366 Frit Fly (Oscinis Frit) in Winter Wheat 



No flies hatched out from these pots. An examination of the attacked 

 plants showed that some of the larvae died before pupation. The single 

 pupa which was found was parasitised. 



Of the cases of winter wheat attacked by "frit fly" which I have 

 examined during the last few years, nearly all have been after a ley 

 containing one of the rye grasses ploughed up during the autumn. 



On a farm in Norfolk only one field of wheat after rye grass had 

 escaped. This was ploughed up in the middle of August, whereas the 

 fields which were attacked were ploughed up much later. 



In Cambridgeshire I found a piece of wheat slightly attacked, follow- 

 ing a crop of turnips, but in this case the land was very foul with couch 

 (Agropyrum repens) and other grass weeds, so that it is quite probable 

 that the eggs were laid on these. 



The only other exception was after a crop of white clover, where it 

 is probable that grasses were present with the clover, although not sown. 



I have never seen any appreciable reduction in crop from an attack 

 after potatoes, beans, corn or fallow, but it seems probable that if after 

 either of these the land was covered with grass weeds during the early 

 autumn, the wheat following might be attacked. I have often seen 

 wheat after the above crops free from attacks when neighbouring fields 

 were attacked. 



The damage done by the frit maggot seems to be more on a loose 

 tilth than on a compact tilth. In the former case a larger percentage 

 of plants die, probably because they do not tiller so quickly as on firmer 

 soils. Fields in good condition suffer less than those in poor heart pro- 

 bably for a similar reason. 



These experiments and observations prove that the frit fly larvae 

 present in the rye grasses are capable of migrating to and damaging 

 wheat plants after the grass is ploughed in. 



They also show that an attack of frit fly on winter wheat following 

 rye grass may be avoided by bastard fallowing. Wheat after a bastard 

 fallow, however, is very liable to a bad attack of wheat bulb fly 

 (Lepiohylemyia coarctata), although in the above experiments this pest 

 did very little damage after this method of procedure. 



