TSETSE-FLIES, BIODIVERSITY AND THE CONTROL OF SLEEPING SICKNESS - STRUCTURE OF A GLOSSINA GUILD IN SOUTHWEST COTE-DIVOIRE

Tsetse fly guilds usually comprise two or three species. However, the presence of only one species often indicates that anthropic modificati ons have occurred in the habitat. On the other hand, more than three s pecies are seldom observed in the same zone and the presence of five i s extremely rare. Previous detailed studies have always focused on a s ingle species, without taking into account interactions between specie s. The authors present the results of observations carried out in Cote d'Ivoire on a guild consisting of Glossina palpalis, G. pallicera, G. nigrofusca, G. longipalpis and G. Susca. Glossina have unusual physio logical characteristics: both sexes feed exclusively on blood, they ha ve a highly developed larviparity associated with a slow rhythm of rep roduction (one larva about every ten days) and a long life expectancy (up to nine months). The authors report on the size of the flies, the hosts, feeding habits, ecodistribution, resting-places, flying heights , circadian activity and seasonal dynamics of tsetse fly populations i n order to understand the organization of this guild. Each species fee ds indiscriminately on a wide spectrum of hosts without a particular p reference. Different species shared habitat (ecodistribution) and time (circadian and annual cycles). Thus, during an annual cycle, there is always a slight time-lag between the density peaks of G. palpalis and G. pallicera, the peak of the dominant species immediately preceding that of the dominated species. In a village area, 77 % of the variatio ns in density of G. pallicera were accounted for by the previous varia tions in density of the dominant species (G, palpalis). Experiments sh ow that G. pallicera and G. nigrofusca immediately invade anthropic ar eas from which G. palpalis has been partially removed by trapping. The se species thus appear to confront each other in a global dynamic equi librium. This suggests that there is a 'conflicting coexistence' betwe en the cohabiting species. Whereas the reason for such a process is qu ite obvious, how it occurs still remains to be explained. Other observ ations may provide a clue. For example, the sex ratios of both the mai n species fluctuate in opposite phases during the annual cycle, This s trongly suggests that interspecific interactions occur through sexual mediation. Finally, the authors discuss the consequences of dynamic co habitation on disease systems (trypanosomes, tsetse flies, hosts) and on control possibilities. (C) Elsevier, Paris.