Distribution and population size of Glossina fuscipes fuscipes (tsetse flies) along the Lake Victoria, for trypanosomiasis management in Tanzania

O Manangwa, J O Ouma^1,2, I Malele, A Msangi³, F Mramba⁴ and G Nkwengulila⁵

Tsetse & Trypanosomiasis Research Institute, P. O. Box 1026, Tanga, Tanzania
okijanga@yahoo.com
¹ Africa Technical Research Centre, Vector Health International (VHI), P.O. Box 15500, Arusha,Tanzania
² Trypanosomiasis Research Centre, Kenya Agricultural Research Institute, P.O. Box 362, Kikuyu, Kenya
³ Directorate of Research & Training, Ministry of Livestock Development and Fisheries
⁴ Tanzania Veterinary Laboratory Agency (TVLA) P. O. Box 9154, Dar es Salaam, Tanzania
P. O. Box 9152, Dar es Salaam, Tanzania
⁵ Department of Zoology, University of Dar es Salaam, Tanzania, P. O. Box 35064, Dar es Salaam, Tanzania

Abstract

Glossina fuscipes fuscipes is among the important tsetse species of economic importance in Tanzania. The fly has a wide geographic distribution in sub-Saharan Africa. The information on distribution and population size of any fly specie is crucial when planning control strategies against tsetse as it helps to tell where to start traps deployment as well as estimate of the number of traps to be deployed on a particular area. Population size and distribution estimate studies were carried out along the shores of Lake Victoria in Tanzania. The study involved Kirongwe, Masonga, Rasi Nyabero and Tobwe River villages in Rorya district, Msozi village in Ukerewe district and Kemondo village in Bukoba district.

The results showed that the species is widely distributed along the shores of Lake Victoria. It extends from the north east of the Lake in Kirongwe village in Rorya district that borders Kenya to Kinase village that border Musoma district. It further extends to the north west of the Lake Victoria to Rubafu Ruina villages that border Uganda and also in Kemondo areas, just close to Bukoba town. Flies were also found in small visited Islands in Rorya district namely, Bugambwa and Ngonshe in Suba division. The biggest, Ukerewe Island was also infested with G. f. fuscipes in Msozi village and Namabugo village near Nansio town. Masonga had the highest fly abundance of 9.10 ± 0.501FTD (fly per trap per day) compared to other villages while Tobwe River had the least abundance of 0.94 ± 0.501 FTD during the dry season. A similar trend was also observed for the wet season, Masonga had the highest abundance of 6.40 ± 0.501FTD and Tobwe River had the least abundance of 1.63 ± 0.501. Based on the results of this study, if control activities are to be undertaken, more traps and targets are needed in Masonga and Rasi Nyabero vilages than in Kirongwe and Tobwe River. Age structure results elucidate that many flies caught were young flies aging 0 to 14 days and few flies were in wing category 4, 5 and 6. The control technology to be used will be dealing with young generation of flies which are mainly tenerals and looking for mating thus can easily succumb to baits (traps and targets) if effectively executed. There was significant variation of traps performance between different study sites. Further research is required to clarify the cause of this variation with locations.

Keywords: age structure, fly abundance, tsetse control

Introduction

Tsetse fly, Glossina species occur throughout the continent of Africa but previously distribution range included the southern tip of the Arabian Peninsula (Ouma et al 2006); wherever they occur they threaten human health and affect agriculture development by transmitting pathogenic trypanosomes, which cause sleeping sickness to humans and nagana to domestic animals (Jordan 1986). The southern limit of tsetse distribution in Africa lie north of the line drawn from Banguela, in Angola to Durban, in South Africa (Ford 1962). The northern limits are roughly a line from Dakar in Senegal across Ethiopia and Mogadishu in Somalia on the east coast (Leak 1999).

For better success, the selection of appropriate control strategies for improving human health and livestock production should take into account the dynamic nature of any tsetse species distribution and changes in their abundance (Rawling et al 1993). One of the most important outcomes from the results of species distribution surveys could be the estimation of the area that could be involved during control operations. The survey outcomes would clearly define priority areas for tsetse control and also areas where domestic animals and humans could be at risk of contracting the disease. Survey results could also help in the evaluation of the costs of the control method, which could be implemented in tsetse control in the study area (Rawling et al 1993).

G. f. fuscipes is among the important tsetse species of economic importance along the shores of Lake Victoria in Tanzania. The fly has a wide geographic distribution in sub-Saharan Africa. The present range includes the Democratic Republic of Congo (DRC), northern Angola, western Kenya, Uganda, western Rwanda, western Burundi, southern Sudan, and western and northeastern Tanzania (FAO 1982). Before this study, very little was known on population size and distribution of G. f. fuscipes along the shores of Lake Victoria on the Tanzanian side. Such knowledge is required to enhance efficacy of population suppression because it will inform distribution and density of traps and targets to be deployed. It will provide important guidelines when implementing any control program, for example if one will require the use of the Sterile Insect Technique (SIT) as a control method it will be possible to determine where to release sterile males and the number to be released in a particular area. Therefore, the present study was conducted to improve our understanding on the population size and the distribution of G. f. fuscipes along the Lake Victoria shores for the purpose of planning an effective control strategy against the species in the Lake Victoria basin to improve livestock production and human health in the region.

