Long-term fluctuations in numbers of the tsetse fly Glossina swynnertoni Austen

E-ISSN： 1475-2670|53|1|129-137

ISSN： 0007-4853

Source： Bulletin of Entomological Research, Vol.53, Iss.1, 1962-05, pp. : 129-137

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Abstract

The tsetse fly population of Block 9 at Shinyanga, Tanganyika, consisting of 40–50 square miles of thorn bush, was studied from 1935 to 1957 by means of fly-rounds with a total length of 30 miles. The mean annual apparent density (A.D.) of Glossina swynnertoni Aust., taken as the geometric mean of the 12 monthly figures, is plotted on a graph covering 23 years, together with data for 1930–36 from another block which, however, is only doubtfully comparable. Four peaks and five troughs occur on the graph of Block 9, the highest value being 18 times the lowest. The history of the natural and artificial events which have occurred in the block are detailed as far as they are known. The minimum A.D. was that of 1938, after a number of wild animals had died of rinderpest; thereafter, the A.D. rose for several years, in spite of certain anti-tsetse measures, and none of the fluctuations subsequent to 1938 can be associated with any natural or artificial event. The amplitude of the fluctuations is small compared with records in the literature for other animal populations, and their occurrence is irregular; the last peak observed was in 1954, but limited observations in 1959 gave catches little, if at all, below those of 1954.