Changes made by humans to the natural landscapes can often compromise ecosystems, which paradoxically are vital for human survival. Pollination of crops by wild insects is one such vulnerable ecosystem service, as wild insects are declining in many agricultural landscapes. The study, recently published in Science, focused on understanding whether the ongoing loss of wild insects impacts crop harvest. For this purpose, the researchers compared fields with abundant and diverse wild insects to those with degraded assemblages of wild insects across 600 fields at 41 crop systems on all continents with farmland.
The study found that fruit set, the proportion of flowers setting seeds or fruits, was considerably lower in sites with less wild insects visiting the crop flowers. Therefore, losses of wild insects from agricultural landscapes will likely impact both our natural heritage and agricultural harvest.
As hives of the honey bee are frequently added for improved pollination, the researchers asked whether this application can compensate for limited abundance and diversity of wild insects and fully maximize crop harvest. They found that variation in honey bee abundance improved fruit set in only 14% of the crop systems they served. Furthermore, wild insects pollinated crops more effectively because an increase in their visitation enhanced fruit set by twice as much as an equivalent increase in honey bee visitation. Importantly, high abundance of managed honey bees supplemented, rather than substituted for, pollination by wild insects.
These results hold even for crops stocked routinely with high densities of honey bees for pollination, such as almond, blueberry, mango or watermelon. Although honey bees are generally viewed as a substitute for wild pollinators, this study demonstrates that they neither maximize pollination, nor fully replace the contributions of diverse, wild-insect assemblages to fruit set for a broad range of crops and agricultural practices on all continents with farmland.
The leading author, Lucas A. Garibaldi, Universidad Nacional de Río Negro - CONICET, Argentina comments: "Our study shows that losses of wild insects from agricultural landscapes impact not only our natural heritage but also our agricultural harvests. We found that wild insects consistently enhanced the number of flowers setting fruits or seeds for a broad range of crops and agricultural practices on all continents with farmland. Long term, productive agricultural systems should include habitat for both honey bees and diverse wild insects. Our study prompts for the implementation of more sustainable agricultural practices."
Alexandra-Maria Klein, Leuphana University of Lüneburg, Germany adds: "Ecosystem services can depend on biodiversity provided by wild organisms. Intensified agriculture separates crop production and biodiversity. Our study shows that this separation can have negative consequences for pollination services not buffered by honeybee management. We urgently need more research that informs but also involves the global and wider society to explore novel management designs for agricultural landscapes."
Lucas A. Garibaldi
Universidad Nacional de Río Negro, Argentina
Leuphana University of Lüneburg, Germany
Julius Maximilian University of Würzburg
Department of animal Ecology and Tropical Biology, Germany
Garibaldi L.A., Steffan-Dewenter I, Winfree R, Aizen M.A., Bommarco R., Cunningham S.A., Kremen C., Carvalheiro L.G., Harder L.D., Afik O., Bartomeus I., Benjamin F., Boreux V., Cariveau D., Chacoff N.P., Dudenhöffer J.H., Freitas B.M., Ghazoul J., Greenleaf S.,Hipólito J., Holzschuh A., Howlett B., Isaacs R., Javorek S.K., Kennedy C.M., Krewenka K., Krishnan S., Mandelik Y., Mayfield M.M., Motzke I., Munyuli T., Nault B.A., Otieno M., Petersen J., Pisanty G., Potts S.G., Rader R., Ricketts T.H., Rundlöf M., Seymour C.L., Schüepp C., Szentgyörgyi H., Taki H., Tscharntke T., Vergara C.H., Viana B.F., Wanger T.C., Westphal C., Williams N., Klein A.M. Wild pollinators enhance fruit set of crops regardless of honey-bee abundance. Science