Materials and methods

Tsetse collection and study area

Tsetse sampling was conducted along the Lake Victoria in six sites namely Kirongwe, Masonga, Rasi Nyabero and Tobwe River in Rorya district, Msozi in Ukerewe district and Kemondo in Rural Bukoba district (Map 1). Tsetse collection was done between September and October, 2010 for the dry season and July and August 2011, toward the end of the wet season. Generally all these areas experience a bimodal rainfall pattern, short rains fall between October and December and long rains from March to May. The average annual rainfall in the basin is estimated to be 1015 mm (Makalle et al 2008). Tsetse collection was done using biconical (Challier & Laveissiere 1973) and pyramidal trap (Goutex & Lancien 1986). Each trap was geo-referenced using a Global Positioning System (GPS) to be incorporated in a Geographical Information System (GIS) for map development purposes. Traps were deployed after every 150 - 200 meters (Vale 1998). Collected flies were aged and counted for abundance estimation.

Apparent density and age estimation

The age of female flies was determined using ovarian configuration analysis whereas for male flies wing fray analysis was used (Pollock 1986). All tsetse captured per trap per day were counted and recorded. The apparent density, which is relative to the type of sampling tool (trap) used, is expressed as the average number of flies caught per trap per day (flies/trap/day or FTD).The apparent density was estimated as fly per trap per day (Saini & Simarro 2008).

Data analysis

Data were analyzed using SAS program (SAS 2000) where mean abundances of catches from different villages were compared and summarized by Analysis of Variance (ANOVA). Msozi (Ukerewe) and Kemondo (Bukoba) villages were excluded in the data analysis because there were no abundant data for the wet season.

Results

Results indicated that G. f. fuscipes is widely distributed along the shores of Lake Victoria. The specie is found on vegetation that is very close to water (in a strip of about less than 10 m away from the water level). When the traps were set 10 m away from water no flies were caught. The species extends from the north east of the Lake in Kirongwe village in Rorya district that borders Kenya to Kinase village that borders Musoma district. It further extends to the north west of the Lake Victoria to Rubafu Ruina villages that border Uganda and also in Kemondo areas close to Bukoba town. Flies are also found in small Islands in Rorya district namely, Bugambwa and Ngonshe in Suba division. The biggest Ukerewe Island is also infested with G. f. fuscipes in Msozi village and Namabugo near Nansio town.

Table1 above shows the mean abundances of G. f. fuscipes sampled in the four villages of Rorya district in Mara region for the wet and dry seasons. Masonga had the highest fly abundance (9.10 ± 0.501) compared to other villages while Tobwe River had the least abundance (0.94 ± 0.501) during the dry season. A similar trend was also observed for the wet season, Masonga had the highest abundance (6.40 ± 0.501) and Tobwe River had the least abundance (1.63 ± 0.501). The overall village mean abundance obtained in the four villages for both seasons varied significantly (P > 0.01). The mean variation of the fly abundances was further portioned by analysis of variance (ANOVA) to give the extent of variation; the results showed that season and number of sampling days had no significant difference (P < 0.005) in the mean abundance of G. f. fuscipes in different villages. However villages contributed significantly (P > 0.005) on the variation of mean abundances of all surveyed villages.

Age structure results of G. f. fuscipes for the wet and dry season

Age structure results indicated that more than 50% of the caught G. f. fuscipes were found in wing fray category one during the dry season (Table 3). These were flies with less than 12 days and few flies were in wing fray category 4, 5 and 6. Similarly, for the wet season the age of majority flies were falling in wing fray category one though the percentage were slightly lower compared to the dry season but the percentages were higher compared to wing fray category 2-6 in all villages. Estimated age varied from 11 days to19 days.

The performance of pyramidal and biconical traps varied with village. The variation of the trap performance was inconsistency. In Kirongwe village biconical trap had no significant difference (P > 0.6150) with pyramidal trap. However there was significant variation of trap performance in Rasi Nyabero, Masonga and Tobwe River (0.2356 ≤ P ≥ 0.0001).

Discussion

A proper understanding of the natural dynamics of the tsetse populations in the field is critical for determining which control strategy is appropriate for tsetse control (Echodu et al 2011; Rogers and Randolph 1986).Population dynamics is determined by both life history and ecological correlates such as mating system, dispersal ability and population size (Echodu et al 2011). This information is important as it identifies the priority areas for the control of the flies and places where people and livestock are at risk of contracting trypanosomiasis disease (Leak 1999; Rogers and Randolph 1986).

