Factors Influencing the Abundance and Size of Psychoda Species in Sewage Bacteria Beds

Abstract

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...

Some causes of size variation in the pea aphid, Acyrthosiphon pisum Harris

“…However, in general, published evidence shows that individual size of many species does not decrease until a critical high density is reached: for example, in Psychoda spp. (Golightly & Lloyd, 1939;Golightly, 1940).…”

“…(Howe & Currie, 1964); Psychoda spp. (Golightly & Lloyd, 1939;Golightly, 1940). There is much less evidence to suggest that low temperatures also cause size decrease in insects (Uvarov, 1931 ;Burges & Cammell, 1964).…”

The biological consequences of decreased size caused by crowding or rearing temperatures in apterae of the pea aphid, Acyrthosiphon pisum Harris

“…A direct relationship between size, usually weight, and fecundity has been demonstrated for a range of insect species, for example Psychoda species (Golightly, 1940); Hofmannophila pseudospretalla (Stainton) (Woodroffe, 1951~) ; Endrosis sarcitrella (L.) (Woodroffe, 1951 b); Plutella maculipennis (Curtis) (Atwal, 1955); Cadra cautella (Walker) (Takahashi, 1956). Direct counts of the progeny produced are often tedious, and assessments of potential fecundity are often made by relating ovariole numbers to size (Webber, 1955;van den Newel, 1963); ovarioles, however, vary in their productivity (Webber, 1955).…”