Protected agriculture is highly dependent on insect pollination, and this process is essential for success in Mexico, greenhouse crops have rapidly increased (^{INEGI, 2007}) practice. The tomato (Solanum lycopersicum Miller) is one of the main vegetables planted in our country, ranking in 2011, as the tenth largest producer of tomato worldwide, with a total of 2 435 790 tonnes (^{FAO, 2011}). The tomato plant has poricida dehiscence, the anthers need to be shaken to release their pollen through some apical pores (^{Buchmann, 1983}).

In the open field is provided by the wind, which in most cases is sufficient to trigger the release of pollen, promoting self -fecundation (^{Free, 1993}), while in greenhouse there are few air-flows, so it is advisable to use of pollinators, since the vast majority of flowering plants (angiosperms) depend primarily through the pollination of insects. In the open field, the best known insect for this purpose is the European honeybee Apis mellifera L.; however, A. mellifera, is not the best species for pollination in some crops, because of the particular morphology of the flower (^{Cunningham et al., 2002}).

The bumblebees of the genus Bombus the most used in protected agriculture, it is estimated that each year worldwide more than one million hives of bees for pollination in greenhouses are consumed (^{Velthuis, 2006}). Good results have been reported for other species of Apidae in the pollination of greenhouse crops, as in the case of Scaptotrigona depilis and Nannotrigona testaceiconis for strawberry (^{Roselino et al., 2009}) and Melipona subnitida for growing peppers (^{Oliveira et al., 2005}), Nannotrigona perilampoides in habanero pepper (^{Palma et al., 2008}) and Bombus ephippiatus in tomato (^{Torres, 2012}).

However, the most used species in Mexico for pollinating is Bombus impatiens, native of eastern Canada and the United States (^{Velthuis, 2006}) exotic species, so that the risk of health damage to native species and invasion runs ecosystem as has happened in other parts of the world, as in the case of Bombus terrestris originally from Europe, invading Argentina (^{Turret, 2006}), Tasmania (^{Semmens and Turner, 1993}) and possibly our country (^{Winter et al., 2006}). The idea of reducing these risks is to implement the use of native species such as Bombus ephippiatus, bumblebee with distribution in Mexico, inhabiting mountain regions (^{Fuentes and Madrid, 2003}) and the stingless-bee Scaptotrigona mexicana and Partamona bilineata widespread in our country in the Gulf of Mexico and Yucatan Peninsula (^{Ayala, 1999}). So in this paper the effects of four species of Apidae about the quality of tomatoes grown in greenhouses in order to determine the potential of Mexican species for use as pollinators in the southeastern region of Coahuila was evaluated.

This study was conducted in four greenhouses of 1 000 m² in Arteaga, State of Coahuila de Zaragoza. The greenhouses were rectangular with multi-span gabled and passive ventilation; covered with plastic brand klerk 50, the thickness of 15mm/6 mil/600 gauges in its second year four guaranteed by the manufacturer; total light transmission of 65% to 45%, shadow 35% to 55%, diffuse light transmission 33%, ambient temperature of min / max -50/85 °C, friendly with the bumblebees (^{AGROEXPO, 2013}). Temperatures presented during the experiment ranged from 6-42 °C, relative humidity 60-80%. The hybrid tomato cultivar used was ball type "Charlotte" with a planting density of five plants per m², keeping in line with standard business practices without making fruit thinning.

Four hives from different companies were acquired, Bombus impatiens (Koppert of Mexico) and Bombus ephippiatus (Bioinsectum), in the case of bees without sting Scaptotrigona mexicana and Partamona bilineata were acquired in the Municipality of Xicotepec Juarez, Puebla State, in an apiary/meliponary named “Comercializadora Monte” moving them from wild nests in wooden boxes with a “piquera” on top of the front of the box; all the hives were placed in the centre of one of the nave, at 60 cm from the ground and protected from the light, while the control was a greenhouse of 250 m², each hive with its own greenhouse was considered as a treatment, while the control was a greenhouse without pollination.