The population size of G. f. fuscipes estimated in the different villages under study varied significantly from one village to another. The abundance of flies was low along the Tobwe River and at Kirongwe village during both the wet and dry seasons. Kirongwe had poor stony soil accompanied by big stones. The soil couldn’t probably support good vegetation which would have favored tsetse multiplication and some areas were without enough vegetation and they were always dry. Tsetse distribution and abundance is a result of interaction between tsetse population with biotic factors which regulate their population size as well as their distribution limits Rogers & Randolph 1985). However other factor could be due to abiotic stresses such as drought, high salinity, and cold temperatures that are common adverse environmental conditions that significantly influence plant growth and productivity worldwide (Lata et al 2011). Other factors could be due to lack of suitable hosts where tsetse could feed. Since these areas have little vegetation few potential hosts could be found like wild animals specifically in Kirongwe village. In Rasi Nyabero vegetation clearance for vegetable growing was observed during the end of wet season though the mean abundance of G. f. fuscipes was greater; if there could be no vegetation clearance the mean abundance obtained in this study could be probably higher than the one obtained in the present study. The steady increase in the human population and the demand for land and firewood was reported to have an adverse effect on the continuity of tsetse habitat in Gambia (Rawling et al 1993; Hargrove et al 2000). From the results (see table 2), season had no significant (P < 0.005) effect on the tsetse population size; this is contrary to what is reported in the literature. The possible reason for this discrepancy could be flies are confined to a narrow strip of vegetation which is less than 10 meters away from the water level; hence the vegetation does not depend on rainfall as there is water throughout the year. Similar observation was reported in Angola that G. f. fuscipes was confined to hydrophytic habitats, such as forested patches along rivers and lacustrine environments (Machado 1954).

Based on the results of this study, if control activities are to be undertaken more traps and targets are needed in Masonga and Rasi Nyabero vilages than in Kirongwe and Tobwe River. One trypanosomiasis case in G. f. fuscipes was detected in Rasi Nyabero; this shows that there was a direct correlation between fly abundance and trypanosomiasis though we had no trypanosomiasis case in Masonga. Usually the fly abundance, and the risk of disease transmission, is greatest at the optimum bioclimatic for each tsetse species (Rogers and Randolph 1986).

Distribution results showed that flies were caught at the border of Uganda and Kenya; therefore if control activities are to be implemented it will be important to collaborate with the neighboring countries to avoid a problem of reinvasion. The result of this study is important in the tsetse control activities in Tanzania but also to other affected African countries as advocated by Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). PATTEC advocates a progressive elimination of discrete areas of tsetse populations using a combination of methods depending on fly species, terrain and habitat, and local and national experience in affected African continent in the shortest time as possible (Kuzoe & Schofield 2004). G. f. fuscipes could be one of the species that could be tackled collectively among East African countries in order to halt transmission of trypanosomiasis and thus expand livestock sector and human health in the region (Kabayo 2002).

Age structure results elucidated that many flies caught were young flies aging from 0 to 14 days and few flies were in wing fray category 4, 5 and 6. The control technology to be used will be dealing with young generation of flies which are mainly teneral and looking for mating thus can easily succumb to baits (traps and targets) if effectively executed.

The trap performance study indicated significant variation between pyramidal and biconical traps between surveyed villages. Similar results were obtained by (Kaba et al 2014) who found inconsistency variation of the trap performance of Glossina palpalis palpalis catches in central and West Africa when monoconical and pyramidal traps was used. The source variation of trap performance in the present study could be a result of intrinsic and extrinsic factors experienced during trapping period (Ziba et al 1994). Further research is required in establishing the source of variation of trap performance in the field at different locations to improve our understanding on trap efficacy. 

Conclusion

• G. f. fuscipes is widely distributed along the shore of Lake Victoria from north eastern Tanzania (Kenya border) as far as northwestern Tanzania (Uganda border); it is also found in all visited small Islands namely Bugambwa and Ngonshe in Suba division in Rorya district in Musoma and the big Ukerewe Island in Mwanza region. The population size of the species was significantly lower in Tobwe River and Kirongwe village and highest in Masonga and Rasi Nyabero villages; season had no significant (P > 0.05) effect on the fly abundance. Intensive application of integrated tsetse control methods such as traps and insecticide treated targets could easily get rid of the species population in area especially due to its restriction to the areas near the lake. If need be, Sterile Insect Technique (SIT) could be used to completely eradicate the species in the area. SIT works well in the areas which are dominated by single species like G. f. fuscipes in this area. However for the use of traps and targets against the species for suppression and control, a high density of traps and targets will be required in Masonga and Rasi Nyabero villages than in Kirongwe village and Tobwe River. The performance of pyramidal and biconical traps in catching G. f. fuscipes was inconsistency in different villages hence one cannot rely on this results. More research is required to find the sources of these reported variations from different study sites in the study area.

Acknowledgements

We are particularly grateful to the technical staffs of TTRI for technical assistance and TTRI management for logistics. Many thanks are due to World Health Organization (WHO) for funding this work through TTRI project.

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Received 13 August 2014; Accepted 27 December 2014; Published 4 February 2015

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