U2 



SOME OBSERVATIONS ON THE LIFE-HISTORY 

 AND BIONOMICS OF THE KNAPWEED GALL- 

 FLY UROPHORA SOLSTITIALIS LINN. 



By J. T. WADSWORTH, 



Research Assistant, Department of Agricultural Entomology, 

 Universit)/ of Manchester. 



(With Plates XI and XH and 1 Text-figure.) 

 CONTENTS. 



PAGE 



Introduction .......... 142 



Description of tly and cla.ssitication ....... 143 



Geographical distribution ......... 145 



Historical 146 



Food-plants . . 147 



Life-liistory, description of ovipositor, and method of oviposition . 148 



Descriptions of ova, larvae, and pupae 152 



Effects of larvae on production of seeds iu galled flower-heads of 



Cenlaurca nigra L UiO 



Parasites I(i3 



Remarks on gall-formation, and on otlier inhabitants of the flower- 

 heads 164 



Summary ............ 165 



Bibliography ..... ..... 166 



Explanation of ]ilates ......... 168 



Introduction. 



In September 1911, whilst collecting seeds of wild plants at Prestatyn, 

 North Wales, I found galls in many of the flower-heads of the small 

 knapweed, Centaurea nigra L., and these on further examination were 

 found to contain dipterous larvae. 



On counting the seeds contained in a few of the galled flower-heads, 

 and comparing the numbers obtained with the numbers present in 

 ungalled heads, it was seen that considerably fewer seeds were present 

 in the former than in the latter It therefore seemed probable that 



