A. Roebuck 181 



From this it will be seen that all varieties were attacked. It must be 

 remembered that this table deals with ears only, the individual "blind" 

 spikelets were not counted. Hence the table is no criterion of the actual 

 damage, one variety may have had a few ears attacked severely and 

 another a large number of ears attacked slightly. 



Position of this Attack in the Life Cycle of the Frit Fly. 



In this country entomologists have long recognised three broods — 

 one on grasses, one on the oat stems and another in the oat grains. There 

 has ahvays been a difficulty, if the broods were sharply defined, of the 

 long interval between the tillers dying in spring and the grain being- 

 attacked. This difficulty was emphasised by Ritzema Bos as early as 

 1891. A brood intermediate between the one on the oat stems and the 

 one in the grains has been somewhat uncertain in this country. The 

 association of the name brood with the nature of attack has possibly 

 added somewhat to the uncertainty, but more particularly the apparent 

 overlapping of the broods is a difficulty. 



The following table indicates the position of this attack in the life 

 cycle. It is based on field observations in Shropshire extending over 

 five years, except this particular attack, which is on one year. 



Period of maxiinum 

 Site of pupa Earliest gathered pupa emergence of flies 



Grass stems (Arrhenatherum) March 25th 1st week of May 



Base of oat tillers ... ... May 21st Middle of June 



Panicle inside leaf ... ... June 24th 3rd week of July 



Oat grains ... ... ... July 31st 1st week of September 



The period of maximum emergence is given because both stem attack 

 and this attack causing "blindness" continue until harvest as more 

 tillers are produced and more panicles unfurl. 



This table would seem to supply evidence in the field in this country 

 in support of dates obtained from indoor cultures by Dobrovliansky 

 in Russia during 1915 (vide Collin in Annals of Applied Biology, vol. v, 

 p. 85). 



Conclusion. 



From the abundance of evidence obtained last summer I feel justified 

 in suggesting that there may be three broods of frit flies on the oat crop 

 and that "blindness" is caused by the intermediate one. Probably only 

 a certain percentage of the intermediate brood cause this "blindness" 

 — the remainder entering newly forming tillers. Perhaps the scarcity of 