At harvest time, each greenhouse was divided into four zones, taking representative samples of each, each treatment consisted of four replicates, each replicate with 24 sampling units (tomato), such repeats were harvested each week throughout the month of May, 2012. Data collection was performed by marking open flowers 3 days after installed beehives sufficient time for acclimatization in greenhouse conditions agronomic parameters were evaluated as: fruit weight (g), polar diameter (cm), equatorial diameter (cm) and fruit weight (g).

Within the assessments of the polar diameter (Table 1), we can see that for the case of two species of stingless bees, it had no effect on this parameter, behaving quite similarly to the control without pollinators. Regarding Partamona bilineata one of the factors that might have affected its role as a pollinator is its heavy reliance on the nest (^{Camargo and Silvia, 2003}), since the process of accommodating new nests, involves choosing and transporting materials for processing (^{González et al., 2011}), leaving little time for foraging.

Table 1 Comparison of means of four pollinator species on polar and equatorial diameter in tomato variety Charlotte. 

N= número de medidas; *= centímetros; SD= desviación estándar= Ag= agrupación mediante tukey.

In the case of Scaptotrigona mexicana, foraging was observed only during daylight hours, which exceeded 25 °C; so for this species have been reported works with good effectiveness in subtropical climates (^{Nates, 2005}), otherwise the area where our experiment was developed (mountain).

While for this bumblebees, statistical difference was found in relation to other treatments. Studies in bumblebees of the genus Bombus, refer that they have traits that make them excellent pollinators of many crops, including tomato (^{Buchmann, 1992}) for our study, Bombus impatiens was the insect with the greatest effect on the polar diameter as a pollinator to 6.9213 cm followed by Bombus ephippiatus with 6.6434 cm on average (Table 1). In this regard we mention that B. impatiens is an introduced species, due to its high effectiveness allowing marketing.

However, given the importance attached to the use of bees as pollinators, techniques of domestication on the use of native bumblebees have developed (^{Estay, 2009}) as in the case of B. ephippiatus, a colony experimentally bred from wild queens, for this reason we propose to continue with investigations of this native species and widely distributed in Mexico and Central America, which will develop a product that caters the need of domestic producers of tomato. In relation to the equatorial diameter, stingless bees were those that showed a higher measure on the effect of pollination (Table 1); however, ^{De la Cruz et al. (2009)} mentioned that, the polar diameter parameter influences more about the mass of fruit equatorial diameter. Also, ^{Aldazábal et al. (2002)} mentioned that, the relationship between the volume and weight equatorial measures, ball-type tomatoes, is more influenced by the polar diameter.

For the size of the fruit, the best results were for bumblebee species with values of 207 978 g for Bombus impatiens and 199 746 for B. Ephippiatus (Table 2). González (2007) mentioned that, the bumblebees are the best alternative for larger fruits. Likewise, we can mention that, the bees of the genus Bombus are effective pollinators due to their larger size and dense hairs covering its body, causing from turning the anthers and vibrating their flight muscles without flying (pollination zoom) allowing to transfer more pollen grains per visit (^{Willmer et al., 1994}), making bumblebees excellent pollinators of cultivated plants. ^{Vergara et al. (2006)} mentioned that B. ephippiattus shows similar results in size, shape, sugar content and time to maturity to those produced with the traditional method of pollination by mechanical vibration.

Table 2 Comparison of means of four pollinator species on the weight of tomato fruits. 

N= número de medidas; *= gramos; SD= desviación estándar; Ag= agrupación mediante tukey.

Therefore we mention that, the use of bumblebees such as B. ephippiatus and B. terrestres improve fertilization, increasing the polar diameter, size and mass; while native stingless-bees, being tropical climates in our experiment forage and pecoreadora activity was limited to a few hours, when temperatures exceeded 25 °C. As the bees are a good option compared to Apis meliera having nomalinismo behavior may leave the nest and getting together with the crop pollination problems (^{Palma et al., 2008}).