The region of Guéra (LN 09˚32'-13˚00' and LE 17˚00'-20˚00'), is a geographic transition zone between pastoral Sahelian and the agricultural Sudanian zones (Figure 1). It has a surface area of 61,280 km² with nearly 10 habitants per km scare [24] . The climate is of the Sudano-Sahelian type with the annual rainfall between 300 to 900 mm/year. The vegetation subjected to rainfall gradient and is woody or clear savanna according to latitude and relief. The hydrography is made up of some few streams which favor the circulation of underground water. The average annual temperature is 29.5˚C (minimum in December-January 18˚C and maximum in March 40˚C). The natural vegetation is Acacia woody Savannah. The major ethnic group in this region is Hadjaraï. The economy of this region is based on cereals (sorghum and maize), groundnuts and sesames production by women [24] . Traditional extensive apiculture is practiced.

Direct observations during Periodical field trips in rainy and dry seasons in 2014, between 6 a.m. and 6 p.m. were carried out. Plants whose flowers were foraged by workers bee for at least two minutes were considered as honeybee plants. Already known as melliferous plants in the literature were recorded, unknown and unfamiliar plants were identified using botanical field guides [25] - [27] . All the identified plants were classified according to botanic characteristics (biological type, flower color, degree of domestication). Some of the plants were photographed with a digital camera.

The quantitative data collected were treated using variance analysis with the aid of Statgraphic plus version 5.0.

A total of 52 melliferous plants divided into 16 botanic families were identified in the Guera region (Table 1; Figures 2-7). Mimosaceae with 37.25% of the bee plants indentified, was the most represented family followed

by Combretaceae and Poaceae (families repectively 07.84% and 05.88% of the beeplant species (Figure 8), while Balanitaceae, Cucurbitaceae, Malvaceae, Oleacea, Punicaceae and Tiliaceae where the least represented families with only one species. Acacia is the most frequent genera followed by Ziziphus.

In the savannah of north East Nigeria, Fabaceae and Combretaceae are families with highest number of melliferous species [5] . The number of melliferous plants identified is less than those collected in the other ecosystems, especially by Dukku [5] in the savanna zone of north East Nigeria that identified 61 species regrouped into 49 genus and 25 families. Among the fourth genera predominant (Acacia, Combretum, Ziziphus and Eucalyptus) in the north East of Nigeria, two were also frequently foraged by bees in our zone. In that same zone, Fabaceae and Combretaceae are the families with the highest number of plant species. In Burkina Faso, Sawadogo and Guinko [28] and in Côte d’Ivoire, Coulibaly et al. [29] identified respectively 118 (19 families) and 121 (45 families) bee plants. The genera with the highest number of species were Albizia and Ficus in Côte d’Ivoire. The most diversified families were Caesalpiniaceae, Mimosaceae, Euphorbiaceae, Rubiaceae and Fabaceae. The work of Bakenga et al. [13] , in Bukavu and its surroundings in South-Kivu in the East of the Democratic Republic of Congo noted 147 beeplants where the most represented families were Asteraceae, Fabaceae, Solanaceae, Caesalpiniaceae, Lamiaceae and Malvaceae. In the West of Cameroon, 78 species were registered by Dongock Nguemo et al. [1] , the most represented families were Asteraceae, Solanaceae and Euphorbiaceae. Meanwhile, the 51 melliferous plants collected were higher than those noted in the Western Chad where 25 species foraged by bees were reported by Gadbin [23] . Contrarily, it is Caesalpiniaceae that was the most frequent. Nonetheless 64 species registered in the Sudano-guinean of Togo by Aloma [30] were comparable to our results in the Guéra region. Globally, according to Lobreau-Callen and Damblon [3] in the Tropical region, as flowering plants were highly diversified and abundant, bees are very selective and forage the most attractive species near hives as such as spend less energy in their activity. They prefer very ornate foliage near the hives where they search the greatest suppliers of nectar among preferably species.

Honey of Guera region is divided in four biological types: trees, shrubs, small trees and herbaceous plants (Table 1). Trees are the most dominant (54.90%) and the least abundant was represented by small trees (3.92%). The analysis of variance indicates that there exists a significance difference between biological types (P < 0.05).

