CATTLE-TSETSE CONTACT IN RELATION TO THE DAILY ACTIVITY PATTERNS OF GLOSSINA-MORSITANS SUBMORSITANS IN THE GAMBIA

The daily flight activity patterns of one of the main vectors of anima l trypanosomiasis in West Africa, Glossina morsitans submorsitans, wer e assessed using four different methods. Results from all the methods showed that there was some flight activity nearly every hour in all se asons but they differed in the level of contact between grazing cattle herds and G. m. submorsitans. In the late dry season, trap data indic ated that there was negligible activity from midday to late afternoon, whereas observations of tsetse contact with cattle herds or hand-net collections on herd followings showed no fall in attack rates on the c attle by G. m. submorsitans. Differences between trap and animal-baite d collection data may be attributable to the type of G. m. submorsitan s sampled by each method. Male G. m. submorsitans captured by traps we re more fat depleted than those caught on ox-baited flyrounds or by ha nd-net collections on herd followings. All methods showed that male G. m. submorsitans were most fat depleted in the late dry season and lea st in the early dry season. It was concluded that the traps were mainl y sampling the spontaneous flights of G. m. submorsitans. Hunger and e ndogenous rhythms increase the likelihood of spontaneous flights towar ds dusk, particularly in conditions such as those at midday in the ver y hot, late dry season. However, the presence of cattle herds in infes ted habitats probably activated nearby G. m. submorsitans and the cont inual movement through the grazing areas ensured contact with tsetse t hroughout grazing. The data indicated that strategic management of her d grazing times cannot eliminate the risk of trypanosomiasis transmiss ion occurring, irrespective of the harshness of the dry season climate . An assessment of the level of this risk could only be measured suita bly by collecting tsetse using animal-baited methods, not from trap da ta.