# Bumblebee Pollination Enhances Yield and Flavor of Tomato in Gobi Desert Greenhouses
## 1 Introduction  
Tomato, _Lyopersicum esculentum_, is one of the most popular vegetables worldwide. China is the world's largest producer of tomatoes, both by area (hectares) and volume (tonnes) [1]. Protected cultivation, which can help growers overcome climate limitations and maximize profitable harvest, has been the most important cultivation systems in China [2]. In recent years, these protected cultivations, and tomatoes in particular, have expanded rapidly in Northwest China. However, pollination remains a limiting factor in greenhouse tomato cultivation. Tomato flowers depend on pollination to produce seeds and fruits [3]. Studies have shown that tomato fruit-setting is highly correlated with pollen deposition on stigma, and limited pollination usually resulted poor fruit set [4]. Tomato is a buzz-pollinated crop, its flowers are self-compatible but the pollen is kept locked in non-dehiscent anthers, meaning that vibration is necessary to release high volumes of pollen for self-fertilization [5]. Underprotected cultivation conditions, where wind and wild insects are absent, commercially acceptable fruit set and quality are difficult to achieve without artificial pollination methods. Electric or manual vibrators were found to be an effective artificial pollination method in tomato greenhouses [4]. Compared to tomatoes without vibration treatment, vibrator-treated tomatoes ripened earlier and had greater yield. Plant growth regulator (PGR), which chemically induce fruit growth, are another widely used method in greenhouse tomato production [6; 7]. However, both vibrator and PGR treatments have high labor costs and produce tomatoes with an unstable yield and quality. The development of biological control and reduced use of chemical pesticides on crops made it possible to use bee pollinators in tomato greenhouses. Bee pollination is an efficient production technique in agriculture [8; 9; 10; 11] and makes a huge economic contribution globally [12; 13; 14; 15]. As the most widely used managed pollinator, several studies have explored the use of western honeybee, _Apis mellifera_ L., in greenhouse tomato pollination, demonstrating improved yield and quality compared with greenhouses without honeybees [16; 17; 18]. However, studies have also showed that honeybee pollination efficiency in tomato greenhouses was variable and honeybee pollinated-tomato often couldn't meet the commercial production level [19; 20; 21]. In our previous study, we found that the innate dislike of tomato floral scent and unsuccessful food-collecting experience might explain the low foraging activity of honeybee in tomato greenhouse [22]. More studies are needed to understand and enhance honeybee foraging activity before honeybee colonies can be used for the pollination of greenhouse tomato. Bumblebees are effective bee pollinators of tomato as, unlike honeybees, they are capable of buzz pollination to vibrate tomato anthers to release pollen grains and only one visit is sufficient for full tomato pollination [23]. Following the success of commercially rearing bumblebee colonies bumblebee pollination has become a standard practice in developed agricultural countries and regions [24]. Besides saving labor, many studies showed that bumblebee pollination can significantly improve tomato yield and quality [25; 26; 27; 20]. Beyond yield and quality, fruit flavor is an increasingly important concern for growers, as more and more consumers have complained about the poor flavor of commercial tomato in recent years [28]. Tomato fruit flavor is determined by a complex of sugars, acids, and volatiles [29]. Many factors, such as variety and postharvest storage environment, can affect the flavor of tomato fruits [29; 30; 31; 32; 33; 34]. Previous studies have demonstrated that bumblebee pollinated-tomatoes had a better flavor than PGR or vibrator-treated tomatoes [35] and consumers had higher willingness to pay for bumblebee pollinated tomatoes than PGR-treated tomato, despite the higher prices for bumblebee pollinated tomatoes [36].