Impacts of honeybee density on crop yield: A meta-analysis

ROLLIN, ORIANNE; GARIBALDI, LUCAS A.

JOURNAL OF APPLIED ECOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2019 vol. 56 p. 1152 - 1163

0021-8901

1. There isincreasing recognition that pollination deficits are limiting cropyields world-wide. However, management strategies for optimal insectpollination are still unclear for most crops. Current managementfocuses on providing high densities of honeybees, but recommendeddensities are highly variable, even within single crops andcultivars.2. We performed anextensive literature search to record honeybee densities (colonydensity and/or flower visitation rates) and crop productivity (fruitset, seed set, fruit weight and/or yield). Effect sizes wererepresented as the difference in crop productivity between the twomost extreme levels of honeybee densities.3. Out of 795reviewed studies, only 22 analysed the effect of at least two levelsof honeybee densities on crop productivity (reporting 60 resultingeffect sizes in total). Moreover, few recommendations for croppollination management are based on results from controlledexperimental designs, and with comparable methodology.4. We found thatboth colony density and visitation rates increased all theproductivity variables. However, effects were nonlinear forvisitation rates, suggesting that there is an optimum (mean of 8?10visits per flower) beyond which more honeybees are not beneficial(and can even be detrimental) for crop productivity.5. Effect sizes forvisitation rates were greater than that for colony densities,suggesting that visitation rates are a more direct measure of thepollination process. Data on the relation between colony density andvisitation rates are lacking. Interestingly, effect sizes forvisitation rates were greater for crops with separate sexes thanthose with hermaphroditic flowers; therefore, the benefits ofhoneybee pollination vary according to the crop biology.6. Synthesis andapplications. Current practices for crop pollination assume that morehoneybees are always better for crop yield, even if the effect ofthis management on crop production still unclear. In contrast, ouranalyses suggest that there is an optimum for honeybee densities.Despite the importance of honeybees and pollinator-dependent cropsworld-wide, there is a lack of studies designed for finding such anoptimal level of crop pollination. Our analyses further suggest thatvisitation rates could be used as a proxy to guide managementrecommendations such as colony density and spatial arrangement.p { margin-bottom: 0.25cm; line-height: 120%; }