Andricus pilosus. 51 



among the anthers on the catkins either singly or 

 several together. (Fig. 10^.) In order to rear the flies, 

 the galls should be gathered in the end of May shortly 

 before they are mature, and the flies are then obtained 

 about the beginning or middle of June. 



Fly. 1-5 mm. long; black; thorax smooth, slightly 

 shining, scutellum rugose ; abdomen uniformly black, 

 shining; legs from the coxae to the lower third of the 

 femora uniformly dark, the remainder yellowish-testa- 

 ceous ; antennae yellowish, the apices fuscous. The 

 male has the same colouring but the antennae are almost 

 wholly dark. 



Experimental breeding. I made a series of experi- 

 ments with this species in June, 1878, both indoors and 

 out. In some cases I brought the fly straight to the 

 oak sapling, and in others I tied the gall upon the 

 sapling shortly before the escape of the fly. The 

 flies seek by preference the tenderest axillary buds 

 which they begin to prick. When they have selected 

 a suitable bud they poise themselves on its summit and 

 bore the ovipositor obliquely from the surface into the 

 centre of the bud. They lay only one Qgg in each bud, 

 and this invariably occupies from twenty to thirty 

 minutes. While ovipositing the flies are so indifferent 

 to interruption, that it is possible to cut off the twig 

 which they are piercing, and place it under the micro- 

 scope for better observation. As soon as one tgg is 

 laid they immediately seek out a new bud. The average 

 duration of life in this species is about eight days. 



In my experiments in June, 1878, I marked in all 

 twenty-six buds as having been pricked, sixteen indoors 



E 2 



