Spontaneous, Circadian Components of Tsetse Fly Activity

Abstract

The spontaneous flight activity of Glossina morsitans was monitored in rocking-box actographs in constant conditions under different light régimes. The mean daily time spent in activity in the actographs (12·5 min) accords well with what is estimated for behaviour in the field. In all types of fly tested, a clear ‘V’-shaped diurnal pattern of activity occurred in LD 12 : 12. The morning peak comprised more activity than the evening peak, but for hungry flies roughly the same proportion of the population was involved at each time. The similarity between this spontaneous activity pattern in the laboratory and the diurnal pattern typically observed in the field suggests that it is unnecessary to invoke environmental control to explain the gross form of the latter. In DD a clear circadian rhythm emerged in the activity of teneral flies, though in LL this rhythm damped out after 2 to 3 cycles. These findings are discussed in relation to current theories of circadian rhythms. A linear daily increase in activity occurred during 5 days of starvation in all flies, except pregnant females, whose daily increase followed an exponential pattern, implying that a complex behavioural change results from the act of fertilization.