165 



ADDITIONAL HOST PLANTS OF OSCINELLA FRIT, 

 LINN. AMONG GRASSES. 



By NORMAN CUNLIFFE, M.A. (Cantab.), 



Christopher Welch Lecturer in Economic Zoology, University of Oxford. 



The following observations supplement those recently recorded (i) 

 relating to the utilisation of certain grasses as host plants by 0. frit. 

 As, in previous experiments, positive results even with the same species 

 of grass were decidedly irregular, it was concluded that the small scale 

 of pot experiments might be unduly influencing reproduction. These flies 

 are difficult to rear, owing to their sensitiveness to unfavourable environ- 

 mental factors. Therefore in 1920 and 1921 outdoor musHn cages measuring 

 6' X 6' X 4' were given a trial but, although the conditions were apparently 

 more favourable for oviposition they were not ideal, as emergence figures 

 were still small. In addition to determining which grasses 0. frit could 

 utilise as host plants, it was desired to obtain some evidence as to the 

 relative preference for different hosts at different periods of the year. 



Grasses Utilised in Winter. Experiments I to III. 



Briefly the history of the host plants used in the following experi- 

 ments was as follows: the seeds were sown on 23. iii. 20 under protective 

 muslin cages, the plants being cut down to a height of 4 inches on 1. vi. 20, 

 planted out in 9 inch pots (four roots per pot) on 29. vii. 20 and on the 

 same day recut to a height of 4 inches to induce tillering. The pots were 

 sunk to the brim in a shallow pit under one of the large cages, five pots 

 of each species of grass used being distributed as evenly as possible 

 therein. The parent flies, bred from oat grains, were divided into four 

 lots and introduced through each of the four sides of the cage, water 

 and food (in the form of sugar) being present in the cage in abundance. 

 Thus, as far as possible, the effect of sluggishness on the part of the fly 

 was eliminated, and also the separation of the host plants was facilitated 

 when it became necessary to cage them separately for recording emer- 

 gence. The small cages were examined at intervals of three or four days, 

 and the newly emerged flies removed. Owing to the small numbers only 

 the total emergence from each species of host plant over each interval 

 is shown below. 



11—5 



