiza renum (kidney gall). 



