Number of tabanids caught with trap type.
To embark on an anti-vectorial fight against mechanical vectors of animal trypanosomosis, investigations were undertaken in order to determine the abundance, species diversity and daily activity of tabanids in a cattle ranch in Gabon. The nzi and vavoua traps were used to catch tabanids in three divisions of this ranch. In this study, 616 tabanids were captured: 349 (56.66%) in Division 1, 226 (36.69%) in Division 2 and 41 (6.66%) in Division 3. In the first Division, T. taeniola was the most abundant species with an Apparent Density (ADT) of 2.2, followed by H. pluvialis (ADT = 1.05). In the second Division, H. pluvialis was most abundant with ADT of 1.6, followed by T. taeniola (ADT = 0.38). In the last Division, the most abundant species was H. pluvialis (ADT = 0.15). Comparing the relative abundance of catches with sites (Divisions), we realized that there was no statistically significant difference in catches with trapping sites. It was noticed that Division 3 recorded the highest diversity index values. We realized that the nzi trap recorded higher tabanid catches than the vavoua trap. The diurnal activity rhythm of the most frequent species encountered slightly differed with prospection sites.
Insects are necessary creatures to the living world [1, 2]. Indeed, they are involved in many processes and mechanisms essential for the functioning of ecosystems  for example, honey bees, domestic flies and butterflies pollinate our crops [4, 5, 6]. Other groups of insects play the role of predators of certain species such as wasps and ladybugs that attack caterpillars and aphids that destroy plants . Similarly, beetles and flies guarantee the decomposition of organic matter, playing a major role in the recycling of essential nutrients to primary producers . However, there are also insect species, including hematophagous dipterans such as tabanids that play a role in the transmission of several pathogens responsible for many diseases . In fact, tabanids are known to be mechanical vectors of trypanosomes including
Presently, there are approximately 4400 known species of tabanids [17, 18]. In Gabon, knowledge on tabanids in livestock farms is lacking. However, previous studies conducted by Mavoungou et al.  and Zinga et al. [19, 20] at the Ivindo National Park showed that several tabanid species co-existed in sympatry in the different biotopes prospected. In addition, the report of Obame et al.  in traditional livestock farms in north Gabon highlighted the presence of blood-feeding flies in this region. Regarding the weakly documented information on tabanids in livestock farms in Gabon, an entomological prospection to determine the abundance and species diversity is indispensible if control operations are to be conducted in this part of the country .
In the Nyanga ranch (located in southern Gabon), trypanosomosis is the most common disease of livestock. This disease causes fever, anemia and death in infected animals . In order to establish effective control strategies against tabanids, mechanical vectors of animal trypanosomosis, an entomological study was undertaken to determine their abundance, species diversity and daily activity in the Nyanga cattle ranch.
2. Materials and methods
2.1 Study zone
This study was conducted in the Nyanga Ranch. It is a cattle farm located in the Nyanga province in the south-west of Gabon (Figure 1).
The ranch covers an area of 100,000 ha and was created for the breeding of more than 6000 cattle heads . It is made up of three divisions, each of which has its own individual characteristics.
Division 1 has an area of 30,000 ha. It consists of six (6) sections: Bibonga, Galla, Mibamba, Upper Douki, Nyanga and Lower Douki. About 851 animals are reared in this division. In addition, the vegetation of this site is savanna-like.
Division 2 covers nearly 30,000 ha. It is dedicated for breeding, selection and fattening of males. It receives all males (bulls and oxen) after the weaning stage. This division is subdivided into three sections: Kouri, Moukenlengui and Povo. A total of 1754 animals are present in this division. The vegetation of this division consists of savannas and forest galleries.
Division 3 covers an area of 40,000 ha and includes four (4) sections: Yaba, Douli, Voungou and Douxila. This division is used for cattle breeding. Here, there are cows, heifers and calves that are kept until weaning. More than 2500 animals are reared in this division and the vegetation of this division is savanna and forest.
In general, the vegetation of the Nyanga Ranch area is made up of savannas and forest galleries colonized by many plant families including members of the subfamily Gramineae. The area has a rich and diverse fauna including elephants (
The Nyanga Ranch region has an equatorial climate marked by alternating rainy and dry seasons. The rainy season spans from October to April, while the dry season occurs from May to September . The average annual rainfall is 2000 mm in the North and 1600 mm in the South.
2.2 Capture and identification of tabanids
Tabanids were captured using the vavoua (constructed by Laveissière & Grébau  and nzi (constructed by Mihok  (Figure 2a and b) traps. A total of 10 traps were set in each division of the Nyanga Ranch, including 5 traps of each type, spaced approximately 30 m apart. Each of the two traps constituted a capture point in the trapping sites. Flies were collected daily. Trapping was conducted from 9th October to 14th December 2016 with total trapping duration of 60 days.
