An interstate team of researchers compared different land cover types commonly occurring in agricultural regions as predictors of wild bee visitation to flowers in apple orchards. They found that the amount of open grassy areas in the landscape was the best predictor of wild bee visitation, probably because the dominant orchard-visiting wild bees were soil-nesting that are relatively tolerant of agricultural environments. Further, wild bee visitation to apples was very low or even zero in some regions and years, and the vast majority of flower visits were made by honeybees suggesting that managing wild bees by altering land cover will have little impact on pollination services to apples in southeast Australia.
Julian Brown, Scott V.C. Groom, Romina Rader, Katja Hogendoorn, Saul A. Cunningham. Land cover associations of wild bees visiting flowers in apple orchards across three geographic regions of southeast Australia. Agriculture, Eco-systems & Environment, Volume 324, 2022, 107717, https://doi.org/10.1016/j.agee.2021.107717.
Efficiency and effectiveness of native bees and honey bees as pollinators of apples
Pollination biologists from Western Sydney University studied apple crops in New South Wales orchards to evaluate the insect abundance and efficiency. They found that rare, native Exoneura (reed bees) and halictid bees were the most efficient apple pollinators. Stingless bees had low pollination efficiency, but high abundance and effectiveness. Bees that contact the stigmas deposit more pollen per visit than non-bees. Native stingless bee, Tetragonula carbonaria, foragers carried the most loose apple pollen on their bodies, followed by honey bees, but most individual insects (52%) visiting flowers carried no apple pollen at all. Bees carried more apple pollen on their bodies than all non-bee insects. In addition, when contacting flower stigmas, bees deposited more pollen per visit than non-bees.
Pink Lady apples require pollination, because closed controls set zero fruits. Fruit set also required repeated pollinator visits, because flowers restricted to a single insect visit rarely set fruit. Pollination deficits were detected in both study regions, wherein open treatments set fewer fruits than hand-pollination treatments. Pollination ser-vices were predominantly provided by honey bees (97%) in one region (Orange), but in a second region (Bilpin), honey bees (60%) were complemented strongly by wild stingless bees (35%). Hence, in Bilpin, native bee pollination services may buffer predicted decreases in honey bee populations, should the Varroa mite become established in Australian agro-environments.
Olivia M. Bernauer, Simon M. Tierney, James M. Cook. Efficiency and effectiveness of native bees and honey bees as pollinators of apples in New South Wales orchards. Agriculture, Ecosystems & Environment, Volume 337, 2022, 108063, https://doi.org/10.1016/j.agee.2022.108063.
A wild bee visiting an apple flower, Photo by Ryan Graybill.
Plant-bee interaction networks for each region. Lines connecting plants (boxes on right side of each network) to bees (boxes on left side of each network) indicate presence of interaction, and line width increases with observed visitation rate relative to other pair-wise interactions. Box height is proportional to number of visits received (plants) or made (bees) within each region. Plants are grouped into weeds (black boxes), native plants (dark gray boxes), and apples (white boxes).