106 Observations on the Habits o/Oscinella frit 



The breeding cages used were all normal with such slight modifica- 

 tions as were required. 



I am indebted to the Professor of Forestry for the provision of a 

 laboratory, to Professor Somerville for permission to use apparatus and 

 the part provision of an insectary, and to Mr J. E. Collin for freely placing 

 his knowledge of the frit-fly problem at my disposal. 



A. THE PREVALENCE OF THE ADULT FLY IN THE FIELD 

 DURING THE YEAR. 



Various authors in England have noted that the flies swarmed in 

 certain months or on certain days — Westwood(28) in July, Ormerod(2i) 

 on July 9th, 1888, Theobald (25) in August — while Conin(8) records 

 that "all stages are easily obtained between May and September." 

 Again, MacDougall (18) states that between June 21st and Sept. 29th he 

 collected the fly on many occasions. 



A general deduction from the meagre evidence available would be 

 that the fly is nearly always present in the field in the warm season, but 

 that it becomes very much more abundant both when the oat is in ear 

 and when the grain is ripe. 



To test the accuracy of this view, a regular series of field observations, 

 to determine the number of flies present on the crop throughout the 

 growing season, was made in 1919 and 1920. In conjunction with these 

 observations, controlled breeding experiments were conducted, to check 

 the field data. 



Method of Procedure. 



By the courtesy of the Professor of Rural Economy, the observations 

 were made on the University Farm, Sandford-on-Thames. To eliminate, 

 as far as possible, any large influx of flies released by disturbance of 

 other cereal crops, the field selected was one surrounded by meadowland, 

 the nearest cereal crop being a quarter of a mile distant. No information 

 is available as to the normal extent of grass infestation nor as to the 

 migratory powers of the adult fly. 



The plan (Fig. 1) indicates the relative areas and positions of the 

 crops grown in this field in 1919-20 and also the position (A) where 

 sweeping operations were conducted^. 



^ Observations of the Food Production Department in June, 1919, showed that, in 

 this jilot, 37-4 per cent, of the plants were badly attacked, 45-6 per cent, were attacked 

 but sending up ears, while only 17 per cent, were not attacked (in litt.). 



