BackgroundTsetse flies are the cyclical vectors of African trypanosomosis that constitute a major constraint to development in Africa. Their control is an important component of the integrated management of these diseases, and among the techniques available, the sterile insect technique (SIT) is the sole that is efficient at low densities.The government of Burkina Faso has embarked on a tsetse eradication programme in the framework of the PATTEC, where SIT is an important component. The project plans to use flies from a Glossina palpalis gambiensis colony that has been maintained for about 40 years at the Centre International de Recherche-Développement sur l'Elevage en zone Subhumide (CIRDES). It was thus necessary to test the competitiveness of the sterile males originating from this colony.Methodology/Principal FindingsDuring the period January–February 2010, 16,000 sterile male G. p. gambiensis were released along a tributary of the Mouhoun river. The study revealed that with a mean sterile to wild male ratio of 1.16 (s.d. 0.38), the abortion rate of the wild female flies was significantly higher than before (p = 0.026) and after (p = 0.019) the release period. The estimated competitiveness of the sterile males (Fried index) was 0.07 (s.d. 0.02), indicating that a sterile to wild male ratio of 14.4 would be necessary to obtain nearly complete induced sterility in the female population. The aggregation patterns of sterile and wild male flies were similar. The survival rate of the released sterile male flies was similar to that observed in 1983–1985 for the same colony.Conclusions/SignificanceWe conclude that gamma sterilised male G. p. gambiensis derived from the CIRDES colony have a competitiveness that is comparable to their competitiveness obtained 35 years ago and can still be used for an area-wide integrated pest management campaign with a sterile insect component in Burkina Faso.

Spatio-temporally heterogeneous environments may lead to unexpected population dynamics. Knowledge is needed on local properties favouring population resilience at large scale. For pathogen vectors, such as tsetse flies transmitting human and animal African trypanosomosis, this is crucial to target management strategies. We developed a mechanistic spatio-temporal model of the age-structured population dynamics of tsetse flies, parametrized with field and laboratory data. It accounts for density- and temperature-dependence. The studied environment is heterogeneous, fragmented and dispersal is suitability-driven. We confirmed that temperature and adult mortality have a strong impact on tsetse populations. When homogeneously increasing adult mortality, control was less effective and induced faster population recovery in the coldest and temperature-stable locations, creating refuges. To optimally select locations to control, we assessed the potential impact of treating them and their contribution to the whole population. This heterogeneous control induced a similar population decrease, with more dispersed individuals. Control efficacy was no longer related to temperature. Dispersal was responsible for refuges at the interface between controlled and uncontrolled zones, where resurgence after control was very high. The early identification of refuges, which could jeopardize control efforts, is crucial. We recommend baseline data collection to characterize the ecosystem before implementing any measures.

A spatially and temporally heterogeneous environment may lead to unexpected population dynamics. Knowledge still is needed on which of the local environment properties favour population maintenance at larger scale. For pathogen vectors, such as tsetse flies transmitting human and animal African trypanosomosis, such a knowledge is crucial to design relevant management strategies. We developed an original mechanistic spatio-temporal model of tsetse fly population dynamics, accounting for combined effects of spatial complexity, density-dependence, and temperature on the age-structured population, and parametrized with field and laboratory data. We confirmed the strong impact of temperature and adult mortality on tsetse populations. We showed that the coldest cells with the smallest variations in temperature acted as refuges when adult mortality was homogeneously increased, control being less effective in such refuges. In contrast, targeting the cells contributed the most to population management, i.e. those of highest carrying capacity and the most impacted by increased mortality, resulted in a decline in population size with a similar efficacy, but resulted in more dispersed individuals, control efficacy being no longer related to temperature. Population resurgence after control was slow, but could be very high locally in refuges, with highly contrasted situations after a heterogeneous control, refuges being located at the interface between controlled and uncontrolled zones. Our results highlighted the importance of baseline data collection to characterize the targeted ecosystem before any control measure is implemented. palpalis gambiensis population of the Niayes (Senegal), a region with an ongoing eradication project 69 (Dicko et al. 2014; Vreyssen et al. in press). In this area, less than 4% of the habitat was considered 70 favourable for G. p. gambiensis (Bouyer et al. 2010), and the tsetse populations were highly structured 71 across the metapopulation (Solano et al. 2010b). This knowledge was incorporated in the model, 72accounting for combined effects of spatial complexity, density-dependence, and temperature on the 73 age-structured population. 74 Material and methods 75

L’objectif de cette étude a été de comparer l’efficacité de deux méthodes d’application du triflumuron sur des glossines mâles pour le transfert du produit aux femelles pendant l’accouplement. La méthode topique, avec dépôt de la solution sur la partie supérieure du thorax, a été utilisée pour quatre groupes de 150 glossines mâles âgées de six jours ayant reçu 1 μg, 2 μg et 5 μg de triflumuron contenu dans 1 μl d’eau, et le témoin ayant reçu de l’eau. Chaque groupe de mâles a été ensuite successivement accouplé avec trois groupes de 150 femelles âgées de trois jours pendant 48 h. Les effets mesurés ont été les taux d’avortement et d’éclosions des pupes, la forme et le poids des pupes. L’analyse des résultats sur les quatre premiers cycles de reproduction des femelles a montré des différences significatives entre les taux d’éclosions chez les femelles accouplées avec les mâles traités aux doses de 2 μg et 5 μg et les taux d’éclosions chez les femelles du lot témoin, uniquement au premier cycle du premier accouplement (p < 0,05). La deuxième méthode a consisté à asperger un jet de 0,8 ml de solution à 3 p. 100 de triflumuron sur un groupe de 200 mâles, soit en moyenne moins de 1 μg/mouche. Le groupe de mâles ainsi traités et le groupe témoin traité à l’eau ont été accouplés successivement à trois groupes de femelles comme précédemment. Les résultats ont montré non seulement des différences très significatives lors des quatre cycles de reproduction du premier accouplement, mais également au deuxième accouplement entre les moyennes des taux d’éclosions (p < 0,001). Au premier accouplement, la moyenne des taux d’éclosion lors des quatre premiers cycles chez le lot traité a été de 43,7 ± 22 p. 100 contre 89,0 ± 0,5 p. 100 chez le témoin. Le transfert du triflumuron des mâles traités (5 μg/mouche) par application topique aux femelles pendant l’accouplement a été peu efficace par rapport à la méthode d’aspersion.

No abstract