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A method of assessing the population of wheat‐blossom midges by the recovery of the cocoons from soil is described. In the dry summer of 1947, considerable numbers of larvae of Sitodiplosis mosellana Géhin were still in the ears at the time of harvesting. Burning the straw immediately after combining may considerably reduce the numbers of midges. The majority of the larvae are found in the top 3 in. of the soil although a considerable number may be found from 3 to 6 in. Headland infestations may be lighter than the rest of the field. Cocoons of S. mosellana remain viable in the soil for several years, and 150,000 per acre were recovered in February 1951 from a field which had not had a wheat crop since 1944. At the same time 50,000 Contarinia tritici Kirby cocoons per acre were found in a field which was last under wheat in 1947. Viable pupae were successfully obtained by soil sampling, and the pupation in the soil and subsequent emergence of the midges can be followed. Thus it is possible also to estimate the numbers of midges that will emerge. Progress has been made towards predicting outbreaks of these two midges.

THIS work extends studies on the fauna of bacteria beds of sewage works in which it was shown that interspecific competition for a limited food supply leads to a reduction in the numbers of the various flies breeding in the beds (Lloyd, 1937; Lloyd et d. 1940). Routine observations at one station with a moderately varied fauna have been paralleled with exactly similar records at another where the fauna is so restricted that the competition may be considered to be practically intraspecific. The observations have been continuous from October 1937 to April 1939 and have included the study and assessment of the fly ouput together with observations on the physical environment such as temperature, acidity and the nature of the medium. Further, the distribution of the larvae and pupae has been studied. As a result it has been possible to throw light upon certain aspects of competition between these flies, including the relation of size to temperature and crowding, and the significance of inter-and intraspecific competition. MATERIAL AND ~O D SThe statiom where these observations were carried out were Huddersfield (Cooper Bridge) and Knostrop (Leeds). Bad& be& The beds at Huddersfield are circular, 200 ft. in diameter and raised 7 ft. above the ground level. They are open-sided and the medium is of clinker. The sewage is distributed in jets by means of four arms which revolve quickly taking only 2-3 min. to complete a revolution. The cavities in the medium afford protection for all stages of the flies. T w o beds were used for study, one (no. I) with surface clinker consisting of pieces 1-2 in. in diameter and the other (no. 2) of 4 in. pieces.At Knostrop the beds are rectanguh and sunk to the ground level. The medium is of water-worn gravel, covered during most of the year with a growth of the blue-green alga, PhoTmidium (Reynoldson, 1939). The sewage is delivered in sheets, the distributing arms travelling slowly, taking f hr. to traverse the length of the bed. D e h i t e resting &ods are not the rule at either place. At Huddersfield each machine is stopped daily at any time for periods totalling 12-16 hr. (not continuously). The length of the rest depends chiefly on the m o u n t of sewage to be treated, the rests being shorter or even absent during periods of heavy rainfall and longer during drought. Hence, although the surface of the bed may dry during these stoppages, there is no serious effect upon the fauna as the rest is never prolonged and only the top layer of 2-3 in. is affected. Bed temperatures were recorded at both places, and the Knostrop beds were found to be slightly cooler on the monthly mean ( Table 9). Character of sezuage and treatmentThe character of the sewage at Huddersfield is dominated by the waste products of the dye works in the district and consequently is acid in reaction. The crude sewage at times has a pH 3-4. It is neutralized by means of lime SO that the water reaching the beds averages pH 6-7. Lime is not added on Sundays, and hence very acid sewage is delivered on to the beds for se...

35All treatments, with the possible exception of trichlorphon, gave some measure of control, but fenitrothion and the higher rate of chlorfenvinphos gave the most complete kill.

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