Quantifying the pollination ecosystem service provided by non-Apis bees in tomato production

Abstract

Pollination provided by bee species is a key contributor to the reproductive success of a wide variety of crops. In South Africa, tomato (Solanum lycopersicum) is among the most important cash crops. Tomato flowers are self-fertile and self-pollinating. The anthers of tomato flowers are poricidal and connivent, though tightly held together in a cone by interlocking hairs along their edges, bees that can perform vibratile pollination can access pollen grains from these flowers. During buzz pollination, some species of bees cling on the anthers of tomato flowers by means of their mandibles which then results in vibration of the flowers. This biting action cause “bee kisses” (brown marks) on the flowers and these marks can be used to confirm that the flowers have been visited by bees and that pollination might have taken place. There is little information available on the pollination status of tomatoes in South Africa, therefore, the aim of this study was to quantify the pollination ecosystem service provided by bee species to tomato production in the Limpopo Province, South Africa. The objectives of the study were to: 1) determine the effect of field proximity to natural vegetation on bee visitation rates on tomato flowers in four bio-climatic areas, 2) describe bee species that provide pollination ecosystem service to tomato flowers, and 3) determine the effect of pollination provided by bees on the yield and quality of tomatoes. This study was conducted on four farms (Waterpoort, Vreedzaam, Jachtpad and Dikgale) from April to December in 2018 and 2019. Data were collected inside tomato fields along four transects which were separated using four distance intervals. Results showed that bee visitation rates varied between farms. This could be attributed to different planting months/seasons between the various study areas which was directly linked to different temperature regimes as well as different vegetation types. In addition, the distance from the natural vegetation also influenced bee visitation rates. The latter was higher, closer to natural vegetation (< 50 m) and differed significantly from visitation rates recorded at the furthest distance in two of the farms (> 200 m). The potential pollinators collected during the study were largely from the Apidae family, and three genera i.e. Xylocopa, Apis and Amegilla. The Megachilidae with one genus, i.e. Megachile, was the second most abundant family. Furthermore, an exclusion experiment was conducted to compare the effect of bee pollination and self-pollination on yield and quality of tomatoes. Bee pollination had a positive impact on the quality of tomato fruit particularly in terms of fruit weight, height and diameter. The fruits harvested from bee-pollinated flowers had a significantly larger size when compared to fruits obtained from the enclosed flowers while there were also fewer malformed fruits. This study highlighted the importance of bee species in tomato production. It is therefore important to develop management practices that will aid in improving bee visitation rates, abundance and diversity in order to improve tomato production.