HYMENOFTERA OAK GALLS. 147 



is to be sought for in Spathegaster aprilinus," and this conjecture 

 has since proved to be correct. 



5a. Spathegaster aprilinus (Gir.) 



The galls of this species are formed in buds, but the formation is 

 so obscure as to be frequently overlooked. In fact, we should con- 

 sider them abortive buds, and the best way to find them is to look 

 for abortive buds just after the leaves develop. It should be noted 

 that undeveloped buds, frequently found in oaks after the early 

 flushing of the leaves, are due to the attacks of this species. In 

 order to hatch those galls it is best to collect them about the end 

 of April or beginning of May. 



The fly is described by Adler as follows : " Length 2.5 mm., 

 black thorax, somewhat shining ; scutellum wrinkled, abdomen shin- 

 ing, antennas black, legs dark-yellow, coxa? and basal half of the 

 femora blackish. Males and females similar in colouring." 



'O' 



Genus Aphilothrix. 



The second group, according to Adler, having alternate generations, 

 is the Aphilothrix- Andricus Group. The genus Aphilothrix includes 

 a large number of gall-flies found 

 only in the female sex. The genus 

 Andricus yields the sexual form. 



6. Aphilothrix radicis (Fabr.) 



This gall (fig. 140) is found on 

 the lower part of the trunk, or 



lUSt 011 the horizontal portion of Fig. 140.- GWJ o/ Aphilothrix radicis. In 



l section to show chambers. 



the root above ground. At first it 



appears as a large softish mass, but ultimately it becomes quite hard 

 in the centre, and a section made in mid-winter will reveal a many- 

 chambered gall with a fully developed fly in each chamber. They 

 hatch out about the latter end of April. 



The fly is reddish-brown, with longitudinal stripes on the thorax. 

 The abdomen is somewhat dark, and the thorax is covered with a fine 

 silky pubescence. The antennas are dark-brown. Length from 5 to 