In the western highlands of Cameroon [1] , also in Bukavu and its surrounding South Kivu in the Eastern Democratic Republic of Congo [13] , in Burkina Faso [28] , it is rather herbaceous that were dominants. However, in the Sudano-Guinean zone of West Cameroon [4] and the Sudanian savanna area of North Eastern of Nigeria [5] , trees are predominant. Lobreau-Callen and Damblon [3] report that in the woody savannas at gallery forests proximity in Côte d'Ivoire and Nigeria, bees forage mostly on trees. On the other hand in the semi-arid area of Sudanian savannah, bees appear less selective because they forage at all plant strata. In the woody savanna of Cote d'Ivoire nearby galleries forest, in Nigeria and the Sudanian woody savanna, bees forage practically only trees. Lobreau-Callen and Damblon [3] specify that in the rainy season, bees are very selective and in priority exploit the flowering trees and shrubs, while in areas where grassland occupies a vast surface, herbaceous are more numerous. The biological type foraged by Apis mellifera adansonii varies with climate, season, morphological diversity and foraging behaviour.

Flower color is important feature for bees and other insects. Bees are highly visual insects. Eight colors of flower were observed. The diversity of flower can be explain by the experienced of bees in that region. Gumbert [31] indicate that inexperienced bees are known to have strong colour preferences. The white color is statistically (P < 0.05) the most frequent (23.52%) in the bee flora of the region; the greenish color is the least represented (3.92%). These results are in accordance with those obtained in the highlands of western Cameroon and in the Sudano-Guinean zone of West for the dominant melliferous plants, where the white flowers color were more dominant [1] [4] . It does not confirm the observations of Mbofung et al. [32] on plants visited by insects at Campo in the South Cameroon where it is the yellow color that is the most visited. Bakenga et al. [13] show that melliferous plants of Bukavu in the Democratic Republic of Congo present blue, beige, red, purple and pink as common color flower. Fægri and Van der Pijl [33] in such observations, describing the floral colours of melittophilous flowers as being mostly blue or yellow and this led to the concept of a flower syndrome for bee pollination. Observations made in the field among flower varieties differing in nectar content, bees chose among them according to the proportion of reward rather than by their colour [34] .

Bees need diverse pollen and nectar sources for balanced diet. Polliniferous plants (60.0%) were statistically (P < 0.05) highly represented compared to nectariferous plants (40.0%). Only five of these plants (Lannea humilis, Delonix regia, Cucumis sativus, Arachis hypogea and Mimosa invisa) provide both pollen and nectar to bees. These results were in accordance with those of Dongock et al. [1] in the Sudano-Guinean zone of West Cameroon. Contrary to our work, Bakenga et al. [13] noted that the plants visited by bees for nectar were well represented and constitute more than two thirds (45.6%) of the beeplants studied in Bukavu. Nectariferous plants exclusively (25.0%) have a higher proportion than in our results. Similarly plants visited for both pollen and nectar are less frequent (4.1%) at Bukavu [13] . However, in relation to our study zone, this represents almost a third of melliferous plants identified.

Concerning the domestication status of bee plants in Chad, both spontaneous and cultivated plants were identified. The spontaneous species were statistical (P < 0.05) the most frequent (81.0%) compared to the cultivated species (19.0%). These results are in agreement with those of Dongock et al. [1] [4] in the highlands of western Cameroon and in the Sudano-Guinean zone respectively where more than two thirds of beeplants identified were cultivated. These results are also similar to those of Lobreau-Callen and Damblon [3] in the vegetation of tropical West Africa and of Ricciardelli D’Albore [35] in the Mediterranean zone. The predominance of spontaneous plants indicates that the Chadian environment is less anthropised whereas the population density and endogenous knowledge plays an important role in the management of beeplants. According to Lobreau-Callen and Damblon [3] , the various races of Apis mellifera living in disturbed habitats, cleared, cultivated, highly anthropised area were perfectly capable for adapting to the deforested areas and crops replacing forest. In the North African regions, plantations of Eucalyptus, Citrus, Malus and Prunus orchards substituted the spontaneous flora. However, Lobreau-Callen and Damblon [3] conclude that in mosaic regions where patches of forest were kept close to the fields, the bees exploit preferably spontaneous flora. It seems that the behavior of bees is correlated to the structure of vegetation.