When are tsetse active?
Like us, tsetse have an innate pattern of activity. The savannah species, such as G.morsitans and G. pallidipes, are active mostly for the first two hours and the last two hours of the day (Hargrove & Brady, 1992). Many of the riverine species such as G. fuscipes are active in the middle of the day (Crump & Brady, 1979). There are exceptions to these generalities: the savannah species G. longipennis is most active just after sunset (Kyorku & Brady, 1994) and G. austeni, another savannah species, is active in the middle of the day.
These innate rhythms are influenced by temperature and thus the cool of a June morning in Botswana, when temperatures are less than 14°C can suppress the early morning peak of activity. Conversely, high (>32°C) afternoon temperatures, such as occur in the Zambezi Valley of Zimbabwe in October, can suppress the afternoon activity. But tsetse need to feed and so when one peak is suppressed then the other compensates. For example, on very hot days in Zimbabwe, tsetse are most active in the early morning.
Crump, A.J. & Brady, J. (1979). Circadian activity patterns in three species of tsetse fly: Glossina palpalis, austeni and morsitans. Physiological Entomology 4, 311-318.
Hargrove, J.W. & Brady, J. (1992) Activity rhythms of tsetse flies (Glossina spp.) (Diptera Glossinidae) at low and high temperatures in nature. Bulletin of Entomological Research, 82, 321-326.
Kappmeier, K. (2000). Diurnal activity patterns of Glossina brevipalpis and G. austeni (Diptera: Glossinidae) in South Africa, with reference to season and and meteorological factors. Onderstepoort Journal of Veterinary Research 67, 179-189.
Kyorku, C. & Brady, J. (1994). A free-running bimodal circadian rhythm in the tsetse fly Glossina longipennis. Journal of Insect Physiology 40, 63-67.