Body size as a proxy of probing time and visitation rates on cucumber by two African stingless bees increase fruit quality and seed quantity

Pollinators are of essential importance for sustainable agriculture. However, pollination efficiency depends on interacting factors such as pollinator behaviour and morphology. We compared the effect of probing time length and visit frequency of two distinct body size African stingless bee species (Meliponula bocandei, Dactylurina schmidti) as alternative pollinators to Apis mellifera scutellata on greenhouse cultivated cucumber. We found differences in morphometric characteristics, between a set of 9 body parameters. Bee body size was the morphological feature that varied the most among bee species. On average, body size was largest in honeybees, followed by M. bocandei, and finally D. schmidti, which was the smallest. Glossa length was different between the bee species: A. mellifera scutellata (2.86 ± 0.026 mm), M. bocandei (2.20 ± 0.031 mm), D. schmidti (0.72 ± 0.025 mm). Such differences among bee species in body parameters correspondingly affected nectar probing times during a single flower visit, which were different for the bee species. D. schmidti (3.34 ± 0.56 s) had the longest probing time, while M. bocandei (2.57 s) had the shortest. Fruit quality was strongly positively influenced by the visit duration during a single visit on female flowers. The slope of fruit quality produced was higher in flowers pollinated by M. bocandei. During a single flower visit, heavier and bigger fruits were obtained in the gold standard hand cross pollination and flowers pollinated by M. bocandei. The bee species and the number of visits significantly impacted fruit weight, fruit volume and number of seeds. Subsequent visit performed by M. bocandei positively impacted fruit quality. Three visits on a flower were enough to ensure the production of high-quality fruits. Fruit sweetness depended on the number of visits received by the flower, but not on the bee species that performed the visit. Altogether, our results indicate that the stingless bees M. bocandei is more an efficient pollinator of cucumber than A. m. scutellata and D. schmidti and can be recommended for use under greenhouse cultivation.