246 DIPTERA OR TRUE FLIES. 



forming a small black passage in which the gruh turns to a 

 yellowish-brown puparium. From this there appears a second 

 brood of flies, which deposit their ova on various wild grasses, 

 and pass the winter in them. That is the reason why we 

 always find this gout attack most marked round the borders 

 of the fields and along the grassy headlands, and any rough 

 grassy ditch running across the land. Sometimes the plant is 

 sufficiently strong to come out of its sheathing leaves, and then 

 we can detect its presence by some of the grains having gone, 

 and by the black tunnel extending from the ear down to the 

 first node. 



An Ichneumon (OceUnius nig&r) attacks the Gout Fly larva 

 (fig. 140, 4 and 4a), also a small Pteromdlus described by Curtis 

 as P. iiu'rans. 



Prevention and Remedies. — Early sowing is one of the best 

 preventives, and the application of stimulating dressings to the 

 crop so as to carry it along. Mowing down the rough grasses 

 round the headlands, &c., in the winter and burning them will 

 kill numbers, for they are found breeding in such places in the 

 winter and also hibernating as adults there. 



Family OSCINIDJE. 



The Frit Fly (Oscinis fkit). 



Oats are often seriously injured past recovery by a small 

 larva in the centre of the plant. The disease is spoken of 

 as " Botley " or " Potley " Oats. This is the larva of a small 

 black fly, the Frit Fly, which belongs to the family Oscinidiv. 

 We notice this pest by the young crop withering away in 

 June. Generally speaking, the Frit Fly damage can be re- 

 paired if taken in time. Barley is attacked on the Continent 

 as well as oats, but in Britain only the latter suffers. We can 

 early detect its presence by the central leaves here and there 

 turning brown or reddish-yellow, and on examination a small 



