1921.] 



The Frit Fly. 



27a 



variety onion couch or knot grass. It is therefore probable 

 that on most farms there must always be a large natural reser- 

 voir of flies. 



In the late summer or autumn the female Frit fly lays her 

 eggs on the leaves or stems of grass, and possibly, though there 

 is little evidence of this, on vtinter wheat and winter oats. The 

 eggs hatch quickly and the young larva make their way to the 

 centre of the shoot, which they destroy. As a rule, throughout 

 the winter, the minute white grub may be found, close down 

 to the base of the shoot; it is about Jth inch in length and 

 without legs. In the spring the grub changes to a pupa 

 inside a reddish brown pupa-case or puparium, either at the 

 point where it has been feeding or at various heights under 

 the outer leaf sheaths. The date of emergence of the frit fly 

 pupa is governed largely by weather conditions. Usually it 

 occurs in England from the middle of April to about the middle 

 of ]May. The date of the first appearance or at least the period 

 of maximum emergence of the spring brood, is of the utmost 

 importance to farmers, for if the young spring corn is 

 sufficiently advanced in growth at this date, proof exists that it 

 will be immune to attack, at least for all practical purposes. 

 The adult fly is of a brightly shining black, except for the 

 yellowish or brownish legs, and has a characteristic short 

 hopping flight. The female flies, appearing in April or May, 

 lay their eggs on the spring-sown oats and the resulting larvae 

 pass through similar transformations, doing the same injury to 

 the plant as the previous generation, but the time spent in 

 undergoing these transformations is shorter, lasting from six to 

 eight weeks. During July the flies of the second generation 

 appear, ready to lay their eggs in the ears of the young corn. 

 The third generation appears during August and September, the 

 females laying their eggs on grasses and occasionally perhaps 

 on autumn-sown corn. 



To control the pest on oats, the object is to get the young oat 

 plant forward as rapidly as possible. Growth may be accelerated 

 by the use of stimulating manures, which should be readily 

 available. Nitrogenous manures are of most importance. As 

 far as frit fly is concerned, the manure is needed chiefly during 

 the early stages of growth and may even be harmful if used too 

 freely, as it tends to cause lodging. For this reason, therefore, 

 moderate dressings, say J to 1 cwt. of sulphate of ammonia 

 nlong with 2 cwt. of superphosphate per acre, should be applied. 

 Once an attack is far advanced, little can be done in the way of 