In each division, three nzi traps separated by at least 500 m distance were set to evaluate the daily activity of tabanids. The flies were collected systematically every two hours from 8 h to 18 h. The captured flies were put in well labeled vials.
2.3 Fly identification
2.4 Data analysis
The apparent density (ADT) of each species of tabanids was defined as the number of flies caught per trap per days and calculated using the following formula (1):
The biodiversity index of Shannon, which quantifies the heterogeneity of individuals in an environment, was calculated using the following formula (2):
Ni is the number of individuals of a given species.
N, the total number of individuals.
The Simpson index, which is used to determine the probability that two randomly selected individuals in a given milieu are of the same species was calculated using the following formula (3):
The Piélou Equitability Index, also known as the Equity Distribution Index, was calculated according to the formula (4):
Where S, is the number of species.
The non-parametric Kruskal-Wallis test was used to compare catches with trapping sites. The statistical test was performed using the XLSTA software version 3.01.19349. The statistical significance level was kept at p < 0.05.
3.1 Genera composition of tabannids
A total of 616 tabanids divided into 5 genera and 18 species were recorded in this study. The following genera were identified:
3.2 Species composition with trap type
Regarding fly catches with trap types, we noticed that the nzi trap captured more tabanids than the vavoua trap (Table 1).
3.3 Proportion of tabanid species
In total, 17 species of tabanids were recorded throughout the survey. The genus
3.4 The abundance of tabanids with trapping site
Of the 616 tabanids caught in the Nyanga Ranch, 349 (56.66%) came from Division 1, 226 (36.69%) from Division 2 and 41 (6.66%) from Division 3. Of the 8 species of tabanids caught in Division 1,
In Division 2, 13 species were captured and
In Division 3, 10 species were captured and
3.5 Diversity of tabanids
The results of the ecological indices are presented in Table 2. Division 3 showed the highest values in terms of biodiversity index.
|Ecological indices||Division 1||Division 2||Division 3|
|Equitability index of Pielou||0.68||0.58||0.78|
The non-parametric Kruskal-Wallis test showed that the species of tabanids caught did not differ statistically with division (Table 3).
|K (observed value)||1.848|
|K (critical value)||5.991|
3.6 Daily activity of the most frequent species of tabanids with respect to prospection divisions
3.6.1 Diurnal activity pattern of
H. pluvialisand T. taeniolain division 1
In division 1,
3.6.2 Diurnal activity pattern of
H. pluvialisand T. parin division 2
The diurnal activity pattern of
3.6.3 Diurnal activity pattern of
H. pluvialisand T. taeniolain division 3
In Division 3,
This study is a preliminary inventory of tabanids, mechanical vectors of AAT in the Nyanga ranch. The results obtained in this study indicates the presence of several tabanid species that live in sympatry in the Nyanga Ranch. Five genera and 18 species of tabanids were identified in this study. We noticed that divisions 1 and 2 were strongly infested by tabanids while division 3 was weakly infested. This distribution could be explained by the differences in the environmental and microclimatic factors of the divisions which might have created conditions more or less favorable for the development and survival of tabanids. This observation is similar to that made by Mavoungou et al. , Zinga et al. [19, 20] and Doumba et al. . These authors observed a heterogeneous distribution of tabanids following the structuring of the prospected milieu. The infestation of an ecosystem by haematophagous flies such as tabanids is defined by the simultaneous presence of many suitable environmental factors, such as temperatures between 15° C and 25° C, good luminosity, high relative humidity and the availability of vertebrate hosts [32, 33, 34]. These conditions occurred in Division 1 where maximum catches were made. However, ecological diversity indices especially the Piélou equitability index revealed that Division 3 represented high species diversity.
In addition, some tabanid species including
The dominant species observed in this study were
We found that the nzi trap caught more tabanids than the vavoua trap. This observation has been made by several authors who reported that tabanids are mostly attracted to the blue black color of the nzi trap and possibly their size and shape [14, 27, 39, 40].
The results on the daily activity of the various species of tabanids captured portrayed a variation in the number of catches with time of the day. These insects have an activity marked by peaks of abundance observed in the early morning between 8 h and 10 h and at dusk between 16 h and 18 h. In divisions 1 and 3, the activity peak reached between 12 h and 14 h whereas in division 2, the abundance occurred between 8 h and 10 h. These results are similar to those obtained by Mavoungou et al.  who showed the importance of hot hours of the day on the abundance of biting flies. Generally speaking, three main species,
This study identified 17 species of tabanids with
We thank all the workers of the Nyanga Ranch for assisting during field surveys.
Conflict of interest
The authors declare that they have no competing interests.