Pollination services by wild pollinators
|Crop pollination relies mainly on managed hives of the domesticated honey bee|
|Yael Mandelik, firstname.lastname@example.org|
|November 3, 2019|
Biodiversity and Ecosystem Services Lab, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem.
Pollination by animals is crucial for the sustainability of both natural and agricultural ecosystems. An estimated 88% of all angiosperm plant species are animal-pollinated, and 77% of the leading global food crops, including the majority of edible fruits, nuts and seeds, depend on animal pollinators for yield quantity and quality. Crop pollination relies mainly on managed hives of the domesticated honey bee (Apis mellifera). However, this species is increasingly difficult to manage due to combined effects of parasites, diseases and pesticide exposure. In addition, honey bees do not pollinate all crops efficiently, and supplementary pollination may be needed. Wild bees, naturally occurring populations of globally over 20,000 species, may contribute substantially to pollination of a variety of crops, and provide a safety net in the event of honey bee collapses.
Fig 1 (a) Gideon Pisanty, a former PhD student in the lab, conducting field experiments of single visit pollination efficiency in a watermelon field in the Judean Foothills. Gideon is patiently waiting for a wild bee to visit a marked flower he observes. After the bee leaves the flower it will be bagged and monitored for fruit and seed set.
Israel, with over 1100 recorded bee species, is a hot spot of bee diversity. Studies in different parts of country revealed rich and abundant bee communities inhabiting various agricultural landscapes. In order to assess the contribution of these wild bees to crop pollination, pollination experiments were conducted in different crops, including watermelon, sunflower, strawberry, almond, and apple.
Experiments include measuring the pollination efficiency of single bee visits, conducted for each of the dominant bee species found in the fields. This is done by exposing a fresh virgin flower to a single bee visit and consequently monitoring fruit and seed set (Fig 1). This measurement is repeated several times for each of the dominant bee species, until a reliable estimation of single bee visit pollination efficiency is achieved. This measure is then multiplied by the visitation rate (number of bee visits/flower/time) of each species to arrive to species-specific estimation of contribution to crop pollination. Using this methodology, we found that commercial honey bees and wild bees complement each other in their pollination activity; wild bees are most efficient in pollinating small flowers, while honey bees show the opposite pattern (Fig 2a). Similarly, wild bees are more abundant in fields surrounded by increased amount of semi-natural habitats, while honey bees don’t show this pattern (Fig 2b, c). As a result, fields in which both honey bees and wild bees are active and pollinating flowers, receive overall higher pollination services and produce higher yields compared to fields where only honey bees are present.
Fig 1 (b) A common crop pollinator wild bee, Lasioglossum malachurum, pollinating a watermelon flower. The body of the bee comes in contact with the yellow pollen and transfers it to the flower female organs (stigma).
After: Pisanty G, Afik O, Wajnberg E, Mandelik Y (2016). Journal of Applied Ecology 53: 360-370
Fig 2 (a) The effect of flower size (measured as ovary width) on single visit pollination efficiency (measured by % of fruit set) of honey bees (HB) and wild bees (WB). Numbers represent the number of replicates.
Fig 2 (b) The effect of surrounding land use (presented as % of semi-natural habitats in 50 m radii buffers around study fields) on honey bees (HB) and wild bees (WB) abundance within fields (presented as # of bee visits per 20 min of observations).
After revealing the significant contribution that wild bees can provide to crop pollination in Israel, we aimed to create an ecological profile for main wild crop pollinators to improve our ability to manage and conserve them. We studied their life-history traits and habitat requirements and found that main crop pollinators were generalist foragers, ground nesters, of small and medium body size (compared to honey bees). In a national scale study, we aimed to evaluate the contribution of different land-use types to the richness and abundance of wild bee communities, and to the delivery of pollination services to agriculture. We focused on the seasonal availability of two resources known to shape pollinator communities, foraging and nesting resources. For each main land-use type we estimated the relative amount of foraging (flowers) and nesting resources (different substrates above and below ground) it potentially provide along bee activity season (February till October).
Finally, for each land-use category, we averaged its foraging and its nesting scores to obtain a final score for land-use suitability for wild bees. In the Agricultural land-uses we deducted a relative “pesticide penalty” from the scoring obtained; the penalty ranged from 0-1, and was determined based on expert opinion. We found that different land-use categories may vary considerably in their expected contribution to the richness and abundance of wild bee communities (Fig 3).
Fig 3. Relative contribution of Israel’s open landscapes to wild bee communities as a proxy for the delivery of wild bee pollination services.
After: Lotan A, Kost R, Mandelik Y, Peled Y,
Two main patterns immerged from our scoring process. First, agricultural land-uses are ranked lower compared to natural and semi-natural land-use types. This is due to the “pesticide penalty” applied to the agricultural land-uses and their relative short bloom period compared to natural/semi-natural land-uses. Second, regenerating semi-natural habitats, may have higher value for wild bees compared to natural perennial-dominated land-uses. Accordingly, mapping the contribution of different land-uses to wild bee richness and abundance, and to the expected delivery of pollination services, shows highest values in regions characterized by dwarf shrubland dominated by annuals, as in the Golan Heights (Fig 3). Areas with high amount of natural/semi-natural habitats, such as the Judean foothills and upper Galilee, have also high values, while areas that are developed and/or used for agriculture, such as most of the coastal plains and the northern valleys, have lowest contribution to wild bee communities and pollination services.
Chakuki D, Zemah Shamir S, Ram Y (2018). One Ecosystem 3: e25494 https://doi.org/10.3897/oneeco.3.e25494