A quantitative survey of Wheat Bulb Fly (Leptohylemyia coarctata) was made in Yorkshire in 1945, and the distribution of the fly is discussed in relation to general observations and records in the years 1935–1946. The distribution is shown in themap (fig. 2).

One hundred and thirty-six fields on 86 farms were examined and Wheat Bulb Fly was present in over half of the farms and fields; in 8 fields (6 per cent.) it was present in moderately high numbers, and in 2 fields (1·5 per cent.) it was present in numbers sufficiently high to be likely to cause a failure in a bad wheat year. It was estimated that two or three thousand acres of wheat and rye in Yorkshire are likely to have a reduced crop as a result of Wheat Bulb Fly attack in an unfavourable season. Over half the dangerous area is near Selby. The only large area where Wheat Bulb Fly was virtually absent was the Yorkshire wolds.