University of Vermont

Gund Director, Taylor Ricketts, Co-Authors a Science Article on the Importance of Wild Pollinators

Wild pollinators increase crop fruit set regardless of honey bees

Augochlorine bee visiting a tomato, USA

Taylor Ricketts, Director of the Gund Institute for Ecological Economics, is a co-author of a recent study published in Science that highlights the importance of the interaction between wild pollinators and production of animal-pollinated crops. An international research team of 50 authors led by Lucas A. Garibaldi (Universidad Nacional de Río Negro - CONICET, Argentina) analyzed the consequences of the abundance of wild pollinators for crop pollination. Pollination is a fundamental step in plant reproduction, and can therefore influence harvest of crops such as fruits, seeds, nuts, or stimulants like coffee. The study includes field data from 20 countries and 41 crop systems. The research team found that the benefits of pollination by wild insects to the number of fruits or seeds produced per flower cannot be replaced by managed honey bees. Both wild insects and honey bees are needed to maximize fruit set. Therefore, the ongoing loss of wild insects in many agricultural landscapes likely has negative consequences for crop harvest. These findings prompted an urgent call to maintain and manage pollinator diversity in agricultural landscapes for long-term agricultural production.

Human survival depends on many natural processes, which do not have a direct market value, such as nutrient cycling, climate regulation, water purification, pest regulation and plant pollination. Paradoxically, changes humans have made to landscapes, such as conversion of natural habitat to human uses and agricultural intensification, can compromise these ecosystem services. Pollination of crops by wild insects is one such vulnerable ecosystem service, as wild insects are declining in many agricultural landscapes. Flowers of most crops need to receive pollen before making seeds or fruits, and pollen transfer can be enhanced by insects that visit flowers. These insects usually live in natural or semi-natural habitats, such as forest margins, hedgerows or grasslands. As these habitats are lost from cropping landscapes, pollinator abundance and diversity decline and crops receive fewer flower visits. The most important crop pollinators includes bees, beetles, flies, butterflies, birds and bats.

This paper 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 results of this study reveal that new practices for integrated management of both honey bees as an agricultural input and diverse assemblages of wild insects as an ecosystem service will enhance global yields of animal-pollinated crops and ensure long-term agricultural production. These practices should include conservation or restoration of natural or semi-natural areas within croplands, promotion of a variety of land use, addition of diverse floral and nesting resources, and more prudent use of insecticides that can kill pollinators.

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