SOME OBSERVATIONS ON THE LIFE‐HISTORY AND BIONOMICS OF THE KNAPWEED GALLFLY UROPHORA SOLSTITIALIS LINN

SUMMARY1 A description of Urophora solstitialis L. and an account of its systematic position and geographical distribution are given, together with an abstract of the work of previous observers on this species. 2 A list of its British and continental food‐plants is given; the records of the latter show that on the continent the larvae feed on various species of thistles, and on three species of Centaurea , but not on Centaurea nigra , whereas with the exception of one record of their occurrence on Serratula tinctoria , the larvae in this country are recorded as feeding exclusively on Centaurea nigra.3 The life‐history, ovipositor, and method of oviposition are described, and descriptions and figures of the ova, larvae, and pupae are given. The life‐history is summarised on p. 118. 4 It is shown that owing to the formation of gails induced by larvae of U. solstitialis in the flower‐heads of this weed a reduction in the number of seeds is effected amounting to about 50 per cent, in the heads examined. The gerininative capacity of the seeds produced in these galled heads was also adversely affected. In the germination experiment described 60‐5 per cent, fewer seeds germinated from galled flower‐heads of V. nigra than from ungalled ones. At a moderate estimate the number of seeds rendered non‐effective in galled flower‐heads of C. nigra is placed at f)0 per cent. It is pointed out that Try‐paneids, whose larvae adversely affect the weeds of cultivated land, may be regarded as beneficial. 6 A short account and discussion of the recorded parasites of U. solstitialis is given. 7 Some interesting features observed in the process of gall‐formation are referred to, and a few notes are added on some other insect inhabitants of the flower‐heads of C. nigra.