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The sunset activity of tsetse flies: a light threshold study on Glossina morsitans
Author(s) -
BRADY JOHN
Publication year - 1987
Publication title -
physiological entomology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.693
H-Index - 57
eISSN - 1365-3032
pISSN - 0307-6962
DOI - 10.1111/j.1365-3032.1987.tb00762.x
Subject(s) - dusk , sunset , glossina morsitans , biology , light intensity , tsetse fly , photoperiodism , zoology , intensity (physics) , luminous intensity , botany , atmospheric sciences , ecology , physics , optics
. At dusk, tsetses fly from their day‐time resting sites on tree trunks to spend the night on leaves and twigs. At the end of the day in the laboratory, they show a few minutes of heightened activity which apparently represents this behaviour. This occurs immediately after lights‐out in a square‐wave LD cycle, but just before the end of a 30‐min artificial ‘dusk’ which mimics the natural change in light intensity at sunset. The activity is triggered when the declining light falls to a mean value of c. 350 mW m ‐2 . Accurate, 24‐h light measurements made in Zimbabwe show that in tsetse ‘bush’ this intensity occurs close to sunset. Neither the initial photophase light intensity (900 and 2500 mW m ‐2 were tested) nor the rate of dimming affect the critical value, which is also the same whether arrived at within c. 10 min in a ‘logarithmic dusk’ or within c. 20 min in a ‘linear dusk’. In newly‐emerged or recently fed flies, however, it is lower ( c. 50–100 mW m ‐2 ); and when a similar activity burst is induced by a ‘dusk’ at midday (i.e. at the flies' phase of minimum activity), the threshold is c. 200 m W m ‐2 . It is concluded that this short behavioural programme is primarily a direct response to a specific, low light intensity, but that the threshold is modified by circadian and other physiological inputs.